In recent years, the utilization of air sensors for measuring air quality has witnessed a significant upsurge, marking a pivotal shift in how environmental conditions are monitored and understood. This increase in the deployment of air sensors has heralded progress, allowing for more localized and dynamic data collection. However, amidst this wave of advancement, a pronounced challenge remains: the variability in the quality of sensor data. This variability, ranging from exceptional to suboptimal data, poses a substantial hurdle when attempting to draw meaningful conclusions and make informed decisions based on the data generated by these sensors.
By Foster Voelker II, Director of Engineering – Williams Valve
One of the underlying factors contributing to this challenge is the absence of standardized testing methods that would otherwise facilitate a coherent assessment of the data provided by air sensors. This absence translates into a lack of consistency in the way sensor data can be compared and correlated with the outputs of established regulatory air monitoring systems. The consequences of this situation are twofold: first, it hinders the credibility and reliability of sensor data, and second, it limits the capacity to make accurate inferences from this data.
The Environmental Protection Agency (EPA) has taken steps to enhance the understanding of air sensors. One of these measures involves organizing workshops that bring together a diverse array of stakeholders. These workshops provide a platform for experts, sensor manufacturers, regulatory authorities, and other relevant parties to share their knowledge and insights. The focus of these workshops encompasses various critical aspects, including exploring the intricacies of air sensor technologies, formulating robust performance benchmarks, and gleaning lessons from similar initiatives undertaken globally.
These workshops, by addressing topics ranging from fine particulate matter (PM2.5) to ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO), provide a comprehensive perspective on the challenges and opportunities associated with air sensor deployment. The collaborative nature of these workshops facilitates the cross-pollination of ideas, nurtures a deeper understanding of the nuances within sensor technologies, and collectively informs the establishment of effective testing protocols.
To aid non-regulatory monitoring, the EPA released performance target reports in February 2021. These reports offer consistent testing protocols, metrics, and target values for evaluating air sensor performance outdoors and at fixed locations. The reports encompass field and laboratory evaluations and provide detailed guidelines for calculating performance metrics. The reports intend to benefit testing organizations, sensor manufacturers, and various consumers, aiding in selecting suitable sensor technologies and comprehending their performance.
Ozone Sensor Report
This report aims to establish standardized testing procedures, metrics, and target values for assessing ozone air sensor performance in non-regulatory supplemental and informational monitoring (NSIM) scenarios in outdoor, fixed-site environments. It suggests two testing protocols: base testing and enhanced testing, with a recommendation for all testers to undertake base testing and encourages enhanced testing using laboratory exposure chambers.
The report identifies performance metrics and target values based on current scientific understanding, literature reviews, evaluations by other organizations, ongoing sensor standardization initiatives, and U.S. EPA sensor research expertise. These are summarized in tables within the report. For base testing, an additional data visualization termed ‘exploring meteorological effects’ is suggested, involving graphing meteorological data’s impact on sensor performance. The report advises having at least one day during base testing with a one-hour average O3 concentration of 60 parts per billion by volume (ppbv) or more at the test site(s).
Further performance metrics and test conditions for enhanced testing are detailed. The report explains how to calculate performance metrics for O3 sensors and offers templates for both base and enhanced testing reports for consistent result presentation. Notably, target values for enhanced testing are omitted due to limited feasibility and data constraints.
The report acknowledges the evolving nature of O3 sensor technologies and anticipates updating the provided information as advances occur. The report’s audience includes potential testing bodies, sensor manufacturers, and developers. Various consumers such as government agencies, community groups, and academia are expected to benefit from the standardized presentation of testing results. However, testing outcomes do not imply U.S. EPA certification or endorsement, and testers are encouraged to make their reports public to inform consumers.
Similar to the ozone report, the objective of this report is to establish standardized testing methods, metrics, and target values for the comprehensive evaluation of PM2.5 air sensors. Specifically, the focus is on their performance within the realm of NSIM applications, primarily conducted in outdoor, fixed-site environments. Within this context, the report delineates two distinct testing protocols: base testing and enhanced testing. It strongly encourages all practitioners to undertake the foundational base testing, while also proposing the adoption of enhanced testing using controlled laboratory exposure chambers, particularly in scenarios characterized by elevated PM2.5 concentrations, such as those encountered during wildfire smoke incidents.
