A sensitivity simulation of tropospheric ozone changes due to the 1997 Indonesian fire emissions

A global chemical transport model, called MOZART, is used to investigate th e photochemical impact of the 1997 Indonesian fires on tropospheric ozone a nd its precursors in the tropics. Due to the high release of carbon monoxid e by peat fires, CO increases by up to 1000 ppbv in the free troposphere ov er Indonesia. As a consequence of increased photochemical production, ozone is significantly perturbed over source regions (Sumatra and Kalimantan). T he tropospheric O-3 column increases by 20-25 DU and the ozone mixing ratio reaches 50 ppbv in the mid-troposphere in November. South of the source re gion, low ozone mixing ratios of 20-25 ppbv are calculated in the boundary layer due to marine air influence and reduced photochemical activity in pre sence of biomass burning aerosols. The particular transport regime prevaili ng during the 1997 El Nino event is not considered in our calculations. Thi s limitation precludes any definitive conclusion regarding the relative rol e played by photochemistry and transport processes on the distribution of s pecies during the 1997 fires.