Estimating Absorption Ångström Exponent of Black Carbon Aerosol by Coupling Multiwavelength Absorption with Chemical Composition

Light absorption by black carbon (BC) and brown carbon (BrC) aerosols determines their impacts on climate warming, and the absorption Ångström exponent (AAE) attribution method often is used to distinguish the contributions of the two species to light absorption, but obtaining an accurate value for BC AAE (AAEBC) has proven challenging. In this study, a receptor model was coupled with multiwavelength absorption information for light-absorbing aerosols used to retrieve a site-dependent AAEBC that reflected the optical properties of the bulk BC aerosol. The results of a positive matrix factorization model showed that AAEBC could be separated in contributions from two BC-related factors (pure-BC and BC-rich) during the campaign, and the retrieved average AAEBC was 1.19, which is within the range of values obtained through source-related experiments and numerical calculations. The BrC light absorption estimated from AAEBC = 1.19 was significantly different from the value (i.e., AAEBC = 1.0) usually assumed in the literature. Our study provides insights that can improve the accuracy in quantifying the light absorption caused by carbonaceous aerosols, especially BrC.