Penn State Apr 21 2025 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