Estimation of marine dimethyl sulfide emissions from East Asian seas and their impact on natural direct radiative forcing

This study investigated the impacts of marine dimethyl sulfide (DMS) emitted from East Asian seas on natural direct radiative forcing (DRF) based on a numerical modeling approach. The high-resolution (4 km) DMS emissions (i.e., DMS flux) were estimated from sea surface DMS concentrations and transfer velocity in the air-sea interface using satellite observations and model-predicted data during the period 2014-2016. We inputted these emission data into an aerosol optical model and then estimated the natural DRF of sulfate aerosols derived from the DMS flux (i.e., DMS-derived sulfate) using a radiative transfer model. The total mean DMS flux in the study area during the study period was estimated to be approximately 0.73 mu mol/m(2)/day, with a maximum of 3.4 mu mol/m(2)/day (December 2014) and a minimum of 0.12 mu mol/m(2)/day (March 2014). The total mean negative forcing at the top of the atmosphere (DRFTOA) due to the DMS-derived sulfate was approximately -1.3 W m(-2) in the target area during the study period. The monthly maximum (-2.8 W m(-2)) and minimum DRFTOA (-0.82 W m(-2)) occurred in December and March 2014, respectively, with the highest and lowest forcing at the surface and in the atmosphere during the same months. In terms of spatial distributions over the entire study area, negative DRFTOA exhibited a maximum of up to -8.8 W m(-2) in the coastal sea near Shanghai, China, and a minimum of -0.6 Wm(-2) in the offshore sea of the East Sea, Korea. These increases and decreases in the natural DRFs were strongly attributed to the DMS fluxes, which were affected mainly by sea surface wind and/or partially by DMS concentrations, and relative humidity conditions in the study region.