Long-term observations of regional aerosol composition at two sites in Indonesia

Abstract

Aerosol samples were collected with Gent PM10 stacked filter unit (SFU) samplers at Bukit Tinggi, a mountain site on Sumatra, and at Pontianak, a sea-level site on Kalimantan. The Gent PM10 SFU sampler provides two size fractions: coarse (2–10 μm equivalent aerodynamic diameter (EAD)) and fine (<2 μm EAD). At Bukit Tinggi, 130 SFU samples were taken from April 1996 to August 1999, and at Pontianak, 66 samples from the end of December 1997 to June 1999. All samples were analysed for the particulate mass (PM), black carbon (BC), and up to 47 elements. A combination of particle-induced X-ray emission spectrometry and instrumental neutron activation analysis was used for the multielemental analyses. The average fine-to-coarse ratios were at both sites around 1 for the PM, but above 2 (up to 5) for BC, S, Sb, I and Pb. The median PM concentrations (and interquartile ranges) in the coarse size fraction were 4.8 (3.8–5.6) and 12 (9–14) μg/m 3 at Bukit Tinggi and Pontianak, respectively. For the fine fraction, the corresponding numbers were 4.5 (2.6–9.1) and 9.4 (6.5–13) μg/m 3. Principal component analysis was applied to the fine fraction data sets in order to identify the contributing sources (source types). At Bukit Tinggi, five components were identified, i.e., a crustal component, a biomass burning component (with loadings of 0.7–0.9 for BC, K, Br, Rb and I), an oil combustion component (with S and V), a pollution component (with Sb and Pb), and a Na component.