Two instruments based on differential optical absorption spectroscopy (DOAS) were developed to accurately measure ammonia concentrations in the atmosphere without inlet or interference issues. The RIVM DOAS instrument can measure concentrations up to at least 200 μg m-3 with high accuracy of 0.15 μg m-3 for 5-minute averages over a 100 m path. A smaller miniDOAS was also developed for network monitoring, having similar accuracy but reduced size, costs, and complexity. Both instruments were tested alongside a conventional instrument during a field campaign, showing excellent agreement and faster response without memory effects. The DOAS instruments are well-suited for flux measurements using a gradient setup due to their open-path design and high accuracy.
The objective is to analyze and propose a methodology to manage with the attenuating effect promoted by carbon dioxide - CO2 on the performance of ultrasonic flow meter in gas flaring applications. Such methodology is based on experiments performed in a wind tunnel with a Reynolds number about 10^4 and concentration of CO2 above 60%. The results indicate that the ultrasonic meter exhibited measurement readings failures, especially in stages of abrupt changes in gas concentration, whose contents were above 5%. It is verified, as well, that the approximation of ultrasonic transducers tends to reduce such measurement failures.
Implication of Applying CALPUFF to Demonstrate Compliance with the Regional ...BREEZE Software
In this paper, a case study of applying the CALPUFF modeling for regional haze analysis is conducted for an industrial source with potential impact on a nearby Class I area. Results for a base case are discussed and influences of several variables on modeling results are evaluated.
In this paper, the results of CAMx modeling analyses as well as monitoring data to explore the general characteristics and patterns for the 8-hour averaging ozone concentrations, as compared to those of the 1-hour averaging ozone concentrations, in an example ozone non-attainment area will be discussed.
High-accuracy laser spectrometers for wireless trace-gas sensor networksClinton Smith
The document outlines Clinton J. Smith's final public oral exam for his dissertation on developing laser spectrometers for wireless trace gas sensor networks. The dissertation aims to develop CO2 sensors for deployment in a real-time sensor network to monitor carbon fluxes over a broad area. The outline includes development of a wireless laser spectroscopic sensor node for atmospheric CO2 monitoring, quantifying and improving the accuracy of wireless sensor network nodes, developing a solar-powered distributed wireless CO2 monitoring network, techniques for real-time calibration, and conclusions. Laboratory and field tests show the sensors can accurately measure CO2 concentrations with precision below 1% and linear response over large concentration ranges.
This document summarizes a seminar presentation on detecting radon concentration using an air flow meter. It includes:
- An introduction to radon and its health effects
- The aim of determining radon progeny concentration in the atmosphere
- A description of how an air flow meter works to draw air through a filter paper at a known rate
- The procedure of collecting aerosols on the filter paper and measuring alpha particle emissions
- Calculations using the Tsivoglou method to determine radon progeny concentrations from counting rates
- Results showing progeny concentrations increased with humidity
Satellite-and Ground-based Red Tide Detection Method and System by Means of P...Waqas Tariq
A method for detection of red tide by means of remote sensing reflectance peak shift is proposed together with suspended solid influence eliminations. Although remote sensing reflectance peak is situated at around 550nm for sea water without suffered from red tide, the peak is shifted to the longer wavelength when sea water is suffered from red tide. Based on this fact, it is capable to detect red tide using high wavelength resolution of spectroradiometers. The proposed system uses green color filtered cameras. Acquired imagery data can be transmitted through wireless LAN to Internet terminal and can be archived in server through Internet. This is the proposed ground based red tide monitoring system. The paper also proposes a method for removing suspended solid influence on red tide suffered area estimations. The proposed method and system is validated in laboratory and field experiments. The system is deployed at coastal areas of Ariake Sea in Kyushu, Japan.
Early kick detection and nonlinear behavior of drilling mu…Frank-Michael Jäger
The following test measurements serve the quantification of resolution and achievable sensitivity of parameters of sound velocity and sound absorption in wellbore fluids. More precisely, these studies refer to tools and methods to identify the flow of liquids or gases, preferably hydrocarbons in the well bore in real time during the drilling. The aim is a way to show with the highly sensitive and robust tools for use in the deep ocean can be realized.
This document discusses air pollution engineering topics including air emissions modelling and sampling, and air pollution abatement equipment. It provides definitions of air pollution and classifications of air pollutants. It also describes common methods for air sampling and modelling to measure and estimate air pollution levels. Finally, it outlines environmental risk assessment procedures and discusses common equipment used to control and remove airborne particulates like electrostatic precipitators and fabric filters.
The objective is to analyze and propose a methodology to manage with the attenuating effect promoted by carbon dioxide - CO2 on the performance of ultrasonic flow meter in gas flaring applications. Such methodology is based on experiments performed in a wind tunnel with a Reynolds number about 10^4 and concentration of CO2 above 60%. The results indicate that the ultrasonic meter exhibited measurement readings failures, especially in stages of abrupt changes in gas concentration, whose contents were above 5%. It is verified, as well, that the approximation of ultrasonic transducers tends to reduce such measurement failures.
Implication of Applying CALPUFF to Demonstrate Compliance with the Regional ...BREEZE Software
In this paper, a case study of applying the CALPUFF modeling for regional haze analysis is conducted for an industrial source with potential impact on a nearby Class I area. Results for a base case are discussed and influences of several variables on modeling results are evaluated.
In this paper, the results of CAMx modeling analyses as well as monitoring data to explore the general characteristics and patterns for the 8-hour averaging ozone concentrations, as compared to those of the 1-hour averaging ozone concentrations, in an example ozone non-attainment area will be discussed.
High-accuracy laser spectrometers for wireless trace-gas sensor networksClinton Smith
The document outlines Clinton J. Smith's final public oral exam for his dissertation on developing laser spectrometers for wireless trace gas sensor networks. The dissertation aims to develop CO2 sensors for deployment in a real-time sensor network to monitor carbon fluxes over a broad area. The outline includes development of a wireless laser spectroscopic sensor node for atmospheric CO2 monitoring, quantifying and improving the accuracy of wireless sensor network nodes, developing a solar-powered distributed wireless CO2 monitoring network, techniques for real-time calibration, and conclusions. Laboratory and field tests show the sensors can accurately measure CO2 concentrations with precision below 1% and linear response over large concentration ranges.
This document summarizes a seminar presentation on detecting radon concentration using an air flow meter. It includes:
- An introduction to radon and its health effects
- The aim of determining radon progeny concentration in the atmosphere
- A description of how an air flow meter works to draw air through a filter paper at a known rate
- The procedure of collecting aerosols on the filter paper and measuring alpha particle emissions
- Calculations using the Tsivoglou method to determine radon progeny concentrations from counting rates
- Results showing progeny concentrations increased with humidity
Satellite-and Ground-based Red Tide Detection Method and System by Means of P...Waqas Tariq
A method for detection of red tide by means of remote sensing reflectance peak shift is proposed together with suspended solid influence eliminations. Although remote sensing reflectance peak is situated at around 550nm for sea water without suffered from red tide, the peak is shifted to the longer wavelength when sea water is suffered from red tide. Based on this fact, it is capable to detect red tide using high wavelength resolution of spectroradiometers. The proposed system uses green color filtered cameras. Acquired imagery data can be transmitted through wireless LAN to Internet terminal and can be archived in server through Internet. This is the proposed ground based red tide monitoring system. The paper also proposes a method for removing suspended solid influence on red tide suffered area estimations. The proposed method and system is validated in laboratory and field experiments. The system is deployed at coastal areas of Ariake Sea in Kyushu, Japan.
Early kick detection and nonlinear behavior of drilling mu…Frank-Michael Jäger
The following test measurements serve the quantification of resolution and achievable sensitivity of parameters of sound velocity and sound absorption in wellbore fluids. More precisely, these studies refer to tools and methods to identify the flow of liquids or gases, preferably hydrocarbons in the well bore in real time during the drilling. The aim is a way to show with the highly sensitive and robust tools for use in the deep ocean can be realized.
This document discusses air pollution engineering topics including air emissions modelling and sampling, and air pollution abatement equipment. It provides definitions of air pollution and classifications of air pollutants. It also describes common methods for air sampling and modelling to measure and estimate air pollution levels. Finally, it outlines environmental risk assessment procedures and discusses common equipment used to control and remove airborne particulates like electrostatic precipitators and fabric filters.
Cavity Ring Down Spectroscopy - CRDS: Principle, Instrumentation and ResultsHaseeb Gerraddict
The document summarizes the principles and applications of cavity ring down spectroscopy (CRDS). It describes how CRDS works by using an optical cavity to greatly increase the effective path length of light, enabling precise measurements of weak absorptions. Key applications mentioned include environmental monitoring, emissions monitoring, and trace gas analysis.
This document describes a lidar simulator system designed to study uncertainties in airborne lidar bathymetry (ALB) measurements due to light scattering in water. The simulator uses a pulsed laser beam and telescope to simulate the transmission and reception of laser pulses as they interact with a water surface and column. Preliminary results from the simulator indicate it can be used to measure the ray path of pulses through water and better understand how optical properties like diffuse attenuation affect recorded waveforms. The system aims to improve estimates of ALB measurement uncertainty under different environmental conditions.
Air quality management involves monitoring air pollutants like particulate matter, sulfur oxides, nitrogen oxides, and carbon monoxide through various sampling and analytical techniques. Key aspects include establishing air quality standards, determining emission reduction needs, and enforcing compliance through multi-level collaboration between government agencies, regulated industries, and the public. Monitoring methods like high-volume air sampling and stack sampling are used to test for suspended particulate matter, sulfur dioxide, nitrogen oxides, and carbon emissions.
Monitoring water pollution in the River Ganga with innovations in airborne remote sensing and drone technology.
Rajiv Sinha (Indian Institute of Technology Kanpur)
fr2.t03.5.2-micron IPDA Presentation at IGARSS-2011-Final-Revised-1.pptxgrssieee
This document describes the development of a high repetition rate, solid-state 2-micron pulsed laser for measuring carbon dioxide from airborne and space-based platforms. Key achievements include developing a double-pulsed, high energy 2-micron laser transmitter meeting requirements for profiling and column CO2 measurements. Ground tests demonstrated precision within 0.7% for column measurements. The laser design and performance meet requirements for direct detection pulsed integrated path differential absorption lidar for potential space-based carbon dioxide monitoring missions.
