Concentrations of nitrogen and sulfur species in gas and rainwater from six sites in Indonesia

Abstract

Gas mixing ratios of SO2, NO2 and HNO3 and nitrate and sulfate concentrations in rainwater have been measured at six sites in Indonesia. The sites, Jakarta, Serang, Cilegon, Merak and Bogor, in Java, and Bukit Koto Tabang in Sumatra, provide a range of pollution regimes in Indonesia. Jakarta and Bogor are heavily polluted sites in Java, whereas Bukit Koto Tabang is a clean air station in a relatively unpopulated area on the west coast of equatorial Sumatra. At these sites rainwater was collected daily and gas samples weekly during 1996. The other three sites Serang, Cilegon and Merak represent smaller regional towns in west Java. At these sites rainwater samples were collected weekly from June 1991 until June 1992. The results show that Jakarta has the highest volume-weighted mean sulfate concentrations in rainwater while the lowest were measured at Bukit Koto Tabang. Volume-weighted mean nitrate concentration was about 24 μeq L-1 at Jakarta and Bogor, significantly higher than the 0.8 μeq L-1 measured at Bukit Koto Tabang. Sulfur dioxide mixing ratios ranged from 4-7 ppbv in Jakarta to an average of 1.3 ppbv at Bukit Koto Tabang. Nitrogen dioxide mixing ratio was highest in Jakarta averaging 28 ppbv compared with the background mixing ratio of 1.2 ppbv at Bukit Koto Tabang. Using dry deposition velocities estimated during a separate study in the similar conditions of Malaysia enabled dry deposition estimates of SO2, HNO3 and NO2. Results of estimated total acidic S and N deposition (wet and dry) were greater than 250 meq m-2 yr-1 at the Jakarta and Bogor sites compared with about 23 meq m-2 yr-1 at Bukit Koto Tabang. At Jakarta and Bogor dry deposition accounted for more than 50% of the total deposition estimates compared with about 20% at Bukit Koto Tabang. Such deposition rates are high when compared to critical loads estimated for Indonesia by the RAINS-Asia model. In this model, critical loads in western Java and equatorial western Sumatra fall into one of two classes: 50-100 and 20-50 meq m-2 yr-1. Thus acidic deposition flux at Jakarta and Bogor was found to be above the predicted critical loads even for the more acid insensitive soils.