Air Quality Sensor Performance Evaluation Center

Mobile Sensors

South Coast AQMD partnership with Google for Mobile Sensing Project

The Air Quality Sensor Performance Evaluation Center (AQ-SPEC) at South Coast AQMD began a partnership with Google Earth Outreach to test the performance of low-cost sensors on moving vehicles. As part of this project, low-cost sensors collected measurements of ambient air on a Google Street View car driving through different locations.

A prominent outcome of this collaboration is the development of the first-ever performance evaluation protocol for low-cost sensors deployed on a moving vehicle. The protocol tests the agreement between reference-grade instruments and low-cost sensors mounted in various scenarios, such as inside a rooftop box. The full protocol is available here.

This protocol was pilot-tested with different low-cost sensor models, and the testing process revealed information that would be useful to organizations and individuals looking to use such sensors for mobile monitoring. For example, one of the low-cost sensors was found to be greatly affected by driving speed when mounted on the vehicle rooftop and completely exposed; however, by placing the low-cost sensor inside of a box to partially shield it from turbulent winds while moving, the low-cost sensor was found to have better agreement with readings from the reference-grade instrument. The pilot-testing also found that the correlation and accuracy of low-cost sensor measurements varies with driving speed, and that driving on local roads slowly can provide better measurements than those collected while driving on freeways at high speeds. The results of pilot-testing this novel evaluation protocol were published in Environmental Science and Technology as an open-access article (

The project is intended to analyze the potential and limitations of low-cost air monitoring sensors for measuring fine particulate matter (PM2.5), ozone (O3) and other air pollutants and determine which types may be best suited for mobile uses.

Figure 1. Google Street View Car at South Coast AQMD's AQ-SPEC

AQ-SPEC has been conducting stationary field and laboratory testing of commercially available low-cost sensors since 2014, and this new project will provide additional information on the performance of low-cost sensors when used in mobile monitoring applications. A protocol with best practices for conducting mobile monitoring using sensors has been developed as part of this collaboration with Google. This will be particularly important for community scientists and groups that are interested in conducting measurement surveys at the neighborhood level.

Figure 2. Example of a test route for the performance evaluation of low-cost sensors for measuring PM2.5 (on the left) and NO2 (on the right). Measurements were conducted on board of a Google Street View car in the Wilmington/West Long Beach/Carson area on August 26, 2019.santafemap2

Mobile sensors gathering street level data will allow collection of more air pollution information over a much larger area than traditional air monitoring technologies that stay in one location. These mobile measurements are expected to demonstrate how much pollution can change over very short distances, such as a city block or throughout a neighborhood.

Given their comparatively low-cost compared to traditional fixed-site equipment, when proven to be accurate and reliable, mobile sensors could also become useful tools for introducing students to air quality issues, and for environmental groups and individuals to independently evaluate air quality.

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