Drought Impacts on PM2.5 Composition and Amount Over the US During 1988–2018

Abstract

AbstractThis study uses PM2.5 species concentrations from Interagency Monitoring of Protected Visual Environments and Standardized Precipitation Evapotranspiration Index (SPEI) during 1988–2018 over the continental US to investigate the association of spatial‐temporal variations of surface PM2.5 species with droughts. Ubiquitous decreasing trends in seasonal mean reconstructed PM2.5 are detected in all seasons except for the summer over the northwestern US. The increasing trend in the reconstructed PM2.5 in summer over northwestern US is primary due to the positive trend in total carbonaceous aerosols (TCAs), which more than offsets the negative trends in sulfate and nitrate aerosols. This also causes the contribution of TCA to the reconstructed PM2.5 to show an increasing trend in summer over the same region. The positive trend in TCA in summer over northwestern US is stronger under the drought than the wet conditions, hence resulting in a stronger positive trend in the contribution of TCA to the reconstructed PM2.5 in the drought conditions. Drought enhances TCA over northwestern US through its impact on wildfire, and the temporal change of TCA mainly follows the non‐linear variation of SPEI. Although droughts are found to have statistically significant impacts on the trends in sulfate, nitrate, and dust in other regions and seasons, the small contributions of these species to the reconstructed PM2.5 make their trend variations not sufficient to affect trends in the reconstructed PM2.5.