Seasonal characteristics of emission, distribution, and radiative effect of marine organic aerosols over the western Pacific Ocean: an investigation with a coupled regional climate-aerosol model.

Organic aerosols from marine sources over the western Pacific Ocean of East Asia were investigated by using an online-coupled regional chemistry-climate model RIEMS-Chem for the entire year 2014. Model evaluation against a wide variety of observations from research cruises and in-situ measurements demonstrated a good skill of the model in simulating temporal variation and spatial distribution of particulate matter with aerodynamic diameter less than 2.5 μm and 10 μm (PM_2.5 and PM₁₀), black carbon (BC), organic carbon (OC), sodium, and aerosol optical depth (AOD) in the marine atmosphere. The inclusion of marine organic aerosols apparently improved model performance on OC aerosol concentration. The regional and annual mean near surface marine organic aerosol (MOA) concentration was estimated to be 0.27 μg m^-3, with the maximum in spring and the minimum in winter and contributed 26% of the total organic aerosol concentration on average over the western Pacific. Marine primary organic aerosol (MPOA) accounted for the majority of marine organic aerosol (MOA) mass and exhibited the maximum in autumn and the minimum in summer, whereas marine secondary organic aerosol (MSOA) was approximately 1~2 orders of magnitude lower than MPOA, having a distinct summer maximum and a winter minimum. MOA induced a direct radiative effect (DRE_MOA) of -0.27 W m^-2, and an indirect radiative effect (IRE_MOA) of -0.66 W m^-2 at TOA (IRE_MOA) in terms of annual and oceanic average over the western Pacific, with the highest seasonal mean IRE_MOA up to -0.94 W m^-2 in spring. IREMOA was stronger than but in a similar magnitude to the IRE due to sea salt aerosol on average, and it was approximately 9% of the IRE due anthropogenic aerosols in terms of annual mean over the western Pacific, and this ratio increased to 19% in the northern parts of the western Pacific in autumn. This study reveals an important role of MOA in perturbing cloud properties and shortwave radiation fluxes in the western Pacific of East Asia. [ABSTRACT FROM AUTHOR]