ABSTRACT
Biomass burning in Southeast Asia had become a significant concern to the general public as well as governments in the region. The aerosols emitted from biomass burning can cause persistent low-visibility or haze events under certain weather conditions in downwind locations and cause human health issues. Also, fire aerosols affect cloud and precipitation phenomena. In this study, we used surface visibility data for estimating haze frequency in the major cities of Southeast Asia. Furthermore, we also conducted numerical model simulations with different aerosol emission scenarios: fossil fuel emissions only, biomass burning emissions only, or the combination of fossil fuel and biomass burning emissions to identify the contribution of fire-aerosol-caused low visibility days (visibility <10 km). We found that biomass burning aerosols account for ~90% of severe haze events (visibility <7 km) in the major cities of Southeast Asia, whereas, more often unhealthy conditions build from a combination of fossil fuel burning and biomass burning aerosols. Besides air quality, convective systems in the Maritime Continent are also significantly influenced by the massive biomass burning aerosols during the transit period of Southeast Asian monsoons. Specifically, under the influence of biomass burning aerosols, rainfall in Borneo associated with westerly low-level wind pattern induced by active anticyclonic circulation over the northwest Borneo tends to become less intensive during the midnight or early morning.
