Abstract
Abstract. In order to characterize the long-term trend of remote marine aerosols, a 12-year observation was conducted for water-soluble ions in TSP (total suspended particulate) aerosols collected from 2001 to 2012 in the Asian outflow region at Chichijima Island in the western North Pacific. We found a clear difference in chemical composition between the continentally affected and marine background air masses over the observation site. Asian continental air masses are delivered from late autumn to spring, whereas marine air masses were dominated in summer. Concentrations of non-sea salt (nss-) SO42−, NO3−, NH4+, nss-K+ and nss-Ca2+ are high in winter and spring and low in summer. On the other hand, MSA− (methanesulfonate) exhibits higher concentrations during spring and winter, probably due to springtime dust bloom or due to the direct continental transport of MSA− to the observation site. We could not find any clear decadal trend for Na+, Cl−, Mg2+ and nss-Ca2+ in all seasons, although there exists a clear seasonal trend. However, concentrations of nss-SO42− continuously decreased from 2007 to 2012, probably due to the decreased SO2 emissions in East Asia especially in China. In contrast, nss-K+ and MSA− concentrations continuously increased from 2001 to 2012 during winter and spring seasons, demonstrating that biomass burning and/or terrestrial biological emissions in East Asia are being increasingly transported from the Asian continent to 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 over the western North Pacific.
Highlights
The atmosphere is mostly composed of gases and contains suspended liquid and solid particles called aerosols
In order to assess the quality of the analysis, we performed an ion balance calculation using major anions (Cl−, SO24−, NO−3 ) and cations (Na+, NH+4, K+, Ca2+, and Mg2+) assuming that most of the ions are in the solutions
Water-soluble inorganic ions in the total suspended particulate (TSP) aerosols are dominated by sea salt particles (Na+ and Cl−), which www.atmos-chem-phys.net/15/6437/2015/
Summary
The atmosphere is mostly composed of gases and contains suspended liquid and solid particles called aerosols. Marine aerosols perturb Earth’s radiation balance directly by scattering and absorbing the incoming solar radiation or indirectly by acting as cloud condensation nuclei (CCN) and altering their water uptake properties (Twomey, 1977; Charlson et al, 1991; Ramanathan et al, 2001) The strength of these direct and indirect effects depends on the concentration, size distribution, and chemical composition of the atmospheric aerosols (Coakley et al, 1983). Chichijima Island, a remote marine site in the western North Pacific, is located on the lee side of a large industrial area; this site is well suitable for the study of longrange transport of air pollutants in East Asia and the perturbation of anthropogenic activity in the remote marine atmosphere. Transport of continental aerosols to the remote ocean area, we carried out measurements of atmospheric aerosols at Chichijima Island in the western North Pacific
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