Chemical analysis of cloud water collected over Hawaii

A limited cloud water sampling program over Hawaii was conducted to provide data on the long-range transport of air-pollutants. Two types of airborne cloud water collectors were developed; one is effective for collecting rainwater (liquid water content (LWC) or = 0.3 g/cu m) and the other, which is nitrogen cooled, is effective for collecting nonprecipitating cloud water (LWC in the range of 0.1 to 1.0 g/cu m). The chemical analysis of cloud water showed that Na/sup +/, Cl/sup -/, and SO/sub 4//sup 2 -/ ion concentrations were approximately 0.0001 m; NH/sub 4//sup +/, NO/sub 3//sup -/, and Ca/sup 2 +/ were one order of magnitude lower. Comparison between cloud water data and seawater chemistry indicates that cloud water has higher molar ratios of SO/sup 2//sub 4//sup -//Cl/sup -/ or SO/sub 4//sup 2 -//Na/sup +/ than seawater by more than one order of magnitude. The pH values were in the range of 4 to 5 regardless of sampling location relative to Hilo City; local anthropogenic sources did not contribute the acidity in this case. The high acidity of cloud water over Hawaii may originate in the ocean from precursors such as H/sup 2/S, COs, CS/sup 2/, or organic sulfur compounds ormore » from long-range transport of anthropogenic pollution, in addition to local pollution, if present. 13 references, 5 figures, 1 table.« less