Very high weight ratios of S/K in individual haze particles over Kalimantan during the 1997 Indonesian forest fires

The elemental composition of individual aerosol particles of 0.15–3 μm radius, collected over Kalimantan during the 1997 Indonesian forest fire event, was analyzed using a transmission electron microscope equipped with an energy-dispersive X-ray analyzer (EDX). Although 60–90% of the particles collected at altitudes of 1–5 km contained K, they exhibited high weight ratios of S/K with median values of 9–18 independent of particle size. These were much larger than those (median values of 2–4) obtained from the forest fires in northern Australia. The high weight ratios over Kalimantan are considered to be due to the heterogeneous growth of particles through the oxidation of SO2. In addition to SO2 from the combustion of forest biomass, SO2 originating from the combustion of peat below the ground is believed to have been important in producing the high S/K ratios.