Aircraft measurements of ozone, NOx, CO, and aerosol concentrations in biomass burning smoke over Indonesia and Australia in October 1997: Depleted ozone layer at low altitude over Indonesia

The 1997 El Nino unfolded as one of the most sever El Nino Southern Oscilla tion (ENSO) events in this century and it coincided with massive biomass bu rning in the equatorial western Pacific region. To assess the influence on the atmosphere, aircraft observations of trace gases and aerosol were condu cted over Kalimantan in Indonesia and Australia. Over Kalimantan in Indones ia, high concentrations of O-3, NOx, CO, and aerosols were observed during the flight. Although the aerosol and NOx decreased with altitude; the O-3 h ad the maximum concentration (80.5 ppbv) in the middle layer of the smoke h aze and recorded very low concentrations (similar to 20 ppbv) in the lower smoke layer. This feature was Dot observed in the Australian smoke. We prop osed several hypotheses for the low O-3 concentration at low levels over Ka limantan. The most likely are lack of solar radiation and losses at the sur face of aerosol particles.