Features and sources of aerosol properties over the western Pacific Ocean based on shipborne measurements

Abstract

In the Western Pacific, the limited in situ observations of aerosol optical depth (AOD) show substantial north–south differences in its spectral distribution, magnitude, seasonal fluctuation, and Angstrom exponent. Two sets of observation data collected in spring 2017 and summer 2019 are used to investigate aerosol size distribution and its sources through the GRASP (Generalized Retrieval of Aerosol and Surface Properties) inversion method and HYSPLIT (HYbrid Single-Particle Lagrange Integrated Trajectory) particle trajectories model. The retrieved aerosol size distribution (normalized by aerosol volume concentration) is homogeneous over the western Pacific Ocean. The aerosol volume concentration (Cv,c) in the coarse mode is substantially higher than that in the fine mode (Cv,f) in this region, indicating that coarse particles predominate. The northernmost section has the highest Cv,f with an average value of 0.04, which is 4.5 times that of the other sections except the sites observed in 2019, because of the Long-Range Transport (LRT) of dust from the Gobi and Mongolian Plateau. The equatorial section has the highest Cv,c with an average value of 0.22 for the coarse mode, which is 1.5 ~ 3 times higher than that of the other section. Its single scattering albedo (SSA) is the smallest in all sections (SSA(440) = 0.95). Analysis displays that the section is affected by elevated-smoke and polluted-continental/smoke types due to the biomass burning around Papua New Guinea. In addition, an AOD(500) with a value of 0.048, which is lower than the traditional oceanic AOD baseline, is obtained in summer 2019. In comparison to it, the projected net shortwave and longwave radiative effect of spring observed LRT high concentration PM10 plume (AOD(550) = 0.09) from Southeast Asia at the sea surface are − 3.1 W m−2 and − 1.4 W m−2 under clear sky conditions, resulting in a net radiative effect of − 1.7 W m−2. As the cold surge frequency increases due to the warming Arctic, more LRT events may be expected as a result of climate change.