The role of climate and emission changes in future air quality over southern Canada and northern Mexico

Abstract. Potential impacts of global climate and emissions changes on regional air quality over southern (western and eastern) Canada and northern Mexico are examined by comparing future summers' (i.e., 2049–2051) average regional O₃ and PM_2.5 concentrations with historic concentrations (i.e., 2000–2002 summers). Air quality modeling was conducted using CMAQ and meteorology downscaled from the GISS-GCM using MM5. Emissions for North America are found using US EPA, Mexican and Canadian inventories and projected emissions following CAIR and IPCC A1B emissions scenario. Higher temperatures for all sub-regions and regional changes in mixing height, insolation and precipitation are forecast in the 2049-2051 period. Future emissions are calculated to be lower over both Canadian sub-regions, but higher over northern Mexico. Global climate change, alone, is predicted to affect PM_2.5 concentrations more than O₃ for the projections used in this study: average daily maximum eight (8) hour O₃ (M8hO₃) concentrations are estimated to be slightly different in all examined sub-regions while average PM_2.5 concentrations are estimated to be higher over both Canadian sub-regions (8% over western and 3% over eastern) but 11% lower over northern Mexico. More days are forecast where M8hO₃ concentrations are over 75 ppb in all examined sub-regions but the number of days where PM_2.5 concentration will be over 15 μg/m³ is projected higher only over western Canada. Climate change combined with the projected emissions lead to greater change in pollutant concentrations: average M8hO₃ concentrations are simulated to be 6% lower over western Canada and 8% lower over eastern Canada while average PM_2.5 concentrations are simulated to be 5% lower over western Canada and 11% lower over eastern Canada. Although future emissions over northern Mexico are projected higher, pollutant concentrations are simulated to be lower due to US emissions reductions. Global climate change combined with the projected emissions will decrease average M8hO₃ 4% and PM_2.5 17% over northern Mexico. Significant reductions in the number of days where M8hO₃ concentrations are over 75 ppb and PM_2.5 concentration over 15 μg/m³ are also projected with a significant reduction in peak values.