Impact of Brown Carbon on the Simulation of Optical Properties over East Asia in a Chemistry–climate Model

Brown carbon (BrC) has a significant impact on the climate system by absorbing light and influencing aerosol–radiation interactions. However, many chemistry-climate integrated models (CCMs) struggle to simulate BrC due to the high computational demands of modeling complex secondary organic aerosol (SOA) chemistry. To address this issue, we propose a BrC scheme integrated within a simplified SOA framework to reduce chemical and computational complexity. In this study, we applied an updated organic aerosol (OA) scheme incorporating brown carbon (BrC) in the CCM. We utilized AERONET and surface air quality observations to evaluate its impact on simulating air quality and aerosol optical properties over East Asia from 2010 to 2019. The updated OA scheme not only significantly addressed the underestimation of simulated air quality over East Asia in both summer and winter, but also reduced the negative bias in absorption aerosol optical depth (AAOD) by up to 29.17% in summer and 47.59% in winter, leading to better agreement with observations. Nevertheless, AAOD remained substantially underestimated in winter, indicating unresolved limitations. We conducted a sensitivity analysis that reflects the enhanced BrC absorption under high-NOx conditions. Accounting for the effect of NOx on BrC absorption led to a more than 50% reduction in the AAOD underestimation in both summer and winter. However, it resulted in an overestimation during the summer. These results highlight that, considering BrC absorption can significantly improve the simulation of aerosol optical properties, contributing to a better understanding of the climate’s response to aerosol–radiation interactions, particularly in East Asia.