Freshwater Lake Mapping and its Volumetric Estimation in the Glaciated Valley of Chhombu in Sikkim Himalayas Using High-Resolution Optical (Sentinel-2 MSI) Imagery.
Arindam Chowdhury North Eastern Hill University, India)
Air Quality Sampling and Monitoring: Stack sampling, instrumentation and methods of analysis of SO2, CO etc, legislation for control of air pollution and automobile
pollution
It will guide to about the air sampling process which is essential step before you proceed for any type of research regarding air pollution, pollutants and health effects.
1) The document summarizes preliminary findings from using imaging spectroscopy to monitor water pollution in the Ganga River basin.
2) It outlines estimated current water quality status, the potential to detect low levels of chromium pollution, and results from a lab experiment correlating chromium concentrations with spectral signatures.
3) Future challenges include the need for consistent ground validation data and overcoming atmospheric and water chemistry complexities when analyzing hyperspectral satellite imagery of the Ganga River.
The document discusses radiometric corrections for remote sensing images. It describes how digital numbers are converted to top-of-atmosphere reflectance values using calibration coefficients and solar irradiance normalization. Atmospheric corrections are needed to estimate top-of-canopy reflectance and account for effects of gas absorption, scattering, and emission using a radiative transfer model like 6S. Parameters for the 6S model include viewing geometry, atmospheric properties, and spectral filter functions. Aerosol optical thickness can be obtained from Aeronet ground stations. Radiometric calibration is needed using reference reflectance panels.
The document describes a new algorithm for correcting the bidirectional reflectance distribution function (BRDF) of remote sensing reflectance measurements in coastal waters. Through radiative transfer simulations for a wide range of conditions, the authors developed a model relating remote sensing reflectance to the inherent optical properties of coastal waters. The new BRDF correction algorithm was shown to reduce uncertainty to below 1% when applied to both in situ and satellite ocean color data, improving on an existing open ocean algorithm. Its application significantly improved the match between in situ and MODIS satellite measurements of coastal waters.
Examination of Total Precipitable Water using MODIS measurements and Comparis...inventionjournals
This document examines the use of MODIS satellite measurements to estimate total precipitable water (TPW) and compares the results to radiosonde and GPS data. TPW was derived from MODIS near-infrared bands using established ratio techniques. Simultaneous TPW measurements from radiosonde and GPS data processing at the Mehrabad station in Iran provided points of comparison. Results showed a high correlation between TPW estimated from MODIS, radiosonde, and GPS data, validating the ability of MODIS measurements to accurately measure atmospheric water vapor content.
This document summarizes a study that measured levels of radon, thoron, and their progeny in dwellings in some areas of India over different seasons. Radon-thoron dosimeter cups containing solid state nuclear track detectors were placed in dwellings for three months periods during rainy, winter, and summer seasons. Higher average radon concentrations and annual effective doses were observed during winter compared to other seasons. Measurements were made to observe the effect of environmental conditions on radon-thoron levels throughout the year.
This document summarizes a lecture on radar clutter. It discusses different types of clutter sources including ground, sea, rain, and birds. It provides details on the attributes of rain clutter such as how it is affected by wavelength and circular polarization. Graphs are presented showing reflectivity of rain and its Doppler spectrum. Bird clutter properties around radar cross-section, velocity, and density are also covered. The document aims to explain the impact of various clutter sources on radar performance.
1) A novel photoacoustic spectrometer was developed that can measure aerosol absorption over eight wavelength bands from 300-700 nm using a single mercury arc lamp, filter wheel, and microphone.
2) Calibrations with NO2, nigrosin aerosols, and acetone demonstrated the instrument's ability to accurately measure absorption by gases and particles.
3) Measurements of nigrosin aerosol agreed with Mie theory calculations to within 7% accuracy, validating the instrument's ability to quantify aerosol absorption.
'Aerosoles, clouds and radiation' is one of the research topics of TU Delft Climate Institute. Prof Harm Jonker explained why this is so at the kick-off on March 1st 2012. Be sure to check the simulations - and more - on the YouTube channel of the Atmospheric Physics group (links included in this presentation.
Influence of chimney effect on the radon effective dose of the lung simulated...IOSR Journals
One of the well-known radon prone areas of the world is Ramsar in Iran, which is surrounded by the
Alborz Mountain in its southern part and Caspian Sea on the north. The annual effective dose in the district of
Talesh-Mahalleh is higher than the annual dose limits for radiation workers. In this study, the indoor radon
level and effective dose of the lung were estimated using a Prassi portable radon gas survey meter in a model
house containing top soil samples from different parts of Ramsar. For the extremely hot samples, the effective
dose of the lung in winter season was 27.75±2.55mSv, when the windows and exhaust part of chimney were
closed. However, when the chimney was turned on and the exhaust part of chimney was open, the effective dose
of the lung was reduced to 1.27±0.23mSv. Also the seasonal radon effective doses of the lung with other samples
were reduced to low values. The results suggest by using chimney effect and chimney heaters a significant
lessening of the radon seasonal effective dose in dwellings of Ramsar can be achieved.
Retrieval & monitoring of atmospheric green house gases (gh gs) through remot...debasishagri
- Heavier precipitation and longer/more intense droughts are effects of climate change.
- Satellite measurements of greenhouse gases like CO2, CH4, N2O can provide global coverage but require complex retrieval algorithms to account for atmospheric conditions.
- Newer retrieval techniques like using merged fitting windows have improved accuracy for scenes with thin cirrus clouds compared to earlier techniques.
“Measurements of atmospheric NO2 using a mobile DOAS system in Dhanbad, India”RAHUL GUPTA
1) The document describes a study measuring atmospheric nitrogen dioxide (NO2) using a mobile differential optical absorption spectroscopy (DOAS) system in Dhanbad, India.
2) The objectives were to characterize a portable Avantes spectrometer and use it to take NO2 measurements in Dhanbad, including at IIT(ISM) Dhanbad and the coal mining area of Jharia.
3) Preliminary results found higher NO2 levels near Jharia mines compared to IIT(ISM), but more measurements are needed to better characterize pollution levels in Dhanbad. The study of NO2 can help reduce air pollution.
Cavity Ring Down Spectroscopy - CRDS: Principle, Instrumentation and ResultsHaseeb Gerraddict
The document summarizes the principles and applications of cavity ring down spectroscopy (CRDS). It describes how CRDS works by using an optical cavity to greatly increase the effective path length of light, enabling precise measurements of weak absorptions. Key applications mentioned include environmental monitoring, emissions monitoring, and trace gas analysis.
This document describes a lidar simulator system designed to study uncertainties in airborne lidar bathymetry (ALB) measurements due to light scattering in water. The simulator uses a pulsed laser beam and telescope to simulate the transmission and reception of laser pulses as they interact with a water surface and column. Preliminary results from the simulator indicate it can be used to measure the ray path of pulses through water and better understand how optical properties like diffuse attenuation affect recorded waveforms. The system aims to improve estimates of ALB measurement uncertainty under different environmental conditions.
Air quality management involves monitoring air pollutants like particulate matter, sulfur oxides, nitrogen oxides, and carbon monoxide through various sampling and analytical techniques. Key aspects include establishing air quality standards, determining emission reduction needs, and enforcing compliance through multi-level collaboration between government agencies, regulated industries, and the public. Monitoring methods like high-volume air sampling and stack sampling are used to test for suspended particulate matter, sulfur dioxide, nitrogen oxides, and carbon emissions.
Monitoring water pollution in the River Ganga with innovations in airborne remote sensing and drone technology.
Rajiv Sinha (Indian Institute of Technology Kanpur)
fr2.t03.5.2-micron IPDA Presentation at IGARSS-2011-Final-Revised-1.pptxgrssieee
This document describes the development of a high repetition rate, solid-state 2-micron pulsed laser for measuring carbon dioxide from airborne and space-based platforms. Key achievements include developing a double-pulsed, high energy 2-micron laser transmitter meeting requirements for profiling and column CO2 measurements. Ground tests demonstrated precision within 0.7% for column measurements. The laser design and performance meet requirements for direct detection pulsed integrated path differential absorption lidar for potential space-based carbon dioxide monitoring missions.
Freshwater Lake Mapping and its Volumetric Estimation in the Glaciated Valley of Chhombu in Sikkim Himalayas Using High-Resolution Optical (Sentinel-2 MSI) Imagery.
Arindam Chowdhury North Eastern Hill University, India)
Air Quality Sampling and Monitoring: Stack sampling, instrumentation and methods of analysis of SO2, CO etc, legislation for control of air pollution and automobile
pollution
It will guide to about the air sampling process which is essential step before you proceed for any type of research regarding air pollution, pollutants and health effects.
1) The document summarizes preliminary findings from using imaging spectroscopy to monitor water pollution in the Ganga River basin.
2) It outlines estimated current water quality status, the potential to detect low levels of chromium pollution, and results from a lab experiment correlating chromium concentrations with spectral signatures.
3) Future challenges include the need for consistent ground validation data and overcoming atmospheric and water chemistry complexities when analyzing hyperspectral satellite imagery of the Ganga River.
The document discusses radiometric corrections for remote sensing images. It describes how digital numbers are converted to top-of-atmosphere reflectance values using calibration coefficients and solar irradiance normalization. Atmospheric corrections are needed to estimate top-of-canopy reflectance and account for effects of gas absorption, scattering, and emission using a radiative transfer model like 6S. Parameters for the 6S model include viewing geometry, atmospheric properties, and spectral filter functions. Aerosol optical thickness can be obtained from Aeronet ground stations. Radiometric calibration is needed using reference reflectance panels.
The document describes a new algorithm for correcting the bidirectional reflectance distribution function (BRDF) of remote sensing reflectance measurements in coastal waters. Through radiative transfer simulations for a wide range of conditions, the authors developed a model relating remote sensing reflectance to the inherent optical properties of coastal waters. The new BRDF correction algorithm was shown to reduce uncertainty to below 1% when applied to both in situ and satellite ocean color data, improving on an existing open ocean algorithm. Its application significantly improved the match between in situ and MODIS satellite measurements of coastal waters.
Examination of Total Precipitable Water using MODIS measurements and Comparis...inventionjournals
This document examines the use of MODIS satellite measurements to estimate total precipitable water (TPW) and compares the results to radiosonde and GPS data. TPW was derived from MODIS near-infrared bands using established ratio techniques. Simultaneous TPW measurements from radiosonde and GPS data processing at the Mehrabad station in Iran provided points of comparison. Results showed a high correlation between TPW estimated from MODIS, radiosonde, and GPS data, validating the ability of MODIS measurements to accurately measure atmospheric water vapor content.
