A 12-year observation of chemical and hygroscopic properties of marine aerosols over the western North Pacific

Abstract:

Anthropogenic emissions from East Asia, especially in China, have significantly increased over the recent decades due to the rapid industrial development. They are implausible to decline in the next 20 years and may have a strong impact on tropospheric chemistry in marine boundary layer and cloud properties over the western North Pacific. To better understand the long-term observation of aerosol characterization and their effect on the hygroscopicity and precipitation process over the western North Pacific, we collected TSP aerosol samples on a weekly basis during the 2001-2012 at a remote marine island, Chichijima (27°04'E; 142°13'N), which is located in the outflow region of Asian dust and East Asian anthropogenic pollutants. We present here long-term observations of seasonal and annual variation of chemical and hygroscopic properties of water-soluble matter, extracted from the remote marine aerosols, based on the measurement of major inorganic ions, total organic carbon and hygroscopicity by HTDMA. Concentrations of nss-SO₄^2- are high in winter and spring and low in summer, whereas hygroscopicity is high in summer to autumn and low in winter to spring, probably due to the influence of long-range transport of anthropogenic pollutants and dusts. Annual variation of nss-SO₄^2- increased from 2001 to 2006 and continuously decreased from 2007 to 2012, probably due to the decreased SO₂ emissions in East Asia especially in China. In contrast, hygroscopicity (g(90%)_ZSR) showed a decrease from 2001 to 2006 and an increase from 2007 to 2012. These results demonstrate that although WSOM often suppress the hygroscopicity of marine aerosols, long-range atmospheric transport of nss-SO₄^2- seriously suppress the hygroscopicity and thus affect the precipitation process over the western North Pacific. This study also demonstrates that Asian dusts can act as an important source of nutrients for phytoplankton and thus sea-to-air emission of dimethyl sulfide and subsequent formation of methanesulfonate and sulfate over the western North Pacific.