Impact of Seasonal Biomass Burning on Air Quality in the 'Top End' of Regional Northern Australia

Abstract

This study examines the impact of biomass burning on the air environment of the Top End of the Northern Territory, Australia. Northern Australia, a savanna region, has a tropical monsoonal climate with clearly defined wet and dry seasons. Extensive biomass burning occurs in this region throughout the dry season. Ninety-seven stacked filter unit (SFU) samples were collected at Jabiru East in northern Australia between May 1995 and December 1996. The SFU sampler separates the collected particulate matter into a coarse fraction, 2-10 m equivalent aerodynamic diameter (EAD) and a fine fraction, <2 m EAD. These samples were analysed for particulate mass (PM) by gravimetric methods and black carbon (BC) by a reflectance technique. The median coarse and fine particulate mass levels were 5.7 ng/m3 and 4.7 g/m3 respectively with median coarse and fine black carbon levels at 97 ng/m3 and 570 ng/m3 respectively. Fine range PM and BC were highly correlated (R=0.92) but there was only a moderate correlation between coarse range PM and BC (R=0.80). Strong seasonal dependencies were observed for coarse and fine PM and for fine BC at Jabiru East. These findings are attributed to the seasonal nature of both sources and removal processes, e.g. one of the dominant sources in the region is biomass burning, and wet deposition is an important removal process. Also seasonal factors such as wind speed, soil moisture and vegetation cover, all influence the level of physically generated particles.