This document summarizes a study that measured levels of radon, thoron, and their progeny in dwellings in some areas of India over different seasons. Radon-thoron dosimeter cups containing solid state nuclear track detectors were placed in dwellings for three months periods during rainy, winter, and summer seasons. Higher average radon concentrations and annual effective doses were observed during winter compared to other seasons. Measurements were made to observe the effect of environmental conditions on radon-thoron levels throughout the year.
This document summarizes a lecture on radar clutter. It discusses different types of clutter sources including ground, sea, rain, and birds. It provides details on the attributes of rain clutter such as how it is affected by wavelength and circular polarization. Graphs are presented showing reflectivity of rain and its Doppler spectrum. Bird clutter properties around radar cross-section, velocity, and density are also covered. The document aims to explain the impact of various clutter sources on radar performance.
1) A novel photoacoustic spectrometer was developed that can measure aerosol absorption over eight wavelength bands from 300-700 nm using a single mercury arc lamp, filter wheel, and microphone.
2) Calibrations with NO2, nigrosin aerosols, and acetone demonstrated the instrument's ability to accurately measure absorption by gases and particles.
3) Measurements of nigrosin aerosol agreed with Mie theory calculations to within 7% accuracy, validating the instrument's ability to quantify aerosol absorption.
'Aerosoles, clouds and radiation' is one of the research topics of TU Delft Climate Institute. Prof Harm Jonker explained why this is so at the kick-off on March 1st 2012. Be sure to check the simulations - and more - on the YouTube channel of the Atmospheric Physics group (links included in this presentation.
Influence of chimney effect on the radon effective dose of the lung simulated...IOSR Journals
One of the well-known radon prone areas of the world is Ramsar in Iran, which is surrounded by the
Alborz Mountain in its southern part and Caspian Sea on the north. The annual effective dose in the district of
Talesh-Mahalleh is higher than the annual dose limits for radiation workers. In this study, the indoor radon
level and effective dose of the lung were estimated using a Prassi portable radon gas survey meter in a model
house containing top soil samples from different parts of Ramsar. For the extremely hot samples, the effective
dose of the lung in winter season was 27.75±2.55mSv, when the windows and exhaust part of chimney were
closed. However, when the chimney was turned on and the exhaust part of chimney was open, the effective dose
of the lung was reduced to 1.27±0.23mSv. Also the seasonal radon effective doses of the lung with other samples
were reduced to low values. The results suggest by using chimney effect and chimney heaters a significant
lessening of the radon seasonal effective dose in dwellings of Ramsar can be achieved.
Influence of chimney effect on the radon effective dose of the lung simulated...
Similar to Ammoniak two instruments based on differential optical absorption spectroscopy (doas) to measure accurate ammonia concentrations in the atmosphere
Retrieval & monitoring of atmospheric green house gases (gh gs) through remot...debasishagri
- Heavier precipitation and longer/more intense droughts are effects of climate change.
- Satellite measurements of greenhouse gases like CO2, CH4, N2O can provide global coverage but require complex retrieval algorithms to account for atmospheric conditions.
- Newer retrieval techniques like using merged fitting windows have improved accuracy for scenes with thin cirrus clouds compared to earlier techniques.
“Measurements of atmospheric NO2 using a mobile DOAS system in Dhanbad, India”RAHUL GUPTA
1) The document describes a study measuring atmospheric nitrogen dioxide (NO2) using a mobile differential optical absorption spectroscopy (DOAS) system in Dhanbad, India.
2) The objectives were to characterize a portable Avantes spectrometer and use it to take NO2 measurements in Dhanbad, including at IIT(ISM) Dhanbad and the coal mining area of Jharia.
3) Preliminary results found higher NO2 levels near Jharia mines compared to IIT(ISM), but more measurements are needed to better characterize pollution levels in Dhanbad. The study of NO2 can help reduce air pollution.
ONLINE SCALABLE SVM ENSEMBLE LEARNING METHOD (OSSELM) FOR SPATIO-TEMPORAL AIR...IJDKP
Environmental air pollution studies fail to consider the fact that air pollution is a spatio-temporal problem.
The volume and complexity of the data have created the need to explore various machine learning models,
however, those models have advantages and disadvantages when applied to regional air pollution analysis,
furthermore, most environmental problems are global distribution problems. This research addressed
spatio-temporal problem using decentralized computational technique named Online Scalable SVM
Ensemble Learning Method (OSSELM). Evaluation criteria for computational air pollution analysis
includes: accuracy, real time & prediction, spatio-temporal and decentralised analysis, we assert that these
criteria can be improved using the proposed OSSELM. Special consideration is given to distributed
ensemble to resolve spatio-temporal data collection problem (i.e. the data collected from multiple
monitoring stations dispersed over a geographical location). Moreover, the experimental results
demonstrated that the proposed OSSELM produced impressive results compare to SVM ensemble for air
pollution analysis in Auckland region.
ONLINE SCALABLE SVM ENSEMBLE LEARNING METHOD (OSSELM) FOR SPATIO-TEMPORAL AIR...IJDKP
Environmental air pollution studies fail to consider the fact that air pollution is a spatio-temporal problem. The volume and complexity of the data have created the need to explore various machine learning models, however, those models have advantages and disadvantages when applied to regional air pollution analysis, furthermore, most environmental problems are global distribution problems. This research addressed spatio-temporal problem using decentralized computational technique named Online Scalable SVM Ensemble Learning Method (OSSELM). Evaluation criteria for computational air pollution analysis includes: accuracy, real time & prediction, spatio-temporal and decentralised analysis, we assert that these criteria can be improved using the proposed OSSELM. Special consideration is given to distributed ensemble to resolve spatio-temporal data collection problem (i.e. the data collected from multiple monitoring stations dispersed over a geographical location). Moreover, the experimental results demonstrated that the proposed OSSELM produced impressive results compare to SVM ensemble for air pollution analysis in Auckland region.
ONLINE SCALABLE SVM ENSEMBLE LEARNING METHOD (OSSELM) FOR SPATIO-TEMPORAL AIR...IJDKP
Environmental air pollution studies fail to consider the fact that air pollution is a spatio-temporal problem.
The volume and complexity of the data have created the need to explore various machine learning models,
however, those models have advantages and disadvantages when applied to regional air pollution analysis,
furthermore, most environmental problems are global distribution problems. This research addressed
spatio-temporal problem using decentralized computational technique named Online Scalable SVM
Ensemble Learning Method (OSSELM). Evaluation criteria for computational air pollution analysis
includes: accuracy, real time & prediction, spatio-temporal and decentralised analysis, we assert that these
criteria can be improved using the proposed OSSELM. Special consideration is given to distributed
ensemble to resolve spatio-temporal data collection problem (i.e. the data collected from multiple
monitoring stations dispersed over a geographical location). Moreover, the experimental results
demonstrated that the proposed OSSELM produced impressive results compare to SVM ensemble for air
pollution analysis in Auckland region.
This document discusses using artificial neural networks to estimate visibility from atmospheric and radiometric variables. A dataset of 1-minute observations of visibility, temperature, humidity, pressure, wind speed, precipitable water, direct solar irradiance, and diffuse irradiance from Huelva, Spain over 2 months was analyzed. Relative humidity was found to linearly correlate with visibility, explaining 40% of variability. Artificial neural networks improved estimation of visibility from the variables, increasing explained variability to 72% and reducing error. Including radiometric inputs provided further moderate improvements in visibility estimation.
Sampling of Atmospheric Volatile Organic Compounds (VOCS) by Muhammad Qasim, ...Muhammad Qasim
Experimental evidence collected over the last three decades has shown clearly that the accumulation in air of volatile organic compounds might represent an important source of risk for human health.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
The document analyzes the relationship between MODIS satellite measurements of aerosol optical thickness (AOT) and ground-based measurements of PM10 particulate matter concentrations in Southeastern Italy from 2006-2008. PM10 concentrations ranged from 1.6-152 μg/m3 and decreased slightly from 2006 to 2008. MODIS AOT values ranged up to 0.8 daily and 0.15-0.17 yearly. A weak linear correlation was found between daily AOT and PM10 (R=0.20-0.35), which strengthened when restricting the analysis to clear-sky MODIS measurements (R=0.34-0.57). An empirical equation was derived to estimate PM10 from clear-sky
Dynamic Stand-Alone Gas Detection SystemIRJET Journal
This document summarizes a dynamic stand-alone gas detection system designed by R.G. Dhokte and Dr. M.H. Nerkar. The system aims to flexibly detect and monitor concentrations of toxic and combustible gases like carbon monoxide, LPG and methane using low-cost sensors. An AVR microcontroller and GSM module allow for control and communication. Compared to standard systems, the results from this system's sensors are approximately equal while being more cost-effective. The system requires 16-22 minutes to provide detection results.
What does the future hold for low cost air pollution sensors? - Dr Pete EdwardsIES / IAQM
- Low-cost air pollution sensors have the potential to revolutionize air pollution measurement by enabling more widespread monitoring. However, several challenges must be addressed including sensor-to-sensor variability, complex interference from other pollutants, and factory calibrations not being applicable to real-world conditions.
- New calibration methods using machine learning algorithms that account for multivariate responses show promise in addressing these challenges. One study used support vector regression and random forest to calibrate NO and NO2 sensors, achieving accurate results with errors below 5 ppb after deployment in urban areas.
- For low-cost sensors to provide reliable data, calibration and evaluation methods must ensure data quality is sufficient for the intended application. Significant progress has been made
This document describes a study that used satellite measurements from the Cross-track Infrared Sounder (CrIS) onboard the Suomi NPP satellite to directly measure atmospheric isoprene on a global scale. The authors developed an algorithm to retrieve isoprene column abundances from CrIS spectral measurements. They applied this algorithm over the Amazon region, a major isoprene source, and found the results were consistent with model predictions and in-situ measurements, demonstrating the feasibility of direct global satellite measurements of isoprene. Combining these measurements with formaldehyde observations could help constrain atmospheric oxidation over isoprene source regions.
