A regional model study of the characteristics and indirect effects of marine primary organic aerosol in springtime over East Asia

An online coupled regional chemistry-aerosol-climate model was developed and applied to explore the distribution, evolution and indirect effects of marine primary organic aerosols (MPOA) over East Asia during the period from 12 March to 22 April 2014. Model results were compared with a variety of observations from ground measurement, cruise experiment and satellite retrievals, which demonstrated the model was capable of reproducing reasonably well the major features in meteorological variables, gas species, aerosol components and cloud properties in the western Pacific Ocean in springtime. Active bloom events were observed in the western Pacific Ocean during the study period, with mean surface seawater Chlorophyll a (Chl-a) concentrations up to 10 mg (-3) in the Yellow Sea, East China Sea, Sea of Japan, as well as the ocean northeast of Japan. The mean surface MPOA concentration was simulated to be up to 2.5 mu g m(-3) in the East China Sea, followed by that in the ocean northeast of Japan, and about 0.5 mu g m(-3) in the coastal areas of east China. MPOA generally caused increases in the cloud condensation nuclei (CCN), cloud droplet number concentration (CDNC), cloud optical depth (COD) and cloud liquid water path (CLWP), but decrease in the cloud droplet effective radius (CDER). The above changes in cloud properties induced a negative indirect radiative effect (IRE), with the mean values being -5.3 Wm(-2), -8.2 Wm(-2) and -12.2 Wm(-2) over the ocean, East China Sea and the north western Pacific Ocean, which accounted for about 40%, 35% and 51% of the IRE due to all aerosols in these regions, respectively. It was noteworthy that the MPOA induced IRE was -3.6 Wm(-2) in east China, accounting for 20% of the IRE by all aerosols and the percentage contribution was about 32% for the whole domain, suggesting its important influence on cloud and radiation during the study period. The sensitivity of MPOA activation to the factors affecting hygroscopicity and surface tension was examined by sensitivity simulations. The indirect effects of MPOA tended to suppress precipitation in most of the domain, with the maximum decrease in the accumulated precipitation up to 50 mm in parts of south China and the East China Sea. In terms of domain average, MPOA accounted for 16%, 22%, 18% of the precipitation reduction due to all aerosols over the land, ocean and the whole domain, respectively, indicating its nonnegligible influence on precipitation over East Asia in springtime 2014.