Long-term evolution and effects of primary brown carbon aerosol in China

Abstract. Brown carbon (BrC) is a light-absorbing component of organic aerosols that influences atmospheric environment and climate. Although, biomass burning is recognized as the major source of primary BrC (PBrC) globally anthropogenic sources can contribute comparably or more to PBrC in regions with intensive human activities, yet variations in concentrations and effects of PBrC remain underexplored in China where dramatic emission changes occurred in last two decades. We apply an internal mixing model to simulate the long-term (2005–2020) variations of PBrC surface and vertical concentrations and their effects across China. The mean surface PBrC concentration is 0.81 μgC m-3, with anthropogenic emissions dominating: residential, industrial combustion, and agricultural sectors contribute on average 57 %, 22 %, and 18 %, respectively, together accounting for 91 % of column concentrations in 2010. PBrC (-20.8 %) declined more than PM2.5 (-8.1 %), accompanied by a slight reduction in O3 and a decrease in direct radiative effect (DRE) from +0.032 W m-2 in 2005 to +0.023 W m-2 in 2020 (-25.7 %), with anthropogenic sources contributing 84.2 % of total DRE. This study provides the first long-term assessment of PBrC trends, sources, and radiative effects in human-dominated regions, demonstrating that emission controls can deliver both environment and climate co-benefits.