UNIVERSITY PARK, Pa. — In 2024, more than 50 million people in the United States lived in counties with no air-quality monitoring, according to a new study from researchers in the Penn State College of Health and Human Development.
Rural counties — especially counties in the Midwest and South — were less likely to have an air-quality monitoring site. Air quality measures are used to estimate people's exposure to air pollution, which makes monitoring a critical public health tool, according to Nelson Roque , assistant professor of human development and family studies and lead author of the study.
In an article published today (April 21) in the Proceedings of the National Academy of Sciences , the researchers examined where air quality is not monitored and which demographic and social factors were more common in unmonitored counties.
"Exposure to air pollution has been directly and indirectly to cancers, cardiovascular disease, respiratory disease, immune disorders and more," said Alexis Santos , associate professor of human development and family studies and of demography at Penn State and co-author of this study. "If we are not measuring air quality in large regions of the country, then we do not know how significant air pollution problems are. For example, if there is wildfire in a county with no air quality monitoring site, how will people know whether it is safe to sleep in their homes or work at their places of business?"
The research team analyzed data from the Environmental Protection Agency (EPA) AirData active sites directory. They found that 1,848 counties in the U.S. — 58% of all counties — have no active air-quality monitoring sites. Per-state monitoring varies greatly across the nation. Pennsylvania, for example, ranks in the top 15 states with 67% of the counties having at least one air-quality monitoring site.
By matching their data with information from the American Community Survey produced by the U.S. Census Bureau, the researchers were able to use logistic regression — a statistical model that uses available data to predict outcomes with two options — to identify which demographic and socioeconomic characteristics are more common in counties without air-quality monitoring.
The analysis revealed that rural counties were the most likely to lack monitoring sites. Additionally, when taking population size into account, the researchers found that counties without air-quality monitoring had higher levels of poverty, lower levels of high school completion, higher proportions of Hispanic residents and higher proportions of Black residents.
"Air pollution affects everyone's health, so it is important for everyone in the nation to have access to accurate information about the quality of the air they breathe," said Roque, a Social Science Research Institute co-funded faculty member. "Where we don't collect data, the threat and impact of pollution are invisible."
The nation had 4,821 active air-quality monitoring stations when the analysis was conducted, but the researchers said that the number of sites is always changing. Some monitoring sites are several decades old and frequently go offline. Between 1957 — when national air-quality monitoring began — and September 2024 — when this study was conducted — 20,815 air quality sites had been active at one point.
"We ran this same analysis just a couple months apart, and we found that the number of air-quality monitoring sites had changed over that short period of time," Roque said. "These stations are in flux all the time, and data-reporting intervals also vary, which points to the need for investment in and modernization of this infrastructure."
Air quality data is primarily gathered by the EPA or by localities in conjunction with the EPA, the researchers said.
"Generally speaking, infrastructure for health care, transportation, education and other areas are underdeveloped in rural counties," said Santos, a Social Science Research Institute co-funded faculty member. "This study demonstrated the pattern holds true for air-quality monitoring, as well. This leaves people in rural areas vulnerable to increased exposure to air pollution from wildfires, agriculture, industrial activities and other sources. As a society, we need to invest in air-quality monitoring if we want to keep people safe and save on the long-term costs of pollution exposure."
Hailey Andrews , human research technologist in the Penn State Center for Healthy Aging , contributed to this research.
The Population Research Institute, the Social Sciences Research Institute, the Data Accelerator, the Center for Healthy Aging and the College of Health and Human Development — all at Penn State — and the Einstein Aging Study supported this work.