The document presents information on emerging technologies for air quality monitoring. It discusses various air pollutants like particulate matter, carbon monoxide, nitrogen oxides, and sulfur dioxides. It also describes different air sampling processes and the application of air quality index (AQI) to report daily air quality levels. The document outlines the objectives to analyze air quality data from pollution control boards and use sensors to provide cautionary values to alert people and improve air quality. It discusses literature review on indoor air quality and wireless sensor networks for air monitoring.
This document summarizes feasibility testing for an open-path cavity ring-down spectroscopy (CRDS) instrument to measure methane leaks from natural gas extraction and transportation. Several experiments were conducted: (1) comparing signal from ambient air vs. nitrogen gas, finding particulate scattering degraded the signal; (2) testing mirror cleanliness over time and with a purge system, finding cleanliness was maintained; (3) mobilizing the system and collecting data while driving, identifying challenges of vibrations, power needs, and ambient light shielding for mobile open-path CRDS. The research demonstrated open-path CRDS is feasible for methane leak detection despite influences of aerosols and pressure gradients, though particulate scattering and data recording during movement require
This document provides an overview of airflow in acid-generating waste rock dumps. There are three main mechanisms of airflow - diffusion, convection, and barometric pumping. Diffusion transports oxygen through concentration gradients but is limited to shallow depths. Convection occurs due to thermal or pressure gradients and can transport oxygen deeper. Barometric pumping moves air in response to atmospheric pressure changes. Understanding airflow is important to control acid rock drainage generation from waste rock.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
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2. 414 H. Volten et al.: Two DOAS instruments to measure ammonia in air
and annular denuder systems (see e.g. Wyers et al., 1993;
Van Putten et al., 1994). Such annular denuder systems
are used in the Dutch National Air Quality Monitoring Net-
work (LML) to monitor ammonia concentrations through-
out the Netherlands. They are extremely costly in main-
tenance, i.e. 15 000 C per instrument per annum. Denud-
ers were also used in a gradient set-up to obtain ammo-
nia fluxes by means of the aerodynamic gradient technique
(Wichink Kruit et al., 2007). Other methods to measure
ammonia concentrations include wet chemistry analyzers,
quantum cascade laser absorption spectroscopy, photoacous-
tic spectroscopy, and cavity ring down spectroscopy. Most
techniques are sampling techniques and therefore involve di-
rect contact with the highly adhesive ammonia resulting in
inlet problems, e.g. causing slow response times and prob-
lems with interference by ammonium aerosols dissociating
on tubes or filters (e.g. von Bobrutzki et al., 2010). This
is a severe disadvantage for process studies. Therefore, a
new system has been developed based on the open path dif-
ferential optical absorption spectroscopy (DOAS) technique.
The DOAS technique has been applied previously to measure
atmospheric ammonia concentrations by Edner et al. (1990,
1993) and Mount et al. (2002), and commercially by OPSIS
(http://opsis.se).
The RIVM DOAS system described in this paper has been
developed by the National Institute for Public Health and the
Environment (RIVM) to measure ammonia concentrations
with a fast time response. The system has a high accuracy
(typically 0.15 µg m−3 for ammonia for 5-min averages over
a total light path of 100 m), low maintenance demands and a
high up-time. Together with its fast time response, this makes
the system suitable for process studies and for other applica-
tions such as deposition measurements. However, its com-
plexity in handling, bulkiness, and building costs render it
less suitable for the use in most monitoring networks. There-
fore, a simplified second instrument, the miniDOAS, was
developed. The instrument has specifications similar to the
RIVM DOAS, but is significantly reduced in size, costs, and
handling complexity. The miniDOAS instrument is highly
suitable to be introduced in a measurement network such as
the LML.
The DOAS measurement principle is explained in Sect. 2.
Section 3 describes the instrumental designs of the RIVM
DOAS instrument and the miniDOAS. A detailed descrip-
tion of how concentration values are derived from the anal-
ysis of the measured optical absorption spectra is given in
Sect. 4. This analysis is the same for both instruments. In
Sect. 5 we present the results of laboratory tests for the RIVM
DOAS instrument, which we consider as the reference instru-
ment. We investigated the linearity of its response to NH3
and the potential interference from NO and SO2. Section 6
describes the results of a field comparison campaign con-
ducted at an LML measurement site with highly variable, but
on average high ammonia concentrations. The results of the
RIVM DOAS and miniDOAS were compared. In addition,
we compared the (mini)DOAS results with the results of the
currently used LML instrument, an annular denuder system,
AMOR (Wyers et al., 1993). We end with conclusions and
an outlook in Sect. 7.
2 Measurement method
The DOAS technique is based on the wavelength dependent
absorption of light over a specified light path. The total ex-
tinction (= absorption + scattering) is expressed by Lambert-
Beer’s law
Iλ = I0,λ · exp
− αi,λ · Ci + M + R
· L
(1)
with Iλ the received light intensity at wavelength λ, I0,λ
the emitted light intensity at wavelength λ, αi,λ the absorp-
tion coefficient for trace gas i at wavelength λ, Ci the con-
centration of trace gas i, M the extinction by small parti-
cle (Mie) scattering per unit of length, R the extinction by
Rayleigh scattering per unit of length, and L the length of
the light path. The total extinction comprises broadband ex-
tinction (Rayleigh and Mie scattering and broadband absorp-
tion) and narrowband extinction (narrowband absorption).
In the wavelength range used, from 200 nm to 230 nm, the
broadband extinction is dominated by Rayleigh scattering
and ozone absorption, and can be described by a smooth
polynomial function. After extracting the broadband extinc-
tion from an observed spectrum, a narrowband absorption
spectrum is left with absorption lines of a limited number of
gas species. A detailed description of how the concentrations
are determined from these narrowband absorption spectra is
given in Sect. 4.
Wavelength selection
The DOAS technique is often applied in the UV and visible
parts of the electromagnetic spectrum. The absorption lines
and bands of gas molecules in this part of the spectrum are
caused by electronic transitions and their shapes only weakly
depend on atmospheric temperature and pressure. Ammo-
nia has a strong absorption band with narrowband features
in the UV part of the spectrum from about 170 to 220 nm
(Chen et al., 1999). Ammonia also has lines in the IR part of
the spectrum, but in this region strong water bands may in-
terfere with the ammonia lines. Absorption by atmospheric
trace gases cannot be measured below 204 nm because of the
strong absorption by oxygen; i.e. the atmosphere is not trans-
parent below 204 nm. In the wavelength range 204–230 nm,
there is narrowband absorption only by ammonia (NH3), ni-
trogen monoxide (NO), and sulfur dioxide (SO2). Other ab-
sorbers are oxygen (O2), ozone (O3), carbon dioxide (CO2),
nitrogen dioxide (NO2), and nitrous oxide (N2O). Figure 1
shows the absorption cross sections of all these gases for
the wavelength range 200–230 nm. Data is taken from the
“MPI-Mainz-UV-VIS Spectral Atlas of Gaseous Molecules”
Atmos. Meas. Tech., 5, 413–427, 2012 www.atmos-meas-tech.net/5/413/2012/
3. H. Volten et al.: Two DOAS instruments to measure ammonia in air 415
10
-25
10
-21
10
-17
Molecular
cross
section
(cm
2
)
230
220
210
200
Wavelength (nm)
10
-21
10
-19
10
-17
SO2
NO
NH3
O3
NO2
N2O
O2
CO2
Fig. 1. Upper graph: absorption by NH3 (T = 295 K; Chen et al., 1999), NO (T = 298 K; spectrum only
partly available; Thompson et al., 1963), and SO2 (T = 293 K; Manatt and Lane, 1993). Lower graph: CO2
(T = 298 K; Shemansky, 1972), NO2 (T = 293 K; Jenouvrier et al., 1996), O3 (T = 298 K; Molina and Molina,
1986), O2 Schumann-Runge bands (T = 300 K; Yoshino et al., 1992), and O2 Herzberg continuum (T = 298 K;
Cheung et al., 1986), and N2O (T = 301 K; Selwyn et al., 1977).
17
Fig. 1. Upper graph: absorption by NH3 (T = 295 K; Chen et al.,
1999), NO (T = 298 K; spectrum only partly available; Thompson
et al., 1963), and SO2 (T = 293 K; Manatt and Lane, 1993). Lower
graph: CO2 (T = 298 K; Shemansky, 1972), NO2 (T = 293 K; Je-
nouvrier et al., 1996), O3 (T = 298 K; Molina and Molina, 1986),
O2 Schumann-Runge bands (T = 300 K; Yoshino et al., 1992), and
O2 Herzberg continuum (T = 298 K; Cheung et al., 1986), and N2O
(T = 301 K; Selwyn et al., 1977).
(Keller-Rudek and Moortgat, 2010). The NO spectrum is
only partly available in this wavelength range. From Fig. 1
it is clear that in the wavelength range 204–230 nm there is
only narrowband absorption by ammonia, nitrogen monox-
ide, sulfur dioxide and nitrogen dioxide. Therefore, a DOAS
analysis to measure ammonia in this wavelength range must
also include NO and SO2. The features from nitrogen diox-
ide (NO2) are weak at typical ambient concentrations of
around 20 ppb and not taken into account.
3 Instrument design
3.1 The RIVM DOAS instrument
The RIVM DOAS is designed to measure atmospheric am-
monia concentrations with high accuracy. Figures 2 and 3
show a schematic overview and a photograph of the in-
strument, respectively. The instrument uses a combined
sender/receiver unit (Thermo, DOAS 2000), consisting of a
150 W xenon lamp (Hamamatsu, L2273) placed in the focal
point (at 46 cm) of a 23 cm diameter Cassegrain telescope. A
corner cube retroreflector directs the lamplight directly back
to the telescope. The outer ring of the primary mirror of the
telescope is used to send the light, the inner part of the mirror
is the receiver. The retroreflector is placed at approximately
50 m from the sender/receiver unit. This results in an effec-
tive light path of approximately 100 m. The retroreflector is
heated slightly to prevent dew formation. Moisture on the
retroreflector would diminish the light gain and disturb the
measurements.
