Impacts of historical climate and land cover changes on tropospheric ozone and particulate matter in East Asia

Abstract:

To examine the effects associated with changes in climate, land cover, land use, and anthropogenic emissions on surface ozone and particulate matter (PM2.5) between the 5-year periods 1981-1985 and 2007-2011 in East Asia, we perform a series of simulations using a global chemical transport model (GEOS-Chem) driven by assimilated meteorological data and a suite of land cover and land use data. Our results indicate that land cover change alone could lead to a decrease in summertime surface ozone by up to 4 ppbv in East Asia, driven mostly by enhanced dry deposition resulting from climate- and CO2-induced increase in vegetation density, which more than offsets the effect of reduced isoprene emission arising from cropland expansion. Climate change alone could lead to an increase in summertime ozone by 2-10 ppbv in most regions of East Asia, mostly attributable to warming. The combined impacts show that while the effect of climate change on ozone is more pronounced, land cover change could offset part of the climate effect. As results of climate and land cover and land use change, concentrations of sulfate, nitrate, ammonoium, organic carbon and black carbon are simulated to change by -6 to +4 μg m-3, and PM2.5 levels are estimated to change by -12 to +8 μg m-3 in East Asia. The impact of land cover and land use alone on PM air quality is relatively minor (-1 to +1 μg m-3), while the sensitivity of secondary organic aerosol concentation to land cover change are quite significant (-0.5 to +1.5 μg m-3) in comparison with the impact of climate change alone. The changes in anthropogenic emissions remain the largest contributor to deteriorating ozone and PM air quality in East Asia during the study period, but the climate change and land cover changes could lead to a substantial modification of ozone and PM levels.