Global change and regional air quality: Impacts of climate, land-use, and emissions changes

This dissertation examines the impact that projected future (2050's) global changes have on regional air quality in the U.S. (i.e., ozone and PM2.5 concentrations), where the future climate and emissions are based on the Intergovernmental Panel on Climate Change (IPCC) A2 scenario. Specifically, we examine the impact of changes in climate, anthropogenic emissions, chemical boundary conditions, land-use (i.e., biogenic emissions), and the episodic long-range transport (LRT) of Asian emissions. The impact of global changes in climate and emissions, as well as the LRT of Asian emissions, were simulated using the Parallel Climate Model (PCM) and the MOZART-2 global chemical transport model. The PCM and MOZART-2 model results were downscaled to the regional scale using the MM5 meteorological model and the EPA Community Multi-scale Air Quality (CMAQ) photochemical grid model. U.S. anthropogenic emissions were projected to the future using the EPA EGAS economic growth model, while the biogenic emissions were projected using the MEGAN model with adjusted land-use from the Community Land Model.;Model results show that changes in chemical boundary conditions have the most significant impact on summertime U.S. ozone concentrations (+5 ppbv), followed by changes in anthropogenic emissions (+3 ppbv), and climate changes (-1.3 ppbv). Changes in July PM2.5 concentrations are primarily influenced by changes in anthropogenic emissions (+3 mug m-3), while changes in chemical boundary conditions have a minimal impact and only increase PM2.5 concentrations by +0.4 mug m-3. On average, climate change tends to reduce PM2.5 concentrations by roughly -0.9 mug m-3, with the largest decreases occurring in the south eastern U.S. (-3 mug m-3) due to increased wet deposition. The episodic LRT of Asian emissions to the western U.S. is found to elevate surface ozone concentrations in the Pacific Northwest 1-2 ppbv above the average (∼48 ppbv) during present-day events, and 1-3 ppbv above the average (∼58 ppbv) in the future. In California, surface ozone increases slightly during wintertime LRT events in both the present-day and future cases, but ozone decrease during summertime events due to the meteorological conditions associated with LRT events.