Atmospheric transport and deposition of anthropogenic substances from the Asia to the East China Sea

Abstract

Experiments conducted aboard the R/V Hakuho Maru (Cruise KH-02-3) in the autumn of 2002 were designed to study the pathways of atmospheric aerosol transport, selected trace elements and major ions composition of particles and quantify their dry deposition over the East China Sea. We determined the concentrations of trace elements Al, Mn, Pb, Se, and Zn and major ions Na⁺, SO₄^2- and NO₃^- in aerosol particles. Aerosols were continuously collected in fine and coarse size fractions with a cut off at 2.5 μm. Particle number densities (volumes) were determined in four size ranges between 0.1 and <0.5 μm. High Al concentrations in the coarse mode fractions suggest continental origin of these aerosols. Weather charts revealed conducive meteorological conditions for northeastward air mass transports from the Asian continent. Back trajectory analysis results corroborated with the meteorological observations. Nss-SO₄^2-, Mn, Pb, Se and Zn were more abundant in the fine than coarse mode fraction, but NO₃^- was associated with the latter. About three-fold higher Mn/Al ratio in fine mode than in coarse aerosols (0.042 vs. 0.015, respectively) and a strong correlation between non-crustal Mn and nss-SO₄^2- suggest that fine Mn originates from industrial sources. Similarly, non-crustal Pb and Zn in the fine fraction were again significantly correlated with nss-SO₄^2- indicating major contributions from anthropogenic activities. Our results highlight the fact that atmospheric pollutants from Asia, including heavy metals and major ions, are carried to the East China Sea even during non-dusty periods. It is necessary to obtain the atmospheric deposition fluxes, wet and dry, throughout the year both by periodic and continuous atmospheric measurements in order to find the biogeochemical significance of Asian aerosols to the East China Sea and North Pacific Ocean.