Author(s)

K.-M. Wai & P.A. Tanner

Abstract

This study concerns the long-term variation of the compositions of wet and dry deposition in an Asian megacity. Weekly sampling of wet and dry deposition, from 1988 to 1998, was performed by the Environmental Protection Department of Hong Kong, at two urban monitoring stations Kwun Tong (KT) and Central/Western (CW). We have statistically analysed the accumulated datasets for the soluble and insoluble components. It was found that Na+, Cl-, SO42- were the most abundant components in wet deposition but insoluble Si and soluble calcium were among the most abundant in dry deposition. The volume-weighted mean pH for wet deposition at KT (CW) was 4.46 (4.43), indicating an acid rain scenario in Hong Kong. By contrast, dry deposition was generally basic, with Ca2+ being the most abundant soluble ion. From the weekly sampling program, [Cl-]/[Na+] and [Mg2+]/[Na+] ratios were close to those of seawater for both wet and dry deposition. Least squares linear regression revealed decreases in dry deposition fluxes with time for most components. The sources of components in wet and dry deposition have been discussed. 1 Introduction The composition of wet deposition has been studied extensively in Europe and North America, but in Asia fewer studies have been undertaken. Wang and Wang [l] commented that although northern China accounts for only 9% of the national land area, it accounts for 40% of the national SO2 emissions. Alkaline atmospheric particulate matter exhibits a strong buffering action so that acid rain is not prevalent in northern China. The particulate matter and soil characteristics differ considerably in southern China. Zhao et. al. [2] found, in 1988, that the

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