Comment on acp-2022-406

Abstract

Dust aerosols affect the radiative and energy balance at local and global scales by scattering and absorbing sunlight and infrared light. Parameterizations of dust lifting, microphysics, as well as physical and radiative properties of dust in climate models are still subject to large uncertainty. Here we use a sectional aerosol model (CARMA) coupled with a climate model (CESM1) to investigate the global distribution of dust aerosols, with an emphasis on the vertical distribution of dust. Consistent with observations at locations remote from source regions, simulated dust mass size distributions peak at around 2–3 micrometres in diameter and increase by 4 orders of magnitude from 0.1 μm to 2 µm. The size distribution above 2 µm is highly variable depending on distance from the source, and subject to uncertainty due to possible size dependent changes in physical properties such as shape and density. Simulated annual mean dust mass concentrations are within one order of magnitude of those found by the surface measurement network around the globe. Simulated annual mean aerosol optical depths are ~10 % lower than AERONET observations near the dust source regions. Both simulations and in-situ measurements during the NASA ATom field campaign suggest that dust mass concentrations over the remote ocean drop by two to three orders of magnitude from the surface to the upper troposphere (200 hPa). The model suggests that Saharan, Middle Eastern, and Asian dust accounts for ~59.7 %, 12.5 %, and 13.3 % of the global annual mean dust emissions, with the remaining 14.5 % originating from scattered smaller dust sources. Although Saharan dust dominates global dust mass loading at the surface, the relative contribution of Asian dust increases with altitude and becomes dominant in the upper troposphere. The simulations show that Asian dust contributes ~60.9 % to the global and annual mean dust concentration between 266 hPa and 160 hPa. Asian dust is mostly lifted in the spring by mid-latitude frontal systems. However, deep convection during the Asian summer monsoon (ASM) favours the vertical transport of local dust to the upper atmosphere. Simulated dust accumulates in the ASM anticyclone and forms a local maximum; however, the simulated dust mass concentration is only ~0.04 % of the total aerosols in the Asian Tropopause Aerosol Layer (ATAL), which are dominated by organics, sulfates and nitrates.