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EPA Adds Performance Testing Protocols and Targets for NO2, CO, SO2 and PM10 Air Sensors

Updated on May 14, 2024; Originally published May 18, 2021

Ambient Air Innovation Research Site (AIRS) located on the EPA-RTP campus in Durham, NC, where EPA researchers conduct sensor evaluations.
Ambient Air Innovation Research Site (AIRS) located on the EPA-RTP campus in Durham, NC, where EPA conducts air sensor research.

Commercially available, lower-cost air sensors are a popular way to measure local air quality. Air sensors are often used by the public and researchers to understand air quality trends, study air quality in remote locations, supplement regulatory air monitoring, and support air quality education.

While there’s been a surge in their use, lower-cost sensors still pose certain challenges. Data quality from air sensors can widely vary, and, with no consistent methods to evaluate their performance, users can have a hard time knowing how their sensor data compares to that of regulatory air monitors. Users also face challenges with figuring out what sensors might best suit their desired application.

To address these issues, EPA researchers published two reports in 2021 that recommended an approach for testing and evaluating the performance of fine particulate matter (PM2.5) and ozone (O3) air sensors for use in non-regulatory supplemental and informational monitoring (NSIM) applications. EPA recently released two additional supplemental reports; one for particles with diameters of 10 microns or less (PM10) air sensors to accompany the PM2.5 report, and another for nitrogen dioxide (NO2), carbon monoxide (CO), and sulfur dioxide (SO2) air sensors to accompany the O3 report.

The supplemental reports – designed to be used by sensor manufacturers, developers, and testing organizations – provide a consistent set of testing protocols, metrics, and target values to evaluate the performance of air sensors and offer fillable templates for reporting testing results. The testing protocols are entirely voluntary, and testers do not receive certification or endorsement by EPA.

Filling a gap in air sensor guidance  

Drs. Rachelle Duvall and Andrea Clements, the EPA co-leads on this work, noted that there are already methods for testing and evaluating regulatory air monitors. Sensors, however, will likely not meet those stringent requirements. Their goal was to recommend protocols specifically for evaluating sensors used in NSIM applications, like monitoring daily and long-term air quality trends, participatory science activities, hot-spot detection, supplemental monitoring, and epidemiological studies.

“These reports are important because they offer recommendations on how to evaluate sensor performance and report the test results in a more uniform way,” Duvall said. The reports also include checklists to help testers efficiently document testing information. As a result, consumers can have greater access to detailed information related to the testing procedure, may gain better understanding of a sensor’s data quality, and make more informed decisions when selecting sensors for their application of interest.

“Having a consistent framework for documenting and reporting results will also give consumers the ability to compare the performance of different sensor technologies that measure the same pollutant,” Clements said.

Custom-built sensors operated at the Rubidoux Air Monitoring site in Riverside California (Photo Credit: South Coast Air Quality Management District)

Supplemental reports offer added benefits to consumers   

EPA originally provided testing protocols for O3 and PM2.5 air sensors only, since these sensors are the most widely used. With the supplemental reports on NO2, CO, SO2, and PM10 sensors, users will have access to more resources that can help them measure these pollutants for a variety of applications.

While lower-cost sensors sometimes advertise the ability to measure NO2, CO, SO2, and PM10, sensors on the market today often have performance issues or trouble measuring these pollutants at the low concentrations commonly found across the U.S. “Outlining specialized measurement considerations and specifying testing protocols may help manufacturers and consumers better understand the considerations needed for collecting quality measurements,” Clements explained.

Moving forward, Clements is hopeful that this work will help manufacturers communicate their air sensors’ capability and performance more consistently, which will help consumers make more informed choices. Duvall also shared her optimism about potential benefits for consumers. “I’m excited that we’re providing resources that can ultimately help all consumers, of all experience levels, better understand how sensor technologies perform and give consumers more confidence in their data quality,” she said.

For more information about EPA’s performance testing protocols, metrics, and targets reports for O3, PM2.5, NO2, CO, SO2, and PM10 air sensors, visit Air Sensor Performance Targets and Testing Protocols.

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Last updated on April 25, 2025
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