The impact of the 1997–1998 El Niño event on the tropospheric ozone distribution and related processes is assessed by a simulation using a global chemical model. The changes in tropospheric ozone observed during the 1997–1998 El Niño are considered to have been caused by large-scale processes due to the shift in the tropical convection pattern associated with sea surface temperature (SST) changes and by large emissions of ozone precursors due to pronounced biomass burning in the Indonesian region (mainly in Sumatra and Borneo). This simulation study is focused on the effects of meteorological changes caused by the El Niño, aside from the effects of the Indonesian biomass burning. Our simulation results show that about half of the ozone increase observed over the equatorial western Pacific and Indonesia (6–12 Dobson units in tropospheric column ozone) can be explained by the meteorological effects of the El Niño with the remainder attributed to the Indonesian biomass burning, whereas the ozone decrease over the eastern Pacific (4–8 Dobson units) can be attributed to the meteorological effects alone. Moreover, our study suggests that a change in photochemical processes (e.g., water vapor concentration controlling the lifetimes of ozone and other related species, and wet scavenging associated with convective precipitation) also plays an important role in the tropical ozone distribution during the course of the 1997–1998 El Niño event.
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