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					      Evaluating the Use of Many Low-Cost
      Sensors for Monitoring NO2 Gradients


                           Presented by
Timothy S. Dye, David L. Vaughn, Alison E. Ray, and Paul T. Roberts
                     Sonoma Technology, Inc.
                           Petaluma, CA

      Presented at the 2010 National Air Quality Conferences
                           Raleigh, NC
                        March 15-18, 2010




                                                                3836
                 Background
• Development of citizen monitoring
  – Efforts to miniaturize and personalize
    air quality monitoring
  – Currently in the research stage
  – Several pilot projects
• Many questions remain
  – Data quality
  – Representativeness
  – Usefulness (depends on application)

                                             2
       Example – CO and NO (UK)
• Group
  – University of Cambridge (England)
• Measurement
  – CO, NO, and NO2
  – Location
• Instrument
  – Small, low-cost sensors




                                                                                            3
                                        Source: http://www.escience.cam.ac.uk/mobiledata/
Example – CO and NO (UK)




                                                                     4
                 Source: http://www.escience.cam.ac.uk/mobiledata/
Example – CO and NO (UK)

CO                      NO




                                                                     5
                 Source: http://www.escience.cam.ac.uk/mobiledata/
       Example – Carbon Monoxide
            (San Francisco)
• Group: Intel Research
• Measurements
  – CO, O3, NO2
  – Temperature and relative humidity
  – Location and light
• Instrument
  – Cell phone size
  – Solid-state sensors


• Tested on street sweepers in San Francisco
                                Source: Allison Woodruff, Intel Research   6
      Example – Carbon Monoxide
           (San Francisco)

Existing routine
CO monitoring sites
in the SF Bay Area




                                  7
     Example – Carbon Monoxide
          (San Francisco)
CO monitoring locations using street sweepers in San Francisco




                                   Source: Allison Woodruff, Intel Research   8
  EPA NO2 Sensor Feasibility Study
• Objective
     Evaluate the use of many small, low-cost NO2
     sensors to measure pollutant gradients near
     roadways
• Schedule: Now to August 2010
• Components of study
    1. Sensor characterization
    2. Field study
    3. Data analysis


                                                    9
  EPA NO2 Sensor Feasibility Study
1. Sensor characterization
  – Select sensor(s)
  – Perform simple evaluations in the laboratory
      • Zero and upscale response
      • Multi-concentration response
        (~4-5 concentration levels)
      • Repeatability
      • Response and recovery time
      • Interferences (temperature, chemical, electrical)
  – Estimate precision and accuracy
  – Determine tradeoffs between cost and quality
  – Evaluate over a range of environmental conditions
                                                            10
 EPA NO2 Sensor Feasibility Study
1. Sensor characterization




                                    11
  EPA NO2 Sensor Feasibility Study
1. Sensor characterization – our first test
                                            Intel Berkeley Sensor #21 (NO 2) Bump Test with Reference Concentrations

                             4500                                                                                                              450


                             4000                                                                                                              400


                             3500                                                                                                              350
   Sensor Output (Raw ADC)




                             3000                                                                                                              300




                                                                                                                                                     Reference Conc. (ppb)
                             2500                                                                                                              250


                             2000                                                                                                              200


                             1500                                                                                                              150


                             1000                                                                                                              100


                              500                                                                                                              50


                                0                                                                                                              0
                                    0   5     10          15            20          25            30             35             40   45   50
                                                                               Time (minutes)

                                                    Sensoric NO2 Avg Inverse    ev2 NO2 Avg Inverse    NO2 Ref        NOx Ref



                                                                                                                                                                             12
  EPA NO2 Sensor Feasibility Study
2. Field study
    –    Design sampling strategy with fixed and mobile sites
    –    Install near “anchor” or standard NO2 site
    –    Collect surface meteorological measurements
    –    Collect during a range of weather conditions

   Now           New EPA Regulation   Field Study           Citizen




                                      State/Local monitor
                                      Fixed Study Site
                                      Path of Mobile Site

                                                                      13
  EPA NO2 Sensor Feasibility Study
3. Data analysis
  – Analyze detailed NO2 and meteorological data
      • Time series analysis
      • Spatial analysis
      • Statistical analysis
  – Diagnose the spatial gradients in NO2 near roads




                                                       14
         Why Is This Important?
• Opportunity to
  –   “Fill in the gaps”
  –   Educate citizens
  –   Change behavior
  –   Engage and empower our communities
• Challenges
  – Data quality, representativeness, data use,
    formats, ownership, privacy, etc.
  – Increase coordination (for the government)

                                                  15
   Where Will We Be in 3-5 Years?
Thousands of citizens—perhaps tens of
thousands—monitoring and reporting air quality




                                                 16
   Where Will We Be in 3-5 Years?
• The “Citizen Environmental Monitoring
  Corps” is created to
  – Educate and certify citizens’ sensors
  – Empower citizens to make responsible air
    quality measurements
• “Open AIRNow” provides a framework for
  education, collaboration, and participation
  between citizens and government


                                                17

				
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