The light received by the telescope is focused by the sec-
ondary mirror and a folding mirror onto an optical fiber bun-
dle with an narrowband-pass interference filter (Newport,
G25-206-F, center wavelength 206 nm, bandwidth 26 nm
FWHM) placed in front of it. This interference filter is nec-
essary to overcome problems caused by stray light in the
spectrograph. Its center wavelength is optimal for the region
of 200 to 215 nm, where the strongest and most distinctive
spectral features of ammonia are located, but where the in-
tensity of the xenon lamp is lowest. At 200 nm the intensity
of the UV lamp is only about one hundredth of the intensity
at 400 nm and beyond. Thus, even small amounts of visible
light straying off course in the spectrograph and reaching the
detector will cause signal levels comparable to those of the
light from our wavelength region of interest. Peak transmit-
tance for this filter type is at least 20 %. The optical fiber
bundle is a spot/spot to slit line bundle assembly (see Fig. 4)
that leads the light of the telescope to the slit of a spec-
trograph (Jobin Yvon, TRIAX 320, grating 2400 lines/mm,
blaze 330 nm). Light in the wavelength-range 200–230 nm
is projected onto a charge-coupled device (CCD) detector
(Jobin Yvon, SpectrumOne/Symphony, 256 × 1024 pixels,
16 bit). The resulting wavelength mapping is 0.0306 nm per
pixel. The CCD detector is thermo-electrically cooled to sup-
press dark current. This combination of spectrograph and
CCD detector ensures a high accuracy even at low levels of
light intensity. Data is usually averaged for 5 min to increase
the signal-to-noise ratio. All system control and data storage
is managed by a computer.
The correct mapping of the different wavelengths onto the
CCD is crucial to the accuracy of the overall measurement.
This mapping, however, changes in time due to temperature
variations in the CCD and spectrograph (see Fig. 5). To pre-
vent this drift a zinc lamp is used to track the wavelengths.
The zinc lamp has a distinctive emission line at 213.84 nm
with a narrow linewidth of 0.10 nm. Its light is projected onto
the spectrograph, along with the light from the telescope.
The peak position of the zinc emission line on the CCD pixels
is determined at sub-pixel resolution with a quadratic poly-
nomial fit. This position is checked every minute. If the
position deviates by more than 0.0012 nm from the desired
position, the grating angle is micro-adjusted by a stepper mo-
tor with a resolution of 0.0010 nm. As a result, the wave-
length mapping is locked onto the CCD with an accuracy of
0.0025 nm (see Fig. 5).
The sender/receiver unit is equipped with stepper motors
to move its pointing direction. These are used to keep the
alignment between the sender/receiver unit and the retrore-
flector optimal. Every 30 min, an automated alignment pro-
cedure is executed in which the pointing direction is scanned
www.atmos-meas-tech.net/5/413/2012/ Atmos. Meas. Tech., 5, 413–427, 2012
4. 416 H. Volten et al.: Two DOAS instruments to measure ammonia in air
quartz windows
zinc
lamp spectrograph + CCD
bifurcated optical fibre
telescope
flow cell
(optional)
folding
mirror
interference
filter
xenon
lamp
50 m path
retroreflector
Fig. 2. Schematic overview of the RIVM DOAS design. The light of a xenon lamp is directed by the combined
sender/receiver telescope to a corner cube retroreflector, placed at a distance of 50 m. The light is reflected back
to the telescope by the retroreflector. With the use of two mirrors the light is focussed onto an optical fiber
that couples the light into the spectrograph followed by a CCD detector, after passing through an interference
filter. The zinc lamp with its distinctive emission peak around 213.9 nm is used for calibrating the wavelength
mapping onto the CCD. The optional flow cell is used to supply known amounts of traces gases for calibration
measurements.
18
Fig. 2. Schematic overview of the RIVM DOAS design. The light of a xenon lamp is directed by the combined sender/receiver telescope
to a corner cube retroreflector, placed at a distance of 50 m. The light is reflected back to the telescope by the retroreflector. With the
use of two mirrors the light is focussed onto an optical fiber that couples the light into the spectrograph followed by a CCD detector, after
passing through an interference filter. The zinc lamp with its distinctive emission peak around 213.9 nm is used for calibrating the wavelength
mapping onto the CCD. The optional flow cell is used to supply known amounts of traces gases for calibration measurements.
Fig. 3. Photograph of the RIVM DOAS instrument.
19
Fig. 3. Photograph of the RIVM DOAS instrument.
through a 5 × 5 grid of positions around the current direction,
in steps of 0.0075◦. For each direction, the intensity of the
reflected light is determined. The direction with the highest
intensity is chosen as the current direction for the next 30 min
measuring period. Although the accuracy of the concentra-
tion measurement during the alignment procedure is smaller,
it is still good enough for data analysis, so no measurement
time is lost.
3.2 The RIVM MiniDOAS instrument
The miniDOAS is designed to be smaller and less expen-
sive than the RIVM DOAS instrument, so that it may con-
veniently be used in an environmental monitoring network.
The main differences in design are that the sender and re-
Fig. 4. The optical fiber bundle is a spot/spot to slit line bundle assembly. The end going to the spe
consists of 47 fibers formatted into a slit line. The other end of the bundle is divided into two legs.
contains the top 3 fibers from the slit line formatted into a spot. This end leads to the zinc lamp. The ne
from the slit line are intentionally dark (dead). The other leg consists of the remaining 42 fibers form
a spot. The light of the telescope is focussed on this spot.
Fig. 4. The optical fiber bundle is a spot/spot to slit line bundle
assembly. The end going to the spectrograph consists of 47 fibers
formatted into a slit line. The other end of the bundle is divided
into two legs. One leg contains the top 3 fibers from the slit line
formatted into a spot. This end leads to the zinc lamp. The next
2 fibers from the slit line are intentionally dark (dead). The other
leg consists of the remaining 42 fibers formatted into a spot. The
light of the telescope is focussed on this spot.
ceiver are no longer combined, and that the optical fiber,
which has a transmittance of only a few percent in the UV,
has been eliminated. The spectrograph with integrated CCD
detector (Avantes AvaSpec-2048x14) used in the miniDOAS
set-up is small in size, 175 mm × 110 mm × 44 mm; it can
directly be aligned in the optical train (see Figs. 6 and 7).
Atmos. Meas. Tech., 5, 413–427, 2012 www.atmos-meas-tech.net/5/413/2012/
5. H. Volten et al.: Two DOAS instruments to measure ammonia in air 417
550.5
550.0
549.5
549.0
548.5
CCD
pixel
00:00 06:00 12:00
Elapsed time (hours)
unlocked
locked
Fig. 5. Peak position in pixels on the CCD detector of the zinc peak as function of time. The upper line shows
the zinc peak position in unlocked mode. The lower line shows the zinc peak position in locked mode. A drift
in wavelength mapping of one pixel (corresponding to 0.0306 nm) is easily reached in unlocked mode.
21
Fig. 5. Peak position in pixels on the CCD detector of the zinc peak
as function of time. The upper line shows the zinc peak position
in unlocked mode. The lower line shows the zinc peak position in
locked mode. A drift in wavelength mapping of one pixel (corre-
sponding to 0.0306 nm) is easily reached in unlocked mode.
The parabolic sender mirror is smaller (152.4 mm diameter)
than the one used in the large RIVM DOAS. The mirror is
75.4 mm deep, its focal length is 19.1 mm, which implies that
the focal point lies well within the mirror. The light of the
150 W xenon lamp (Hamamatsu, L2273) placed in the focal
point is thus more efficiently used. At 200 nm, where the re-
flectivity of the enhanced aluminium mirror coating is about
60 %, around 40 % of the total amount of light emitted by the
lamp is sent towards the retroreflector. For the RIVM DOAS
this value is only about 1.5 %.
Subsequently, we make use of the fact that the corner cube
retroreflector reflects the light directly to the sender tele-
scope, but with a slight displacement. The displacement en-
sures that some of the reflected light falls onto the receiver
parabolic mirror. Thus only a small fraction of the light re-
flected by the retroreflector is used. We can afford this lack of
efficiency, since the intensity losses in the miniDOAS are two
to three orders of magnitudes less than in the RIVM DOAS
due to a more efficient use of the lamp (40 % versus 1.5 %)
and the elimination of the optical fiber (efficiency in the UV
of only a few percent).
The received light is focussed onto the spectrograph af-
ter passing a folding mirror and the interference filter. The
spectrograph has a grating of 2400 lines/mm. The wave-
length resolution is therefore less than for the RIVM DOAS.
Light in the wavelength range 200–315 nm is projected onto
an integrated back-thinned charge CCD image sensor with
2048 × 14 pixels (16 bit). The resulting wavelength map-
ping is 0.056 nm per pixel. Because we use only the wave-
length range from 200 nm to 230 nm, about 534 × 14 pixels
are actually utilized. The lower resolution and sensitivity of
this combination of spectrograph and CCD sensor is com-
pensated by the higher light intensity levels obtained in the
RIVM miniDOAS compared to the RIVM DOAS.
Since for the miniDOAS no optical fiber is applied, we
cannot use a zinc lamp to correct for the potential drift in
the wavelength mapping onto the CCD. For this reason two
extra steps are added in the analysis of the measured results.
First, in the fitting procedure (see Sect. 2) the spectrum is
allowed to shift until a minimum in σ is reached (see Eq. 3).
Second, the signal is corrected for a fixed pattern in the CCD
response.
An automated alignment procedure as used for the large
RIVM DOAS is unnecessary for the miniDOAS, because the
spot of light coming from the sender mirror is slightly diverg-
ing and thus produces a roughly ten times larger spot falling
on the retroreflector, than for the sender of the RIVM DOAS
that produces a nearly perfectly parallel beam projecting a
spot with a diameter of 10–15 cm onto the retroreflector. The
miniDOAS is therefore not very sensitive to small changes
in the alignment of the lamp and sender mirror. In addition,
the spot of light falling on the entrance slit (with a width of
100 µm) is relatively large (about 5 × 2 mm) compared to the
spot imaged on the optical fiber bundle of the RIVM DOAS
(1 mm, with the fiber bundle diameter being 0.13 mm).
The miniDOAS instrument, excluding the retroreflector,
fits on a 75 cm by 50 cm breadboard (Fig. 7). Its total dimen-
sions are comparable to that of just the spectrograph of the
large RIVM DOAS.
4 Analysis of the optical absorption spectra
The DOAS technique is based on the wavelength dependent
absorption of light over a specified light path, with the total
extinction expressed by Lambert-Beer’s law (Eq. 1). We re-
arrange the elements in Lambert-Beer’s law to separate the
broadband extinction from the narrowband extinction
ln I0,λ/Iλ
L
= αi,λ · Ci
+ α0
i,λ · C0
i + M + R
(2)
with αi,λ and Ci denoting the absorption coefficient for and
concentration of those species with narrowband absorption,
and α0
i,λ and C0
i denoting the absorption coefficient for and
concentration of those species with broadband absorption.
