Global model simulation of remote tropospheric brown carbon constrained by Atmospheric Tomography Mission (ATom) Observations

Light-absorbing aerosols significantly affect the global radiative balance and global climate by absorbing and scattering solar radiation. The light-absorbing organic carbonaceous aerosol is often referred to as brown carbon (BrC). However, the estimation of global brown carbon budget in model simulations is highly uncertain because of the lack of observation constraints and limited understanding of the physical and chemical mechanisms of BrC transport and evolution in the atmosphere. The Atmospheric Tomography Mission (ATom) provided BrC observations globally over remote regions. Here we simulated BrC in the Community Atmosphere Model version 5 (CAM5) of the Community Earth System Model (CESM) and included the photo-bleaching effect and improved deep convective transport of BrC on the basis of previous aircraft field observations. Compared to ATom measurements, we found that the model underestimated BrC concentrations, especially in the upper troposphere, indicating that the convective cloud processing of BrC is essential for understanding the global BrC distributions.