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/m³ and 6.41 [1.29] μg/m³, respectively. Urban tract annual means for 2010 and 2019 were 9.56 [2.04] μg/m³ and 7.51 [1.40] μg/m³, respectively. Rural and urban majority Black communities had significantly higher PM_2.5 pollution levels (10.19 [1.64] μg/m³ and 9.79 [1.10] μg/m³ respectively), in 2010. In 2019, they were: 7.75 [1.1] μg/m³ and 7.09 [0.78] μg/m³, 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/m³), however they were not the highest rural concentration among all races/ethnicities (6.22 [1.60] μg/m³) 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.