The report derives its performance metrics and corresponding target values through an amalgamation of multiple sources. These include current scientific understanding, comprehensive literature reviews, evaluations conducted by reputable external organizations, the ongoing endeavors of sensor standardization programs, and the invaluable expertise amassed by the U.S. EPA in the realm of sensor evaluation research.
These metrics and targets are summarized in tables. For base testing, an ‘exploring meteorological effects’ data visualization is suggested to graph meteorological data’s impact on sensor performance. Additionally, the report recommends having at least one day of base testing with a 24-hour average PM2.5 concentration of 25 micrograms per cubic meter (μg/m³) or higher at the test sites.
Additional performance metrics and test conditions for enhanced testing are provided. The report explains how to calculate performance metrics for PM2.5 sensors and includes templates for base and enhanced testing reports to ensure consistent result reporting. However, as in the ozone report, target values for enhanced testing are omitted due to feasibility constraints and variations in sensor evaluation outcomes based on limited data collection and PM surrogate selection.
Acknowledging the continuous improvement of PM2.5 sensor technologies, the report anticipates updating the provided information to reflect advancements in the field and new knowledge gained from sensor evaluations. The report’s target audience includes potential testing organizations, sensor manufacturers, and developers. Various consumers, such as government agencies, community groups, and academia, are expected to benefit from standardized testing result presentations. Again, however, it is emphasized that testing outcomes do not signify U.S. EPA certification or endorsement, and testers are encouraged to share their reports on their websites to inform consumers.
The proliferation of air sensors for assessing air quality has ushered in a new era of monitoring environmental conditions. This surge in sensor deployment has led to valuable localized data collection. However, the challenge of varying data quality remains a significant hurdle. The absence of standardized testing methods impedes the effective comparison of sensor data with regulatory air monitoring outputs, impacting data credibility and decision-making.
To address these challenges, the EPA has initiated workshops involving experts, manufacturers, and regulators. These workshops delve into air sensor technologies, performance benchmarks, and lessons from similar projects, encompassing pollutants such as PM2.5, O3, NO2, SO2, and CO. To aid non-regulatory monitoring, the EPA released performance target reports with consistent testing protocols, metrics, and target values for assessing air sensor efficacy in outdoor and fixed locations.
The report focusing on ozone sensors seeks to establish standardized testing methods, performance metrics, and target values for non-regulatory air quality monitoring. It introduces base and enhanced testing protocols, outlining performance metrics and advising on base testing conditions. It acknowledges the evolving nature of ozone sensor technologies and emphasizes the report’s utility for potential testers, manufacturers, and consumers. A similar report targeting PM2.5 sensors establishes testing protocols, metrics, and base testing conditions. It highlights the importance of meteorological effects on sensor performance and encourages enhanced testing for specific scenarios. Both reports anticipate regular updates to reflect advancements and underline that testing outcomes do not imply EPA certification or endorsement. The dissemination of testing results is encouraged to inform consumers.
- Duvall, R., A. Clements, G. Hagler, A. Kamal, Vasu Kilaru, L. Goodman, S. Frederick, K. Johnson Barkjohn, I. VonWald, D. Greene, AND T. Dye. Performance Testing Protocols, Metrics, and Target Values for Ozone Air Sensors: Use in Ambient, Outdoor, Fixed Site, Non-Regulatory and Informational Monitoring Applications. U.S. EPA Office of Research and Development, Washington, DC, EPA/600/R-20/279, 2021.
- Duvall, R., A. Clements, G. Hagler, A. Kamal, Vasu Kilaru, L. Goodman, S. Frederick, K. Johnson Barkjohn, I. VonWald, D. Greene, AND T. Dye. Performance Testing Protocols, Metrics, and Target Values for Fine Particulate Matter Air Sensors: Use in Ambient, Outdoor, Fixed Site, Non-Regulatory Supplemental and Informational Monitoring Applications. U.S. EPA Office of Research and Development, Washington, DC, EPA/600/R-20/280, 2021.