A comparison between filtered and unfiltered atmospheric depositions from a rural area in Hong Kong

Since early 1994, an atmospheric wet deposition sampling programme has been added to the pre-existing daily and weekly bulk deposition sampling programme at the rural Kadoorie Agricultural Research Centre (K.A.R.C.) in Hong Kong. In this paper, we compare the pH of filtered and unfiltered, bulk and wet daily deposition samples, measured immediately after their collection. The pH measurements were made on nearly 60 sets of samples. It is found that the difference between the pH of filtered and the unfiltered depositions both, wet and bulk is statistically insignificant at the 0.05 level, suggesting a negligible influence on the acid-base reactions of “dry-deposited” material ( 0.4 μm) on the rainwater chemistry at the K.A.R.C. However, this is not valid for the difference between the bulk (unfiltered)-wet (filtered) pair of samples, although the two are strongly correlated (R = 0.961) with a slope ≈ 1.00.