Aerosol light-scattering coefficient at 530 nm and its hygroscopic growth were determined in biomass-burning smoke in the lower atmosphere over Kalimantan and northern Australia during the 1997 dry-season fires. Both in and away from plumes, light-scattering was considerably greater in the Indonesian region and hygroscopic growth in scattering was also consistently greater. The relative increase in scattering, from 20% to 80% relative humidity, was typically 1.37 in northern Australian and 1.65 in Kalimantan. Limited aerosol light absorption data indicate relatively small absorption in the Indonesian smoke. In part these differences can be explained by different combustion phases, mixed flaming and smoldering in the Australian savanna fires compared with predominantly smoldering in Indonesia, although these and other concurrent measurements suggest that underground peat combustion may have made a significant contribution to the Indonesian smoke. ¿ 1999 American Geophysical Union