Global trend analysis in primary and secondary production of marine aerosol and aerosol optical depth during 2000-2015.

The global trends in sea spray aerosol (SSA) emissions, dimethyl sulfide (DMS) flux from sea to air, and aerosol optical depth (AOD) during 2000-2015 were analyzed using the satellite-based, ECMWF reanalysis, and model-predicted data. The SSA emissions were estimated using a widely used whitecap method with a sea surface temperature (SST) dependence. The sea-to-air DMS fluxes were estimated by a thin film model based on the DMS concentration in seawater and its gas transfer velocity. The yearly global mean anomaly in DMS fluxes showed a significant downward trend during the study period, whereas the SSA emissions showed an upward trend. In terms of regional trends, the increases in SSA emissions during 2000-2015 occurred over the tropical southeastern Pacific Ocean and Southern Ocean, whereas any downward trends in SSA emissions were localized. The DMS fluxes during the study period showed a clear downward trend over most oceans, except for the strong upward trend at low latitudes. In general, the AOD from the MODerate resolution Imaging SpectroRadiometer (MODIS) showed upward trends across the entire Southern Hemisphere (SH), whereas there were downward trends in most areas of the Northern Hemisphere (NH). Therefore, the upward trend of AOD in the SH were derived mainly from the SSA emission trend, due to smaller contribution of anthropogenic sources in the SH.