The total broadband absorption (α0
i,λ · C0
i + M + R) can be
estimated by either a polynomial or a moving (boxcar) av-
erage. For our analysis a moving average over 75 channels
gives the best results. What remains is the extinction by nar-
rowband absorption.
To solve the remainder of Eq. (2), i.e. the narrowband ab-
sorption, we need to know the emitted light intensity and
the absorption spectra of the species of interest. The emitted
light intensity as a function of wavelength (Io,λ) is different
for each individual lamp and will change during its life span.
For each lamp, the emitted spectrum, unaffected by absorp-
tion from gases in the atmosphere, is measured once, using a
www.atmos-meas-tech.net/5/413/2012/ Atmos. Meas. Tech., 5, 413–427, 2012
6. 418 H. Volten et al.: Two DOAS instruments to measure ammonia in air
quartz windows
spectrograph
+ CCD
parabolic
sender
mirror
parabolic
receiver
mirror
flow cell
(optional)
folding
mirror
interference filter
xenon
lamp
50 m path
retroreflector
Fig. 6. Schematic overview of the miniDOAS design. The light of a xenon lamp is directed by the parabolic
mirror to a corner cube retroreflector, placed at a distance of 50 m. The light is reflected back to the receiving
mirror by the retroreflector. With the use of a folding mirror the light is focussed onto an spectrograph with an
integrated CCD detector, after passing through an interference filter. The flow cell is optional and is used to
supply known amounts of trace gases for calibration measurements.
22
Fig. 6. Schematic overview of the miniDOAS design. The light of a xenon lamp is directed by the parabolic mirror to a corner cube
retroreflector, placed at a distance of 50 m. The light is reflected back to the receiving mirror by the retroreflector. With the use of a folding
mirror the light is focussed onto an spectrograph with an integrated CCD detector, after passing through an interference filter. The flow cell
is optional and is used to supply known amounts of trace gases for calibration measurements.
Fig. 7. Photograph of the miniDOAS breadboard instrument.
23
Fig. 7. Photograph of the miniDOAS breadboard instrument.
short light path of 1 m, by placing the retroreflector at a dis-
tance of 50 cm. Since for real concentration measurements
the retroreflector is placed at a distance of 50 m, any gas that
is present in the atmosphere will induce an error of 1% of its
concentration during the lamp spectrum measurements. As
those measurements are performed in a well ventilated room
and ambient concentrations are expected to be low, we as-
sume that this value may be neglected. The potential spectral
changes during a lamp life span are broadband changes and
are accounted for in the moving average that is used to es-
timate the broadband extinction. The reference spectra are
absorption spectra of the species of interest (i.e. ammonia,
nitrogen monoxide and sulfur dioxide); they are measured
by supplying a known amount of trace gas in a flow cell (see
Figs. 2 and 6) placed in a short light path of about 1 m (see
Sect. 5). In addition, a measurement is performed with an
empty cell placed in the light path. This measurement is
used to correct for optical effects of the cell on the absorption
spectra. These measurements are performed for each DOAS
system individually, thereby accounting for specific instru-
ment features. For a measurement of a background spectrum,
we use BK7-glass (plain window glass) which is transparent
in the visual range down to 350 nm, but blocks all light in the
UV range. The background spectrum is subtracted from all
measured spectra. Finally, a three component least squares fit
(Kendall and Stuart, 1967) over the wavelength range 205 to
229 nm is performed to determine the concentrations of am-
monia, nitrogen monoxide and sulfur dioxide, using Eq. (3)
σ2
=
j
X
j0
Mj − α × Xj − β × Yj − γ × Zj
2
(n − 3) (3)
in which σ is the standard deviation of the fit. The wave-
length at which a measurement was performed is denoted by
j, M is the measured spectrum, n is the total number of mea-
surements, and X, Y, Z are the reference spectra for NH3,
NO, and SO2, respectively. The parameters α, β and γ are
proportional to the concentrations to be derived. The best fit
is obtained by minimizing σ2.
We found experimentally that narrowing the wavelength
range to 205–229 nm was optimal for avoiding edge effects
caused by the moving averaging, and for eliminating parts of
the spectrum that either are noisy (at the shorter wavelengths,
due to Rayleigh extinction and the onset of oxygen absorp-
tion) or do not contain absorption features (at the longer
wavelengths). An example of the different stages in the anal-
ysis is shown in Fig. 8. The residual spectrum, similar to σ,
indicates the goodness of the fit. In addition, it is a tool that
helps to identify potential flaws in the measurements, such as
interference problems.
Uncertainties in the measurements
After the fitting procedure a residual spectrum remains. This
residual is mainly due to photon noise and detector noise.
Atmos. Meas. Tech., 5, 413–427, 2012 www.atmos-meas-tech.net/5/413/2012/
7. H. Volten et al.: Two DOAS instruments to measure ammonia in air 419
10
3
10
4
10
5
230
220
210
200
Measured spectrum
1.00
0.75
0.50
230
220
210
200
Differential spectrum
-0.1
0.0
0.1
230
220
210
200
DOAS curve
0.02
0.01
0.00
-0.01
230
220
210
200
Wavelength (nm)
Residual spectrum
-40
-20
0
20
230
220
210
200
Reference spectrum NH3
-40
-20
0
20
230
220
210
200
Reference spectrum NO
-40
-20
0
20
230
220
210
200
Wavelength (nm)
Reference spectrum SO2
Fig. 8. Measurement analysis shown for a typical measurement. Left from top to bottom: measured spec-
trum (5-min average), differential spectrum (Io,λ/Iλ), DOAS curve (ln[
Io,λ/Iλ
(Io,λ/Iλ)boxcar
]), and the residual
spectrum. Right from top to bottom: NH3, NO, and SO2 reference spectra used in the fitting procedure.
Scales for the y-axes are arbitrary. Units for the reference spectra of NH3, NO, and SO2 are the same. For these
measured reference spectra the concentrations were equivalent to ambient concentrations over a path length of
100 m of 200 µg m−3
for NH3, 570 µg m−3
for NO, and 50.6 µg m−3
for SO2. The residual spectrum is plotted
in the same units as the DOAS curve. It is a tool that helps to identify potential flaws in the measurements, such
as interference problems.
24
Fig. 8. Measurement analysis shown for a typical measurement. Left from top to bottom: measured spectrum (5-min average), differential
spectrum (Iλ/I0,λ), DOAS curve (ln[
Iλ/I0,λ
(Iλ/I0,λ)boxcar
]), and the residual spectrum. Right from top to bottom: NH3, NO, and SO2 reference
spectra used in the fitting procedure. Scales for the y-axes are arbitrary. Units for the reference spectra of NH3, NO, and SO2 are the
same. For these measured reference spectra, the concentrations were equivalent to ambient concentrations over a path length of 100 m of
200 µg m−3 for NH3, 570 µg m−3 for NO, and 50.6 µg m−3 for SO2. The residual spectrum is plotted in the same units as the DOAS curve.
It is a tool that helps to identify potential flaws in the measurements, such as interference problems.
In addition, it may contain spectral features of other absorb-
ing species if these are not accounted for in the analysis.
Furthermore, the measured spectrum may contain digitiz-
ing errors because the spectral resolution of the spectrograph
is limited (0.0306 nm per pixel for the RIVM DOAS sys-
tem and 0.056 nm per pixel for the RIVM MiniDOAS sys-
tem), and because the light intensities are digitized by the
CCD (16 bit per pixel for both DOAS systems). These dig-
itizing errors will evolve throughout the analysis. The re-
maining residual spectrum determines the uncertainties in the
calculated concentrations.
Apart from instrumental specifications, another important
factor determining the uncertainty in the final concentration
measurements is the total amount of light that is reflected
onto the detector. This may, for example, depend on atmo-
spheric conditions such as haze or fog which reduces the light
intensity over the measurement path. To increase the pre-
cision in the concentration values, we average several mea-
sured spectra before analysis. For the RIVM DOAS con-
centration values, typically 200 spectra are collected and av-
eraged in a 5-min interval, which for a light path of in to-
tal 100 m results in a typical standard deviation for NH3 of
0.15 µg m−3. The miniDOAS typically collects and averages
more than 500 spectra in 1 min, which results in a typical
standard deviation of about 0.1 µg m−3 for a total light path
of 100 m.
5 Laboratory tests
The RIVM DOAS instrument has been tested in the labo-
ratory for linear response to different concentrations of am-
monia and for interference effects of nitrogen monoxide and
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8. 420 H. Volten et al.: Two DOAS instruments to measure ammonia in air
200
150
100
50
0
NH
3
measured
(µg
m
-3
)
200
150
100
50
0
NH3 offered (µg m
-3
)
Fig. 9. Results of the linearity test for the RIVM DOAS instrument. Horizontal error bars indicate estimated
errors of 5 % in the NH3 concentrations offered. Vertical error bars indicate 1-σ errors in the measured NH3
concentrations. If the error bars are not visible they are smaller than the symbol plotted.
25
Fig. 9. Results of the linearity test for the RIVM DOAS instrument.
Horizontal error bars indicate estimated errors of 5 % in the NH3
concentrations offered. Vertical error bars indicate 1-σ errors in the
measured NH3 concentrations. If the error bars are not visible they
are smaller than the symbol plotted.
-3
-2
-1
0
NH
3
retrieved
(µg
m
-3
)
600
400
200
0
NO offered (µg m
-3
)
apparent NH3 concentration
fit, y = -0.0036(6) x + 0.10(18)
Fig. 10. Results of the NO interference test for the RIVM DOAS instrument.
26
Fig. 10. Results of the NO interference test for the RIVM DOAS
instrument.
sulfur dioxide concentrations. For the linearity test, eight
NH3 concentrations between 15 ppm and 500 ppm were gen-
erated with a gas flow controller in a flow cell (Hellma,
225-QS Quartzglas Suprasil, 75 mm; see Fig. 2). Pressure
and temperature were measured during these experiments.
These concentrations yield spectra equivalent to those seen
from a 100 m path in the atmosphere, when the atmospheric
-1
0
1
NH
3
retrieved
(µg
m
-3
)
250
200
150
100
50
0
SO2 offered (µg m
-3
)
apparent NH3 concentration
fit, y = -0.000(1) x + 0.14(12)
Fig. 11. Results of the SO2 interference test for the RIVM DOAS instrument.
