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U.S. EPA’s AirNow International Air Sensor
Applications and Initiatives in Accra, Ghana
915406-6930
Alan C. Chan and Levi G. StantonSonoma Technology, Petaluma, CA, U.S.A.
Phil Dickerson, John White, and Lourdes MoralesU.S. Environmental Protection Agency, Research Triangle Park, NC, U.S.A.
Emmanuel AppohGhana Environmental Protection Agency, Accra, Ghana
for
2018 Better Air Quality ConferenceInternational Action and Cooperation on
Air Pollution Management
Kuching, MalaysiaNovember 12-16, 2018
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Outline
• Overview and Motivation
• Project Scope
• Instrument & Siting
Considerations
• Sensor Data Management
• Collocation Study
• Initial Results
• Next Steps
AirNow International Ghana
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Overview and Motivation
Many African cities lack the capacity and
cost-effective means to measure and
characterize ambient air quality to support
critical objectives.
• This work is part of the Africa
Megacities Partnership’s Air Quality
Management Planning Initiatives.
AirNow International Ghana
Air quality data gaps (source: AQICN.org)
• Ghana Environmental Protection Agency (Ghana EPA), U.S. EPA,
U.S. Department of State, and World Bank’s Pollution Management and
Environmental Health program are collaborating on this effort.
• The project includes low-cost particulate matter (PM) air sensor network
deployment and operations, infrastructure for sensor data management,
and capacity building.
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Objectives
AirNow International Ghana
• In Accra, complement the Ghana EPA’s
existing monitoring network and planned
regulatory grade monitors from the World
Bank with low-cost sensors.
• Demonstrate the feasibility/capabilities of a
PM sensor network with real-time data.
• Characterize the performance of low-cost
sensor technologies in Accra’s unique
environmental conditions.
• Integrate an advanced data system (AirNow
International) into Ghana EPA’s monitoring
and management practices, and communicate
timely air quality information to the public
(important for sensitive groups).
• Build capacity among Ghana EPA staff to
operate and analyze the data from the sensor
network.
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Project Scope
• Select sites and sensors
• Deploy sensors and conduct
sensor collocation study
• Operate sensors from August 2018
to July 2019
• Manage collected data using the
new U.S. EPA AirNow-International
system
• Interpret findings from data
• Build EPA Ghana’s real-time
monitoring capacity
AirNow International Ghana
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Instrument and Siting Considerations
AirNow International Ghana
✓ Pollutants measured
✓ Monitoring methodology
✓ Sensor performance
✓ Data handling
transparency
✓ Power requirements
✓ Communications
✓ Affordability
✓ Customer support
✓ Troubleshooting options
✓ Sites selected in consultation
with EPA Ghana
✓ Representativeness of a
variety of urban emissions
sources (near-road, industrial,
and residential)
✓ Access
✓ Security
✓ Power
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Instruments
AirNow International Ghana
• Clarity Node-S sensors (18) measure PM2.5,
temperature (T), and relative humidity (RH),
and include a battery and solar panel to
reduce the need for line power at the sites.
Sensors collect 90-second averages of PM2.5,
PM10, T, and RH about every five minutes.
Data are transmitted via cellular network.
• PurpleAir sensors (5) provide 80-second data
for PM1.0, PM2.5, and PM10 along with T, RH,
and pressure, using on-board storage.
• Campbell Scientific all-in-one MetSens600
weather stations (3) measure T, RH, pressure,
wind (speed, direction), and precipitation.
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Sensor Data Management
AirNow International Ghana
• AirNow-I system is set up in the cloud to
allow EPA Ghana to manage data collected
from the low-cost sensors, existing PM10
monitoring stations, and future sites.
– Quality control
– Email reports
– Data query and export
– Visualization and data analysis tools
• AirNow-I database provides a secure
repository, with the scalability to process
and store high-time-resolution data.
• Raw sensor measurements from the Node-
S sensors are transmitted to the Clarity
Cloud (where “Smart Calibration” is
performed) and also directly to the
AirNow-I system.
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Collocation Study
AirNow International Ghana
Collocation is performed to assess sensor
precision, accuracy, and bias.
1. All sensors and meteorological
instruments were collocated at the EPA
Ghana building for one week before being
deployed to sites.
2. Pending the upcoming deployment of
regulatory-grade PM instruments by the
World Bank program, we will collocate all
sensors with the reference instruments in
the middle of the measurement period.
3. At the end of the measurement period, all
sensors will be collocated again for
inter-comparison.
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Correlation Analysis Across all Sensors
AirNow International Ghana
A scatter plot matrix for all sensors during collocation. Darker red indicates a lower R2 (0.89 ≤ R2 ≤ 0.99). Darker
blue indicates a greater deviation of the slope from 1 (0.0≤ |1-m| ≤ 0.12).
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Initial Results
AirNow International Ghana
μg/m3
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Temporal PM2.5 Trends Across Entire Network
AirNow International Ghana
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Sensor-to-sensor correlation over study period
at four different sites (1-hr averages)
AirNow International Ghana
Black diagonal line is the 1:1 line, red diagonal line is the equation determined by
linear regression
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Next Steps
• Collocation with World Bank’s Pollution Management
and Environmental Health (PMEH) program’s
regulatory grade instruments
• Backfill of historical PM10 data
• Completion of Quality Assurance Project Plan (QAPP)
• Final data analysis
• Scientific journal paper
AirNow International Ghana
Alan C. ChanManager,
AirNow & International Programs
Levi G. StationSensor Program Lead /
Project Manager
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+1-707.665.9900 sonomatech.com @sonoma_tech
AirNow International Ghana