APPLICATION OF ION CHROMATOGRAPHY TO THE HONG-KONG RAINFALL MONITORING PROGRAM

Results from a rainwater monitoring program in Hong Kong from May 1994 to April 1995, with 60 sample collection days, are presented for Cl-, NO3- and SO42- concentrations from suppressed and non-suppressed colu mn ion chromatography. Replicate sampling was employed on a daily basi s using both bulk (B) and wet only (W) samplers, and there was no stat istically significant difference between the B-W datasets for Cl-, NO3 - and SO42- concentrations in rainwater. From the more complete bulk s ample collection dataset (n=60), large changes in analyte concentratio ns were observed for samples collected on different days, with the ran ges (in mu equiv. l(-1)) 3-348 for Cl-, 3-132 for NO3- and 12-303 for SO42-. Neglecting the February 1995 dataset for which n=1, the volume- weighted monthly mean concentrations displayed narrower ranges, being 16-61, 7-42 and 27-87 respectively. The nature of the source of the an alyte and its flux, type of weather system, season and atmospheric con ditions, together with the rainfall amount and intensity are some of t he factors which produce the changes in analyte concentrations. Below- cloud washout processes cause large changes in analyte concentration a t the start of a single rain event, and contribute to the horizontal l ocal variation in analyte concentrations. The ratio of SO42--NO3- in H ong Kong rainwater has decreased since 1992 and the reasons for this a re discussed.