27
Fig. 11. Results of the SO2 interference test for the RIVM DOAS
instrument.
Fig. 12. Photo of measurement cabin with the two windows, of the RIVM DOAS (upper window, with
emerging) and the miniDOAS (lower window, partly hidden by a metal rail). The light of the lamps are dir
directly over the inlet of the AMOR instrument inside the LML measurement cabin.
Fig. 12. Photo of measurement cabin with the two windows, of
the RIVM DOAS (upper window, with light emerging) and the
miniDOAS (lower window, partly hidden by a metal rail). The light
of the lamps are directed directly over the inlet of the AMOR in-
strument inside the LML measurement cabin.
Atmos. Meas. Tech., 5, 413–427, 2012 www.atmos-meas-tech.net/5/413/2012/
9. H. Volten et al.: Two DOAS instruments to measure ammonia in air 421
350
300
250
200
150
100
50
0
NH
3
concentration
(µg
m
-3
)
16-12-2009 01-01-2010 16-01-2010 01-02-2010 18-02-2010
Date
RIVM DOAS
miniDOAS
Fig. 13. RIVM DOAS (5-min values) and miniDOAS data (1-min values) obtained in the field in Vredepeel
from 16 December 2009 to 18 February 2010.
29
Fig. 13. RIVM DOAS (5-min values) and miniDOAS data (1-min values) obtained in the field in Vredepeel from 16 December 2009 to
18 February 2010.
70
60
50
40
30
20
10
0
NH
3
concentration
(µg
m
-3
)
21 22 23 24 25 26 27
Date in December 2009
RIVM DOAS
miniDOAS
Fig. 14. Zoom in on the RIVM DOAS (5-min values) and miniDOAS data (1-min values) obtained in the field
in Vredepeel from 21 to 28 December 2009.
30
Fig. 14. Zoom in on the RIVM DOAS (5-min values) and miniDOAS data (1-min values) obtained in the field in Vredepeel from 21 to
28 December 2009.
concentrations are up to 200 µg m−3. For the conversion to
equivalent atmospheric concentrations, a pressure of 1 atmo-
sphere and a temperature of 20 ◦C was assumed. The flow
cell was positioned in the light path between the receiving
mirror and the interference filter.
It is an important advantage of the DOAS systems that
a linearity test or a span calibration procedure can be per-
formed directly with ammonia gas cylinders in the ppm
range, instead of the gas standards in the ppb range that are
needed for the calibration of instruments using sample inlet
lines. Providing gas standards in the ppb range is often only
feasible under laboratory conditions.
For the interference tests, eleven concentrations of known
amounts of nitrogen monoxide and sulfur dioxide were sup-
plied in the flow cell, in a similar way as for the ammonia lin-
earity test. For these concentrations we recorded the amount
of interference to the retrieved NH3 concentrations.
Test results
The results of the linearity test for the RIVM DOAS is shown
in Fig. 9 for equivalent atmospheric concentrations between
3 and 200 µg m−3 (1 ppb = 0.708 µg m−3 for p = 1013 hPa
and T = 20 ◦C). The linearity of the RIVM DOAS response is
excellent up to around 200 µg m−3. In the plot the combined
uncertainties in the gas flow controller and the content of the
gas cylinder have been estimated at 5 %. All data points are
on the y = x line within their error bars (see Fig. 9).
To test the potential interference by NO on the mea-
sured NH3 concentrations, we supplied NO in concentrations
equivalent to atmospheric concentrations between 13 and
600 µg m−3, and recorded the apparent NH3 concentrations.
The results are displayed in Fig. 10. A linear fit through
the data points yields y = −0.0036(6)x + 0.10(18), with the
standard deviation in the last digits indicated in parentheses.
The annual average in the Netherlands for NOx (NO + NO2)
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10. 422 H. Volten et al.: Two DOAS instruments to measure ammonia in air
70
60
50
40
30
20
10
0
NH
3
concentration
(µg
m
-3
)
00:00 06:00 12:00 18:00 00:00
Time on 24 December 2009
RIVM DOAS
miniDOAS
Fig. 15. A further zoom in on RIVM DOAS (5-min values) and miniDOAS data (1-min values) obtained in the
field in Vredepeel on 24 December 2009.
31
Fig. 15. A further zoom in on RIVM DOAS (5-min values) and miniDOAS data (1-min values) obtained in the field in Vredepeel on
24 December 2009.
200
150
100
50
0
NH
3
concentration
miniDOAS
(µg
m
-3
)
200
150
100
50
0
NH3 concentration RIVM DOAS (µg m
-3
)
miniDOAS versus RIVM DOAS
y = 0.987(1) x + 0.402(17), R
2
= 0.996
Fig. 16. Ammonia concentration values of the miniDOAS instrument versus RIVM DOAS concentration val-
ues. The miniDOAS 1-min concentrations have been converted to 5-min values to facilitate the comparison
with the 5-min concentrations of the RIVM DOAS instrument. The number of data points used in this plot
is 13 903. The results of both instruments show a high correlation (R2
= 0.996).
32
Fig. 16. Ammonia concentration values of the miniDOAS instru-
ment versus RIVM DOAS concentration values. The miniDOAS
1-min concentrations have been converted to 5-min values to
facilitate the comparison with the 5-min concentrations of the
RIVM DOAS instrument. The number of data points used in this
plot is 13 903. The results of both instruments show a high correla-
tion (R2 = 0.996).
concentrations in 2007 was 25 µg m−3 (Beijk et al., 2007). If
all this NOx would consist of NO, it would yield an inter-
ference in the NH3 concentrations of 0.01(23) µg m−3. Lo-
cally, daily or hourly values for NO may be much higher,
up to around 200 µg m−3. In these extreme cases the
interference to the measured NH3 concentrations will only
yield −0.6(2) µg m−3.
To test the potential interference by SO2 to the mea-
sured NH3 concentrations, we supplied SO2 in concentra-
tions equivalent to atmospheric concentrations between 3 and
250 µg m−3, and recorded the apparent NH3 concentrations.
The results are displayed in Fig. 11. A linear fit through the
data points yields y = −0.000(1)x + 0.14(12). SO2 concen-
trations in the Netherlands are usually low, the annual aver-
age is of the order of 2–3 µg m−3. Daily values rarely ex-
ceeded 9 µg m−3 in 2007 (Beijk et al., 2007). Therefore, in
practice SO2 interference will not be significant for DOAS
measurements.
6 Field experiments
The field measurements were performed on a LML mea-
surement station in Vredepeel (51◦3205300 N, 5◦5101100 E; see
Fig. 12). Vredepeel is located in a region in the Nether-
lands with a annual average ammonia concentration of about
17 µg m−3. The RIVM DOAS and miniDOAS instruments
were virtually continuously in operation for a period of about
two months, from 16 December 2009 to 18 February 2010
(see Fig. 13). This period included episodes with steady, rela-
tively low concentrations and episodes with rapidly-changing
high concentrations (hourly values 100 µg m−3). These
high rapidly-changing concentrations are caused by livestock
stabled in the vicinity to the northeast of the measurement
station. The results for the period of more than two months
shown in Fig. 13 illustrate that both DOAS instruments have
a high uptime.
In general, the RIVM DOAS and miniDOAS measure-
ment data agree excellently, as is illustrated in Fig. 14 which
zooms in on a week of data obtained in December 2009, and
Fig. 15 which zooms in even further to a day of data obtained
on 24 December 2009 (arbitrarily chosen). Small differences
Atmos. Meas. Tech., 5, 413–427, 2012 www.atmos-meas-tech.net/5/413/2012/
11. H. Volten et al.: Two DOAS instruments to measure ammonia in air 423
70
60
50
40
30
20
10
0
NH
3
concentration
(µg
m
-3
)
21 22 23 24 25 26 27
Date in December 2009
RIVM DOAS
miniDOAS
AMOR
Fig. 17. RIVM DOAS (5-min values), miniDOAS (1-min values), and AMOR data (1-min values) obtained in
the field in Vredepeel from 21 to 28 December 2009.
33
Fig. 17. RIVM DOAS (5-min values), miniDOAS (1-min values), and AMOR data (1-min values) obtained in the field in Vredepeel from
21 to 28 December 2009.
70
60
50
40
30
20
10
0
NH
3
concentration
(µg
m
-3
)
00:00 06:00 12:00 18:00 00:00
Time on 24 December 2009
RIVM DOAS
miniDOAS
AMOR
Fig. 18. RIVM DOAS (5-min values), miniDOAS (1-min values), and AMOR data (1-min values) obtained in
the field in Vredepeel on 24 December 2009.
34
Fig. 18. RIVM DOAS (5-min values), miniDOAS (1-min values), and AMOR data (1-min values) obtained in the field in Vredepeel on
24 December 2009.
between the two instruments are mainly due to the difference
in time resolution: the RIVM DOAS measures at 5-min in-
tervals, the miniDOAS operates at 1-min intervals. Also, the
difference in measurement height of about 1 m (see Fig. 12)
may cause slight differences in the measured ammonia con-
centrations, due to ammonia deposition or emission effects.
The scatter plot (Fig. 16) further demonstrates the ex-
cellent correlation between the RIVM DOAS and the
miniDOAS instruments. For this scatter plot, 13 903 NH3
values were used from data obtained between 18 Decem-
ber 2009 and 10 March 2010. The miniDOAS 1-min concen-
trations were converted to 5-min values to facilitate the com-
parison with the 5-min concentrations of the RIVM DOAS
instrument. A linear fit through the data points yields
y = 0.987(±0.001)x + 0.402(±0.017), and a high correlation,
R2 = 0.996.
Comparison to AMOR data
The Vredepeel station is part of the automatic atmospheric
ammonia network (Beijk et al., 2007). Ammonia is
continuously monitored with the AMOR instrument (Wyers
et al., 1993). This is a wet-chemistry system with online
analysis, also known as the AMANDA, developed by the
Energy Research Foundation of the Netherlands (ECN) that
has been adapted for use in a monitoring network (Buijs-
man et al., 1998). The presence of the AMOR at the Vre-
depeel station enabled us to compare the RIVM DOAS and
miniDOAS measurements to the AMOR measurements. In
Fig. 17 we show an example of the NH3 concentrations mea-
sured with the RIVM DOAS and the miniDOAS instruments
from 21 to 28 December 2009, compared to concentrations
measured with the AMOR instrument.
