This document discusses the development and use of low-cost "PiOxide" sensors to measure carbon dioxide (CO2) concentrations in urban environments. The sensors use a Raspberry Pi microcontroller and non-dispersive infrared sensors to detect CO2 levels along with temperature, pressure, and humidity readings to increase measurement accuracy. Initial testing of the sensors found higher CO2 levels in Washington D.C.'s high traffic areas compared to parks, and demonstrated CO2 fluctuations throughout the day and week. The goal is to expand the sensor network to provide an open, citywide greenhouse gas dataset and better understand local anthropogenic impacts on CO2 domes in urban areas.

1. Kristen Caine, D. Michelle Bailey, J. Houston Miller
The George Washington University
Washington, DC 20052
Abstract
Rake and
Sampling Wire
Sensor Correction for Ambient
Conditions
Results
Urban CO2 Domes
On-Going Work
According to the EPA, carbon dioxide (CO2) accounts for 82% of all
greenhouse gas (GHG) emissions from anthropogenic sources.
CO2 contributes to increased global temperatures and thus is
causal to many environmental consequences of climate change
that negatively impact our health and welfare. In urban spaces, an
observed trend is the development of CO2 domes, characterized by
a layer of higher CO2 concentrations that are due to local
emissions. In 2014, World Bank recorded the Unites States urban
population at 81%. With the majority of Americans residing in urban
spaces it is necessary to further quantify the variability of the local
CO2 concentrations spatially and temporally. To achieve maximum
coverage and resolution, multiple ground-based measurements are
necessary. With the use of low-cost sensors developed in our
laboratory (referred to as “PiOxides”) we can record local variations
in concentration with high spatial resolution. Each PiOxide unit
utilizes a Raspberry Pi microcontroller, a non-dispersive infrared
(NDIR) sensor, and a combination pressure/temperature/humidity
sensor for the detection CO2. The inclusion of pressure and
temperature measurements increases the accuracy of the CO2
measurement. Employing PiOxides in the DC metro area would
allow us to observe emerging trends in urban GHG concentrations.
The goal is to expand sensor distribution to provide the potential for
integrative access to an urban greenhouse gas dataset and build a
citywide sensor network.
PiOxide Design
According to the IPCC from 1995 to 2005, atmospheric CO2
concentrations increased by 19 ppm, the highest average
growth rate recorded for any decade since measurements began
in the 1950s.
Credit: NOAA and NASA
The graph above shows the fluctuation in CO2 concentration over
the last 400,000 years. Prior to the 20th century the atmospheric
CO2 concentration had never surpassed 300 ppm.
In the United States, businesses and industries can take advantage of
cap and trade policies allowing them to purchase more emissions than
they are allotted. This leads to a dangerous excess of emissions in
some urban regions. These regions of increased CO2 concentration or
domes, can lead to local temperature increases which in turn increase
the amount of air pollutants and the concentration of ozone.
Washington provides an interesting living lab because it’s a commuter
city, and it is expected that carbon dioxide emissions throughout the
district would increase during the workweek compared to weekends
and even more so during primetime rush hour.
Reference: Jacobson, M. Z., 2010a: The enhancement of local air
pollution by urban CO2 domes. Environ. Sci. Technol., 44, 2497–2502,
doi:10.1021/ es903018m
Carbon Dioxide and Climate Change
The Application of Non-Dispersive IR Sensors to Detect the Variability of
Local Carbon Dioxide Concentrations in Urban Environments
PiOxide Network Expansion
Sensity Systems
GW Laser Analytics
PiOxides are also used as part of the GW laser analytics lab to
quantify greenhouse gas concentration at the Bonanza Creek
Long Term Ecological Research near Fairbanks, AK.
The sensors are based on NDIR technology. NDIR uses an infrared
(IR) light source that passes through a gas tube to an IR detector.
CO2 molecules will absorb light at specific wavelengths emitted by
the source. The intensity of this absorption behaves in accordance to
Beer's law and is monitored by tracking the decrease in power
reaching the detector.
Credit: CO2 Meter
Technical Specifications
Data Access
The PiOxide sensors transmit to an open source website
that will be accessible with both a QR code and a link to the
website.
Live PiOxide Web address: http://174.140.79.96
To quantify the effect local activities have on CO2 concentration,
measurements were averaged in two characteristically different
locations approximately 1 mile apart in the west end of
Washington, DC.
Above: This data was collected at Farragut Square. The
anthropogenic activities that characterize this high traffic region,
Farragut square, are traffic, food trucks, public transportation,
and commercial properties.
Above: The low traffic region, Dumbarton Oaks Park, was a
nature conservancy with trees and green space. This initial
research shows how local CO2 concentrations are affected by
the activities occurring around them.
The sensors require correction to produce a more accurate CO2
concentration. For pressure dependence, the sensor was placed in a
sealed container to maintain CO2 concentration and the air was
removed using a vacuum. Air was reintroduced naturally by allowing
the system to leak.
The graph above demonstrated the linearity of the relationship
between pressure and reported concentration. This technique, and
an analogous temperature experiment were used to determine the
correction factors for temperature and pressure.
Results
A PiOxide sensor was left outside in the Foggy Bottom area overnight
to further document the temporal variation of CO2 concentration.
The lowest recorded concentration was 424.1 ppm at 2:59 AM. The
highest recorded reading was 580.3 ppm at 7:55 PM demonstrating
the effect time has on CO2 concentration.
y = 0.6102x - 170.19
R² = 0.96945
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10:56:38 AM! 11:13:55 AM! 11:31:12 AM! 11:48:29 AM!12:05:46 PM!
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12:28:48! 12:36:00! 12:43:12! 12:50:24! 12:57:36! 13:04:48!
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16:48:00 19:12:00 21:36:00 0:00:00 2:24:00 4:48:00 7:12:00
CO2Reading,ppm
Time
Funding for this research project is provided by the GW Laser analy:cs Lab,
the Sigelman Undergraduate Research Enhancement, the NASA
Hydrospheric and Biospheric Science Research Program and grants-in-kind
support from 3D Robo:cs and Sensity Systems.
Carbon dioxide is an essential
GHG that contributes to
maintaining the temperature
on earth’s surface necessary
for life. When the sun shines
on the earth, the light is
reflected off Earth's surface.
Some of this reflected sunlight
escapes to space while the
rest is trapped, in the form of
heat, by the atmosphere.
Acknowledgements
Our goal is to involve the
public in climate change
research by distributing
P i O x i d e s e n s o r s t o
schools and communities.
The PiOxide network
would provide a valuable
data tool for assessing
carbon emissions in a
large, urban area.
The sensors are involved
in a collaborative project,
PA2040, an initiative to
integrate technology such
as LED streetlights,
p u b l i c l y a c c e s s i b l e
wireless internet, and an
environmental sensor
network in DC. On the
right, in blue, are the
locations where sensors
will deployed.
Our current configuration
consists of a Raspberry Pi
microcontroller, a K30 carbon
dioxide sensor, and a pressure/
temperature/humidity sensor.
The sensors detect the ambient
c o n c e n t r a t i o n o f C O 2 ,
temperature, and pressure. The
CO2 measurement is combined
with the temperature, pressure
and humidity readings to
produce a more accurate CO2
concentration.
Credit: Department of Ecology,
Washington State
Shown here is a PiOxide mounted on a 3D robotics drone that
will be used to map CO2 concentrations above a thawing
permafrost.