Investigation of Black Carbon Wet Deposition to the United States from National Atmospheric Deposition Network Samples

Black carbon (BC) aerosols from burning biomass, fossil fuels, and waste are transported over large distances in the Earth's atmosphere, absorbing sunlight, altering climate, and impacting air quality. These aerosols are relatively short-lived in the troposphere and are returned to the surface by wet and dry deposition processes. Although wet deposition is considered the primary mechanism for removing BC from the atmosphere, published data is exceptionally scarce. In this study, we investigated the feasibility of determining BC wet deposition on a national/international scale using samples from the US National Atmospheric Deposition Program (NADP). The study investigated BC concentrations in precipitation by single -particle laser -induced incandescence (SP2). From October 26 th to December 1 st , 2020, we analyzed 478 NADP wet deposition samples from 209 locations, including sites in the United States, Canada and US territories, Puerto Rico, and the US Virgin Islands. Wet deposition BC concentrations varied from less than 0.3 mu g L -1 to 38.7 mu g L -1 with a median of 3.50 mu g L -1 . Associated BC wet deposition fluxes ranged from near zero to 9.1 g ha -1 wk -1 , with a median of 0.87 g ha -1 wk -1 . An analysis of the spatial variability indicated a pattern of higher BC deposition through the central United States consistent with BC transport from biomass burning during the sampling period.