The effects of smoke and dust aerosols on UV-B radiation in Australia from ground-based and satellite measurements

Abstract

An understanding of the effect of aerosols on biologically- and photochemically-active UV radiation reaching the Earth's surface is important for many ongoing climate, biophysical, and air pollution studies. In particular, estimates of the UV characteristics of the most common Australian aerosols will be valuable inputs to UV Index forecasts, air quality studies, and assessments of the impact of regional environmental changes. Based on MODIS fire maps and MISR aerosol property retrievals, we analyzed the climatological distributions of Australian dust and smoke particles and identified two sites where ground-based UV-B spectra were available during episodes of relatively high aerosol activity. Since mid-2003, surface UV spectra (285-450 nm) have been measured routinely at Darwin and Alice Springs in Australia by the Australian Bureau of Meteorology (BoM). Using collocated AERONET sunphotometer measurements at Darwin and collocated BoM sunphotometer measurements at Darwin and Alice Springs, we identified several episodes of relatively high aerosol activity that could be used to study the effects of dust and smoke on the UV-B solar irradiance at the Earth's surface. To assess smoke effects we compared the measured UV irradiances at Darwin with irradiances simulated with the libRadtran radiative transfer model for aerosol-free conditions. We found that for otherwise similar atmospheric conditions, aerosols reduced the UVB irradiance by 50% near the fire source and up to 15% downwind. We also found the effect of smoke particles to be 5 to 10% larger in the UV-B than in the UV-A. For the selected period at Darwin, changes in the aerosol loading gave larger variations in the surface UV irradiances than previously reported changes seen in the ozone column. We are continuing similar investigations for the Alice Springs site to assess spectral differences between smoke and dust aerosols.