In Fig. 18 we zoom in further and we show measurements
for 24 December 2009. In addition to the RIVM DOAS and
miniDOAS data, AMOR data is plotted. Both Figs. 17 and 18
show that the AMOR curve follows the same trends as the
(mini)DOAS curves, but it is delayed in following the peaks
in the ammonia concentrations. This is a well known effect
due to the turnover time of the liquids in the continuous flow
denuder of the AMOR (e.g. von Bobrutzki et al., 2010). The
delay also smooths the signal compared to the (mini)DOAS
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12. 424 H. Volten et al.: Two DOAS instruments to measure ammonia in air
80
60
40
20
0
Average
NH
3
concentration
(µg
m
-3
)
15-12-2009 01-01-2010 15-01-2010 01-02-2010 15-02-2010
Date
RIVM DOAS
miniDOAS
AMOR
Fig. 19. Daily averaged values of RIVM DOAS, miniDOAS, and AMOR data obtained in the field in Vredepeel.
35
Fig. 19. Daily averaged values of RIVM DOAS, miniDOAS, and AMOR data obtained in the field in Vredepeel.
data. The AMOR seems to have difficulties to reach high
peaks, and, in particular, it has problems to reach very low
concentrations.
To investigate whether this behavior causes the AMOR to
produce higher values on average or whether the differences
between the AMOR and the (mini)DOAS are averaged out
when longer periods are considered, we have plotted daily
averages for the measured RIVM DOAS, miniDOAS, and
AMOR concentrations in Fig. 19. The averages over the
whole period plotted are 12.9 µg m−3 for the miniDOAS,
12.8 µg m−3 for the RIVM DOAS, and 16.3 µg m−3 for the
AMOR measurements. Overall, the AMOR averages tend
to be higher than the (mini)DOAS averages. This may be
due to an additional memory effect caused by adsorption
and desorption in the inlet lines of ammonia or ammonium
aerosols dissociating after getting stuck. Possibly, this results
in a (very slowly varying) background concentration of a few
micrograms per cubic meter.
To be able to compare the data in more detail, we calcu-
lated a running mean from the miniDOAS data using (von
Bobrutzki et al., 2010)
c0
(t) = f c(t) + (1 − f ) c0
(t − 1) (4)
where c0(t) is the delayed and smoothed concentration, c(t)
is the measured miniDOAS data and f is a smoothing factor,
which would be unity for an instrument equally fast as the
miniDOAS. To simulate the AMOR data we use an e-folding
time τ1/e of 30 min, where τ1/e = 1/f . The value of 30 min
was determined using an eye-ball fit.
In Fig. 20 we plotted the minute values of the AMOR
versus those of the miniDOAS (left panel) and the minute
values of the AMOR versus the delayed and smoothed
miniDOAS data (right panel). The linear fit, indicated in
green, changed by including the delay from y = 0.95x − 3.07
to y = 0.99x − 3.42, the coefficient of determination, R2, im-
proved significantly from 0.65 to 0.90. The fact that in the
right scatter plot the data has become organized in appar-
ent curves instead of scattered dots, probably indicates that a
more sophisticated model would produce even better agree-
ment. However, in this paper we do not aim at attaining
the best possible fit to the AMOR data, we aim at making
plausible that the differences between the AMOR and the
(mini)DOAS data are mainly due to the slower response time
of the AMOR instrument and a possible memory effect due
to ammonia stuck to inlet lines.
Figure 21 illustrates the effect of the delay and smoothing
on the miniDOAS data compared to the original miniDOAS
data and the AMOR data. We added an offset concentra-
tion to the original miniDOAS data and to the delayed and
smoothed miniDOAS data of 3.4 µg m−3, which is the dif-
ference between the miniDOAS and AMOR averages over
the whole period. The AMOR data and the delayed and
smoothed miniDOAS data are remarkably similar, indicating
again that the differences between the (mini)DOAS results
and the AMOR results are indeed mainly due to the slower
response time of the AMOR instrument and a possible mem-
ory effect due to ammonia stuck to the inlet lines. Further
small discrepancies between the AMOR data and the delayed
and smoothed miniDOAS data may be attributed to the fact
that the (mini)DOAS measures over a path of twice 50 m and
the AMOR performs point measurements. For this reason,
rapid concentration fluctuations in the air may not be seen by
both instruments in the same way.
7 Conclusions and outlook
In this paper we described two Differential Optical Absorp-
tion Spectroscopy (DOAS) instruments built at RIVM, the
RIVM DOAS and the miniDOAS. The instruments are suit-
able for the detection of NH3 concentrations in the atmo-
sphere up to at least 200 µg m−3. The instruments have no
inlet problems and no problems with interference by ammo-
nium aerosols dissociating on tubes or filters because they
measure over an open path. Laboratory tests showed that the
RIVM DOAS instrument has a linear response over a con-
centration range of a few µg m−3 up to around 200 µg m−3,
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13. H. Volten et al.: Two DOAS instruments to measure ammonia in air 425
60
40
20
0
MiniDOAS
(µg
m
-3
)
60
40
20
0
AMOR (µg m
-3
)
miniDOAS versus AMOR
fit, y = 0.95 x - 3.07, R
2
= 0.65
60
40
20
0
Delayed
miniDOAS
(µg
m
-3
)
60
40
20
0
AMOR (µg m
-3
)
delayed miniDOAS versus AMOR
y = 0.99 x - 3.42, R
2
= 0.90
Fig. 20. Scatter plots of the minute values of the AMOR versus those of the miniDOAS (left panel) and of the
minute values of the AMOR versus the delayed and smoothed miniDOAS data (right panel). Linear fits are
indicated in green, the y = x curve is plotted as a black line.
36
Fig. 20. Scatter plots of the minute values of the AMOR versus those of the miniDOAS (left panel) and of the minute values of the AMOR
versus the delayed and smoothed miniDOAS data (right panel). Linear fits are indicated in green, the y = x curve is plotted as a black line.
60
40
20
0
NH
3
concentration
(µg
m
-3
)
00:00 06:00 12:00 18:00 00:00
Time on 24 December 2009
AMOR
miniDOAS
simulated data
Fig. 21. Minute values of the miniDOAS, and the AMOR compared to delayed and smoothed miniDOAS data.
Both the miniDOAS data and the delayed and smoothed miniDOAS data have been augmented with an offset
of 3.4 µg m−3
.
37
Fig. 21. Minute values of the miniDOAS, and the AMOR compared to delayed and smoothed miniDOAS data. Both the miniDOAS data
and the delayed and smoothed miniDOAS data have been augmented with an offset of 3.4 µg m−3.
and that the potential interference by NO and SO2 at ambient
levels is small to negligible. The results of a field compari-
son campaign of more than two months indicated that both
instruments have a high uptime, and that the results of the
RIVM DOAS and the miniDOAS agree well; the scatter plot
shows a high correlation (R2 = 0.996). The agreement with
the AMOR ammonia concentrations is less perfect, but still a
very good agreement is obtained when a delay in the AMOR
system due to the turnover time of its liquids is taken into ac-
count. Daily averages of all three systems agree reasonably
well, although an offset of the AMOR values compared to the
(mini)DOAS results exists. This offset is probably caused
by three main reasons: (1) memory effects due to ammo-
nia stuck to e.g. inlet tubes; (2) ammonium aerosols stuck to
walls and inlet tubes, which eventually dissociate; and (3) a
difference of sampled air between the AMOR, which per-
forms a point measurement, and the (mini)DOAS, which per-
forms a line measurement. Alternatively, the DOAS systems
could underestimate the ammonia concentrations due to as-
sumptions made during the calibration procedure. To deter-
mine zero and span values, we use measurements over a 1 m
path assuming that the ambient ammonia contributions over
this path may be neglected. However, if the ambient concen-
tration would be high, e.g. 50 µg m−3, this would cause an
offset in the zero concentration, resulting in an underestima-
tion of the measured ammonia concentration by 0.5 µg m−3.
For the span measurements using concentrations which are
equivalent to ambient concentrations of 200 µg m−3, this ad-
ditional 0.50 µg m−3 falls within the error of the measure-
ments. In short, this potential underestimation of the DOAS
systems could explain only a small part of the discrepancy
of 3.4 µg m−3.
www.atmos-meas-tech.net/5/413/2012/ Atmos. Meas. Tech., 5, 413–427, 2012
14. 426 H. Volten et al.: Two DOAS instruments to measure ammonia in air
The relatively high variability in the ammonia concentra-
tions in Vredepeel may augment the differences between a
fast reaction instrument like the (mini)DOAS and an instru-
ment with a much slower response, such as the AMOR in-
strument. Therefore, we plan to perform further compar-
isons between the two types of instruments also on other
locations with lower and more stable concentration levels
to see if this influences the systematic differences between
the instruments.
The performance of the RIVM DOAS instrument is ex-
cellent. One of the purposes of this paper was to demon-
strate that the miniDOAS performs almost equally well, de-
spite the fact that this instrument is about a factor of ten
less costly, easier to handle, and much smaller in size. This
opens up a great number of opportunities for the applica-
tion of the miniDOAS. In the near future we will work on
an implementation plan to introduce the miniDOAS into the
Dutch National Air Quality Monitoring Network (LML) of
the Netherlands. For this purpose we will study the possi-
bilities of reducing the path length to the retroreflector from
50 m to around 10 m, and of using a smaller UV lamp pro-
ducing less heat. This would make it easier to install and
maintain the instrument at more confined measurement lo-
cations. Also, some adaptations have to be made to have
a fully automated instrument including remotely controlled
data acquisition and error handling.
Another promising application for the miniDOAS is to use
it for the measurement of ammonia fluxes, e.g. in nature ar-
eas. The relatively low cost of the instrument and the fact
that it is low on maintenance brings within reach an ammonia
flux monitoring network with high time resolution. To mea-
sure ammonia fluxes we need two miniDOAS instruments
placed at different heights, combined with a sonic anemome-
ter to measure wind speed (Wichink Kruit et al., 2010). In
particular for this application of the miniDOAS, it will be
highly desirable to design or procure a small, stable, weath-
erproof and temperature controlled housing that may be used
in masts or on open frame towers.
Acknowledgements. We are indebted to Marc Kroonen of the Ap-
plied Plant Research site in Vredepeel for his help and hospitality
during the ammonia measurement campaign. We greatly appreciate
the constructive comments from Albrecht Neftel, Arjan Hensen,
and an anonymous referee.
Edited by: P. Xie
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