the presentation is about a literature review upon Aerosol optical depth, its measurement techniques and few work done with this variable in the field of environment and air pollution

1. Aerosol Optical Depth:-
A review of literature

2. Aerosols and Air Pollution
• Solid or liquid particles (in range of 0.002µm to 100µm) suspended in the
air, both natural & anthropogenic are known as aerosols.
• Aerosol particles vary greatly in size, source, chemical composition,
amount and distribution in space and time.

3. Dataset
• AOD :- AOD is the degree to which aerosol prevents
transmission of light to earth by means of scattering &
absorbing sunlight.
• An AOD of less than 0.1 indicates clear sky with
maximum visibility; whereas AOD value more than 1
indicates presence of aerosol & extinct solar radiation
reaching ground surface by absorbing or scattering.
• Depending upon their size, type, location & source of
emission, aerosols can either cool the surface (Sulfates
& Nitrates), or warm it (Black Carbon).

4. Retrieval of Aerosol Optical Depth
Data:
• AOD data can be retrieved by following means:
i. Ground based measurement
ii. Satellite data & imagery
• Ground based measurements can be carried out with:-
i. Hand-held sunphotometers which measures AOD
at 5 wavelengths (380,440,500,675 & 870 nm)
ii. Sunphotometers installed by AERONET-NASA at
selected sites
iii.CIMEL Sun-sky Radiometers

5. • Satellite data can be retrieved from the sensors on-board to
various satellites launched by NASA, which are named below:
Sensor/Platform Parameter Spatial Coverage
AVHRR/NOAA-series
• Optical Depth,
• Angstrom exponent
Daily coverage of global
ocean
TOMS/Nimbus, ADEOSI,EP • Optical Depth
Daily coverage of Global
land & ocean
POLDER,-1,-2 PARASOL
• Optical Depth,
fine mode fraction,
• Angstrom Exponent,
• Non-spherical fraction
MODIS/Terra,Aqua
• Optical Depth
• Fine-mode fraction
• Angstrom exponent
• Effective radius
MISR/Terra
• Optical depth
• Angstrom Exponent
• Small-medium-large
fraction
• Non-spherical fraction
Weekly coverage of global
land & ocean, including
bright desert

6. Review of Literature
Solomon et al (2011):-
• Investigated optical & physical characteristics of atmospheric PM
over a period of 1 year (July 2008-2009) at two sites (Bishkek &
Karakol) of Tien Shan (Central Asia)
• Objective was to evaluate impact of local source & long-range
transport of dust.
• AOD & PM2.5 – PM10 were measured using Microtops II
Sunphotometer & Automatic ambient air particulate matter
monitor 1400 TOEM respectively.
• Depending on the season, ‘r’ value varied from 0.56 to 0.87.
• Higher correlation coefficients were observed during spring &
autumn-which were revealed from the transport of Asian dust
particles & the main source was Taklimakan desert located in north-
west China.

7. Payra et al (2011):-
• Studied & measured PM concentration (0.23µm - 20µm),
meteorological parameters & atmospheric visibility in Delhi
during a winter month of year 2007-2008.
• The main objective was to show how the increase in
aerosol content & meterological parameter influences fog
formation in the northern part of India during Winter
season.
• Aerosol mass concentration was measured in 16 different
size ranges between 0.23µm - 20µm using GRIMM Aerosol
monitor & diameters were measured as Optical diameters.
• Meteorological data were retrieved from Indian
Meteorological Department.

9. Devara et al (2012);
• Investigated air pollution parameters during Diwali celebration, 8-
18 November 2012 at Pune.
• Facilities that were used were:
i. Microtops II Sunphotometer & Cimel sun-sky radiometer of
AERONET NASA for AOD meaasurement
ii. Integrated Multi-wavelength naphelometer (Ecotech, Aurora-
3000) for visibility measurement
iii. Kipp & Zonen Pyranmometer (CM21) & Eppley Model PIR
Pyrgeometer radiation sensors
iv. Automated Weather station, Dynalab WDL-1002 for recording
ambient temperature & relative humidity
v. Concurrent satellite data were also acquired for 8-18 November
2012.

10.  Spectral-Temporal variation & Influence of Meteorological parameter:

11. Variation in aerosol size & distribution:-

12.  Aerosol Direct Radiative forcing:
• The AODs and associated aerosol optical and microphysical parameters,
obtained from the Sun–sky radiometer observations during the study
period, along with other radiation and chemical parameters of aerosols
prevailing over the experimental site in the Optical Properties of Aerosols
and Clouds(OPAC) model have been used as input information to the
SantaBarbara DISORT Atmospheric Radiative Transfer (SBDART)model to
derive the aerosol direct radiative forcing (ADRF in W/m2) at the:-
i. Bottom of the atmosphere (BOA)
ii. In the atmosphere (ATM)
iii. At top of the atmosphere (TOA).

13.  Long range transport & satellite images of fire/smoke aerosols:-

14. Pandey et al (2010);
• Studied the heat island effect over metro city Delhi during months of April,
May & June – 2007,2008 & 2009.
• The study had two component:-
i. Thermal mapping of Delhi & surrounding areas
ii. Mapping of Aerosol Optical Depth
• Day & night time data for AOD & surface temperature were retrieved from
MODIS for the mentioned months.
• The images were georeferenced using ENVI software & Delhi region was
extracted from imagery. The raster data thus obtained was vectorized in
ArcGIS & then interpolated to generate map of surface temperature & AOD
over Delhi region.
• The study concluded that day time surface temperature in central part of
Delhi were significantly lower than the west & south western part. During
night-time, a distinct urban heat island formation (4-7°C elevation) with AOD
of 0.7-0.8 was observed in the central part of Delhi in all summer months.

15. Probable research gap:
• Estimation of dust re-suspension can be
carried out in order to know the impact of
local wind blown dust or vehicular emissions.
• Study on estimating the long range transport
& deposition of aerosols can be carried out.
(Long-range transport can be done using
HYSPLIT model)