Local Air Quality Monitoring Lagging Across U.S., NRDC Finds

Millions of people live in counties lacking adequate air monitoring, according to a close read of federal data.


Air quality monitoring is a key tool for helping us to understand the health dangers we face from air pollution. Harmful air pollution remains a threat in many parts of the United States (in part due to climate change–worsened ozone and wildfire smoke). To understand how exposure to air pollution affects us all, public health researchers rely on local air monitoring data.

In the United States, the landmark Clean Air Act ties air monitoring data to legal limits on pollution levels—helping the country to avoid 370,000 premature deaths annually. That landmark law has drastically reduced levels of air pollution over a half century, especially that of hazardous soot (fine particulate matter air pollution, PM 2.5), a well-documented danger to human health because of its ability to enter the lungs and bloodstream and, from there, harm our hearts, brains, and entire cardiovascular systems. According to federal data, there are currently 15 counties across the nation where soot levels exceed Clean Air Act limits; areas encompassing more than 20 million people. But NRDC has analyzed U.S. Environmental Protection Agency (EPA) data and found that there are another 8 million people exposed to unhealthy levels of soot. Given these findings, it's crucial that EPA strengthen Clean Air Act limits for soot air pollution to better protect public health.

Inadequate soot pollution monitoring across the United States

Where you burn fossil fuels, you have soot pollution. Gasoline-powered cars, coal-fired power plants—essentially any activity that involves burning coal, oil, or gas yields potentially unhealthy air. As a result, soot pollution is especially concentrated in industrial areas, which have yielded massively disproportionate exposure risks across the country. The most serious health effects have been borne by racial minorities and communities located near heavy industry. The current Clean Air Act limit for soot is 12 micrograms per cubic meter (µg/m3), a limit set forth in 2012. Since then, there has been mounting scientific evidence on the health harms from soot at even lower levels of exposure. But in 2020, the Trump EPA declined to strengthen national soot limits despite reams of data pointing to the need for stricter limits. 

Our new analysis of EPA air quality data makes clear that some counties—estimated by current models to be experiencing dangerous long-term levels of soot in the air—entirely lack monitors to track conditions on the ground. We’ve constructed a map and table, below, combining 2018 soot pollution estimates used by EPA for its last policy analysis with EPA data on the current locations of soot air monitors

This map combines modeled 2018 soot pollution levels averaged at a county level (in shades of gray, with higher pollution depicted in darker shades) with locations of soot air monitors used for Clean Air Act compliance (blue dots).

Credit: Vijay Limaye

According to our analysis, of the 190 counties with average soot levels modeled to be within current legal limits but still at unhealthy levels (ranging from 8–12 µg/m3), 118 of the counties (62 percent) completely lack a soot monitor for directly assessing Clean Air Act compliance (some have other types of air monitors used to track larger trends). As shown in the table below, this area is home to more than 8 million people. This lack of local data collection reduces the accuracy of federal air quality forecasting on AirNow and deprives people of crucial information they can use to better understand local air quality and protect their health.

2018 PM 2.5 (soot) pollution estimate (µg/m3) 0–8 8–9 9–10 10–11 11–12 12+
Number of counties 2917 counties 152 counties 22 counties 1 county 15 counties 1 county*
U.S. population (2019) 268.5 million 38.2 million 12.7 million 220,500 6.33 million 97,000*
Number of counties without at least one PM 2.5 air monitor 2396 107 7 0 4 0
U.S. population in counties without at least one PM 2.5 air monitor 107.6 million 6.86 million 1.33 million 0 139,800 0

This table depicts modeled 2018 soot pollution levels averaged at a county level; the corresponding total number of counties within each pollution range; 2019 population in those counties; counties lacking any soot monitors by pollution range; and 2019 population for those counties lacking any soot air monitors.

*These estimates are for 2018 soot pollution only; EPA currently designates 15 counties (home to 20.9 million people) in whole or partial nonattainment of the current standard of 12 (µg/m3) based on its pollution estimates spanning multiple years.

Credit: Vijay Limaye and Max López

Continuous air monitoring illuminates risks in real time 

The Government Accountability Office noted the inadequacy of current air monitoring for soot in a recent report, concluding that installation of modern, continuous air monitoring systems can improve understanding of local conditions while also reducing maintenance costs of monitors. According to that report, continuous systems tend to register higher levels of pollution than manually monitored data, and thus “provide a disincentive to switch to continuous monitoring, particularly in areas that are currently below, but close to, the National Ambient Air Quality Standards (NAAQS), according to officials from some state and local agencies.” Our analysis indicates that millions of Americans are still living in areas with unsafe levels of soot pollution. Strengthening the monitoring network is a key step toward better quantifying the harms associated with soot pollution and reducing long-standing air pollution disparities. 

The urgent need to strengthen air monitoring nationwide 

Monitoring the air and collecting data require a partnership among states (which install and maintain monitoring networks) and the federal government (which provides funding to support state and local staff and the monitoring equipment itself). But federal funding challenges have made it hard to modernize the national network. In recent years, EPA has made progress in allocating funds to soot monitoring in fenceline communities, since these places are often hit hardest by air pollution. But EPA and some states have been struggling to maintain the network of monitors that show whether counties are within legal limits, and some monitors have even been shut down recently due to strained budgets. The Inflation Reduction Act allocates significant funds to air pollution monitoring. Placing monitors in communities that suffer the most from air pollution and that currently lack monitors should be a top priority as EPA works to allocate funds from the new climate law.

The United States has made major progress in reducing air pollution over the past half century through the Clean Air Act. EPA estimates the net economic benefits of the Act to be nearly $3.8 trillion, with monetized health benefits outweighing implementation costs by a factor of more than 30 to 1. Increased investments to improve air monitoring can help leaders at the federal, state, and local levels to better understand and address current air quality problem areas. We need to improve our ability to collect data and tighten legal limits on air pollution itself to better safeguard public health across the country.

Max López contributed to this work as a Summer 2022 Stanback Fellow at NRDC.

About the Authors

Vijay Limaye

Senior Scientist, Science Office

Emily Davis

Senior Attorney, Climate & Clean Energy Program

John Walke

Director, Clean Air, Climate & Clean Energy Program

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