Geographic Variations in Urban-Rural Particulate Matter (PM 2.5 ) Concentrations in the United States, 2010-2019.

Fine particulate matter 2.5 (PM 2.5 ) is a widely studied pollutant with substantial health impacts, yet little is known about the urban-rural differences across the United States. Trends of PM 2.5 in urban and rural census tracts between 2010 and 2019 were assessed alongside sociodemographic characteristics including race/ethnicity, poverty, and age. For 2010, we identified 13,474 rural tracts and 59,065 urban tracts. In 2019, 13,462 were rural and 59,055 urban. Urban tracts had significantly higher PM 2.5 concentrations than rural tracts during this period. Levels of PM 2.5 were lower in rural tracts compared to urban and fell more rapidly in rural than urban. Rural tract annual means for 2010 and 2019 were 8.51 [2.24] μg/m 3 and 6.41 [1.29] μg/m 3 , respectively. Urban tract annual means for 2010 and 2019 were 9.56 [2.04] μg/m 3 and 7.51 [1.40] μg/m 3 , respectively. Rural and urban majority Black communities had significantly higher PM 2.5 pollution levels (10.19 [1.64] μg/m 3 and 9.79 [1.10] μg/m 3 respectively), in 2010. In 2019, they were: 7.75 [1.1] μg/m 3 and 7.09 [0.78] μg/m 3 , respectively. Majority Hispanic communities had higher PM 2.5 levels and were the highest urban concentration among all races/ethnicities (8.01 [1.73] μg/m 3 ), however they were not the highest rural concentration among all races/ethnicities (6.22 [1.60] μg/m 3 ) in 2019. Associations with higher levels of PM 2.5 were found with communities in the poorest quartile and with higher proportions of residents age<15 years old. These findings suggest greater protections for those disproportionately exposed to PM 2.5 are needed, such as, increasing the availability of low-cost air quality monitors.