Radiative effect and climate impacts of brown carbon with the Community Atmosphere Model (CAM5)

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Brown, Hunter, Liu, Xiaohong, Feng, Yan, Jiang, Yiquan, Wu, Mingxuan, Lu, Zheng, Wu, Chenglai, Murphy, Shane, Pokhrel, Rudra
• Language: unknown
• Published: 2022
• Subjects: 54 ENVIRONMENTAL SCIENCES; Arctic; Aerosol Robotic Network; albedo
• Online Access: http://www.osti.gov/servlets/purl/1494669; https://www.osti.gov/biblio/1494669; https://doi.org/10.5194/acp-18-17745-2018

A recent development in the representation of aerosols in climate models isthe realization that some components of organic aerosol (OA), emitted frombiomass and biofuel burning, can have a significant contribution toshortwave radiation absorption in the atmosphere. The absorbing fraction ofOA is referred to as brown carbon (BrC). This study introduces one of thefirst implementations of BrC into the Community Atmosphere Model version 5(CAM5), using a parameterization for BrC absorptivity described in Saleh etal. (2014). Nine-year experiments are run (2003–2011) with prescribed emissionsand sea surface temperatures to analyze the effect of BrC in the atmosphere.Model validation is conducted via model comparison to single-scatter albedoand aerosol optical depth from the Aerosol Robotic Network (AERONET). Thiscomparison reveals a model underestimation of single scattering albedo (SSA) in biomass burning regionsfor both default and BrC model runs, while a comparison between AERONET andthe model absorption Ångström exponent shows a marked improvement with BrCimplementation. Global annual average radiative effects are calculated due toaerosol–radiation interaction (REari; 0.13±0.01 W m -2 )and aerosol–cloud interaction (REaci; 0.01±0.04 W m -2 ).REari is similar to other studies' estimations of BrC direct radiative effect, while REaci indicates a global reduction in low clouds due to the BrCsemi-direct effect. The mechanisms for these physical changes areinvestigated and found to correspond with changes in global circulationpatterns. Comparisons of BrC implementation approaches find that thisimplementation predicts a lower BrC REari in the Arctic regions than previousstudies with CAM5. Implementation of BrC bleaching effect shows a significantreduction in REari ( 0.06±0.008 W m -2 ). Also, variations inOA density can lead to differences in REari and REaci, indicating theimportance of specifying this property when estimating the BrC radiative effects and when comparing similar studies.