Attribution of projected changes in summertime US ozone and PM2.5 concentrations to global changes

摘要

The impact that changes in future climate, anthropogenic US emissions,background tropospheric composition, and land-use have on summertimeregional US ozone and PM concentrations is examined through a matrixof downscaled regional air quality simulations, where each set ofsimulations was conducted for five months of July climatology, using theCommunity Multi-scale Air Quality (CMAQ) model. Projected regional scalechanges in meteorology due to climate change under the IntergovernmentalPanel on Climate Change (IPCC) A2 scenario are derived through thedownscaling of Parallel Climate Model (PCM) output with the MM5meteorological model. Future chemical boundary conditions are obtainedthrough downscaling of MOZART-2 (Model for Ozone and Related ChemicalTracers, version 2.4) global chemical model simulations based on the IPCCSpecial Report on Emissions Scenarios (SRES) A2 emissions scenario.Projected changes in US anthropogenic emissions are estimated using the EPAEconomic Growth Analysis System (EGAS), and changes in land-use areprojected using data from the Community Land Model (CLM) and the SpatiallyExplicit Regional Growth Model (SERGOM). For July conditions, changes inchemical boundary conditions are found to have the largest impact (+5 ppbv)on average daily maximum 8-h (DM8H) ozone. Changes in US anthropogenicemissions are projected to increase average DM8H ozone by +3 ppbv. Land-usechanges are projected to have a significant influence on regional airquality due to the impact these changes have on biogenic hydrocarbonemissions. When climate changes and land-use changes are consideredsimultaneously, the average DM8H ozone decreases due to a reduction inbiogenic VOC emissions (−2.6 ppbv). Changes in average 24-h (A24-h)PM concentrations are dominated by projected changes inanthropogenic emissions (+3 μg m), while changes in chemicalboundary conditions have a negligible effect. On average, climate changereduces A24-h PM concentrations by −0.9 μg m, but thisreduction is more than tripled in the Southeastern US due to increasedprecipitation and wet deposition.