Air Quality Sensor Performance Evaluation Center

Field Evaluations

  • AQMD Rubidoux-Riverside Station 2
  • AQMD Rubidoux-Riverside Station 3
  • AQMD Rubidoux-Riverside station

Commercially available "low-cost" air quality sensors are operated side-by-side with more “common” Federal Reference Methods (FRM), Federal Equivalent Methods (FEM) air monitoring equipment which is routinely used to measure the ambient concentrations of gaseous or particle pollutants for regulatory purposes or, with widely accepted best available technologies. Testing is conducted at the South Coast AQMD Rubidoux stationary ambient air monitoring station or at one of South Coast AQMD’s near-roadway sites (adjacent to the I-710 freeway). Each sensor type is field-deployed in a group of triplicate for a period of about two months to provide better compare to FRM/FEM instruments measuring the same pollutant(s) and their overall performance. A Field Testing Protocol has been developed to characterize sensor performance under ambient conditions at ambient monitoring sites in Southern California.

Several parameters are measured for evaluating the performance of a sensor technology under AQ-SPEC including:

  • Linearity: correlation (R2) between co-located sensor and FRM/FEM concentration measurements
  • Accuracy: degree of closeness of sensor concentration measurements to the actual concentration value measured using FRM/FEM instruments
  • Precision: variation around the mean of repeated measurements of the same pollutant concentration
  • Response time: how quickly does the sensor respond to changing conditions
  • Co-pollutant interference: positive or negative measurement response caused by a pollutant other than the one being measured
  • Temperature (T) and Relative Humidity (RH) influences: positive or negative measurement response caused by variations in ambient T and RH

Field Evaluation Protocol

Field Evaluation Reports

The coefficient of determination (R2) is a statistical parameter measuring the degree of relation between two variables. Here, it measures the linear relationship between the sensor and the Federal Reference Method (FRM), or Federal Equivalent Method (FEM), or Best Available Technology (BAT) reference instrument. An R2 approaching the value of 1 reflects a near perfect correlation, whereas a value of 0 indicates a complete lack of correlation. All R2 values reported in these evaluations are based either on 5-min or 1-hr average data. An ad-hoc rating system will be developed to summarize the overall performance of these sensors.


All documents, reports, data, and other information provided on this website are for informational use only. The majority of sensors evaluated as part of the Air Quality-Sensor Performance Evaluation Center (AQ-SPEC) were field-tested inside a custom-made aluminum enclosure to protect the sensors from windblown rain, harsh sunlight, and animals. The field evaluations reports included on this website contain data collected at our monitoring station during a specific 30- to 60-day period and may not be duplicated at the same or different location, season, time period, or weather conditions (e.g. temperature, relative humidity, pressure, wind speed/direction). As the overall sensor performance may be affected by the specific environmental conditions experienced at our location during the time of testing, replication and/or duplication may not be possible to achieve. The laboratory evaluation was conducted in the AQ-SPEC’s environmental chamber with simulated pollutant and interferent concentrations that were generated from nebulizer solutions, dust dispensers, and gas dilution calibrators. Generated environments may not be able to fully replicate the conditions that may be experienced under ambient settings. The sensor assembly, installation, and use can also impact the reliability of the products evaluated by AQ-SPEC. South Coast Air Quality Management District (South Coast AQMD) makes no claim, warranty, or guarantee that these devices will or will not work when operated by other users for their specific applications.

South Coast AQMD's AQ-SPEC aims at providing information to and for the benefit of the public to make informed purchasing decisions on commercially available “low cost” air quality sensor devices. In accordance with this mission, the general policy of the Governing Board of the Agency is to exclude from the AQ-SPEC website all commercial advertising and promotional material, including links which provide exclusive private or financial benefit to commercial, non-public enterprises and which do not promote or enhance a public benefit to the general public. As a Government Agency, the South Coast AQMD neither endorses nor supports individual private commercial enterprises through display of their products on the AQ-SPEC website or through providing links to the sites of such commercial enterprises.

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