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Air and Climate Change Research

Geospatial Measurements of Air Pollution (GMAP)


EPA ’s Geospatial Measurement of Air Pollution (GMAP) program designs, develops, and utilizes state of the art mobile measurement systems to gain insight into source emissions, population impacts, and exposure risk management strategies.   


GMAP uses fast-response instruments and a precise global positioning system in a mobile platform to map air pollution patterns around sources and to measure source emissions.  There are three primary GMAP applications:

GMAP Diagram showing Source Impact Monitoring (GMAP-SIM) This approach uses high resolution instruments and usually an electric vehicle to quantify the range of air pollutant concentrations around sources.  An example applications include mapping air pollutant levels on and surrounding highways, investigating the spatial variability of air pollutants and whether roadside barriers (noise walls or vegetation) modify concentrations in the near-road zone (Hagler et al., 2010).  GMAP-SIM has also recently been applied to map air pollutant concentrations surrounding a major rail yard.  GMAP-SIM studies focus on measuring a suite of air pollutants in real-time (one second data) while driving a typical speeds, allowing high resolution maps of pollutants (e.g., carbon monoxide or ultrafine particles) to be generated.  GMAP-SIM studies primarily focus on assessing the impact of a particular source on nearby populations and also the efficacy of mitigation strategies.

Remote Emission Measurement (REM)

GMAP Diagram showingTracer Correlation (GMAP-REM-TC)
The TC technique uses mobile measuring to assess emissions from  large area sources (landfills, waste water, potentially entire facilities). For this approach, a tracer gas is released and measured along with the compound of interest to yield and an emission assessment using a ratio calculation.

Direct Assessment (GMAP-REM-DA)
The DM technique provides a way to find and measure emissions from sources spread out over a large geographic area.  This approach is useful for investigating sources such as oil and gas production since DM and can be performed from public roadways without need for site access.   The measurement consists of three steps:

  1. locating emissions to be studied through drive-by inspection, keying on elevated concentrations of a surrogate compound (for example methane),
  2. estimation of surrogate emissions by combining time-resolved concentration and wind measurements from stand-off distances of 20 m to 200 m.
  3. assessment of co-emitted pollutants (such as VOCs or HAPS) by canister draw with ratio calculation.

Anticipated / Generated Impact and Products

The GMAP-SIM and GMAP-REM programs are significant innovations on air measuring research, providing information on spatial variability of air pollutants nearby sources and quantify in situ emissions factors for distributed or area sources. The GMAP-SIM work will inform the scientific and policy communities regarding the spatial extent and variability of near-source impact on air pollution. The GMAP-REM work will provide new information on emissions from relatively unknown sources, such as quantifying methane emissions from oil and gas field operations. GMAP-REM is also designing instrument packages with the intent of technology transfer to states or Regions for routine measuring work. Both GMAP-SIM and GMAP-REM are also developing software tools that may support the use of mobile measuring by research and routine measuring programs.


Hagler, G.S.W., E.D. Thoma, and R.W. Baldauf. (2010). "High-Resolution Mobile Monitoring of Carbon Monoxide and Ultrafine Particle Concentrations in a Near-Road Environment." Journal of the Air & Waste Management Association, 60:328-336.


John Masters, Communications
Phone: 919-541-0634
Email: masters.john@epa.gov
U.S. EPA National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
Mail Code: E343-02
Research Triangle Park, NC 27711

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