Assessing Black Carbon and Iron Oxide Aerosols: A Comparative Study between Urban and Rural Environments in the Southeastern U.S.

Black carbon (BC) and iron oxide (FeOx) aerosols represent important contributors to shortwave atmospheric heating and have been associated with adverse human health outcomes. Accurate measurement of BC and FeOx is crucial for understanding their roles in climate forcing and air quality. However, observational data─particularly for anthropogenic FeOx─remain limited. In this study, we use a modified Single Particle Soot Photometer to measure atmospheric concentrations of refractory BC (rBC) and FeOx particles in urban (Atlanta, GA) and rural (Boone, NC) environments in the southeastern U.S. We identify likely emission sources and estimate light absorption properties to assess the relative contributions of rBC and FeOx to atmospheric heating. Our findings indicate that rBC and FeOx concentrations and absorption are substantially higher in the urban environment, reflecting significant anthropogenic contributions to pollutant emissions. Assuming external mixing, we estimate that FeOx contributes 1.3% of total absorption by rBC at the urban site and approximately 0.6% at the rural site. These results highlight the spatial variability of light-absorbing aerosol components and the importance of localized assessments to better understand their impacts on air quality and climate.