Monitoring exposure to tropospheric ozone precursors: AQS site evaluation and recommendation

Abstract Current air quality monitoring through the EPA’s Air Quality System (AQS) network faces significant coverage gaps particularly in vulnerable communities that experience disproportionate exposure to air pollutants. While satellite instruments provide extensive geographic coverage for monitoring tropospheric ozone (O 3 ) precursors, such as nitrogen dioxide (NO 2 ) and formaldehyde (HCHO), these space-based measurements cannot replace ground-based observations for an accurate assessment of air quality conditions near the surface. Attainment of the National Ambient Air Quality Standards for tropospheric O 3 is determined using surface measurements rather than satellite-derived column values. Using the Environmental Justice Screening and Mapping demographic and health variables, we identify underserved counties, those that lack adequate ambient air quality monitoring. We present a comprehensive method for optimizing AQS site placement by integrating satellite data from NASA’s Tropospheric Emissions: Monitoring Pollution instrument, demographic indicators, and population density. We introduce the Integrated AQS Placement Index (I IAP ), which combines normalized demographic overlap, satellite-measured HCHO or NO 2 column values, and population density to prioritize future monitoring locations. Our analysis reveals significant monitoring gaps in the Eastern and Southeastern United States, notably in the ‘isoprene volcano’ region, as well as clusters along the I-95 corridor in the Northeast. These areas are characterized by high population, high concentrations of HCHO, which is an under-monitored carcinogen, and vulnerable demographic profiles. We identify existing AQS sites that could benefit from expanded species monitoring as an economical approach to comprehensive coverage. This research underscores the critical need for proactive policies in air quality monitoring to address disparities and ensure that resources are allocated to protect the most vulnerable populations.