The Co-Benefits of Global and Regional Greenhouse Gas Mitigation on US Air Quality at Fine Resolution

Thursday, 18 December 2014
Yuqiang Zhang1, Jared Heath Bowden1, Zachariah Adelman1,2, Vaishali Naik3, Larry Wayne Horowitz4, Steven Smith5 and James J West6, (1)University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, (2)Institute for the Environment, Chapel Hill, NC, United States, (3)UCAR/GFDL, Princeton, NJ, United States, (4)Princeton Univ, Princeton, NJ, United States, (5)Joint Global Change Research Institute, College Park, MD, United States, (6)Univ. of North Carolina, Chapel Hill, NC, United States
Reducing greenhouse gases (GHGs) not only slows climate change, but can also have co-benefits for improved air quality. In this study, we examine the co-benefits of global and regional GHG mitigation on US air quality at fine resolution through dynamical downscaling, using the latest Community Multi-scale Air Quality (CMAQ) model. We will investigate the co-benefits on US air quality due to domestic GHG mitigation alone, and due to mitigation outside of the US. We also quantity the co-benefits resulting from reductions in co-emitted air pollutants versus slowing climate change and its effects on air quality. Projected climate in the 2050s from the IPCC RCP4.5 and RCP8.5 scenarios is dynamically downscaled with the Weather Research and Forecasting model (WRF). Anthropogenic emissions projections from the RCP4.5 scenario and its reference (REF), are directly processed in SMOKE to provide temporally- and spatially-resolved CMAQ emission input files. Chemical boundary conditions (BCs) are obtained from West et al. (2013), who studied the co-benefits of global GHG reductions on global air quality and human health.

Our preliminary results show that the global GHG reduction (RCP4.5 relative to REF) reduces the 1hr daily maximum ozone by 3.3 ppbv annually over entire US, as high as 6 ppbv in September. The west coast of California and the Northeast US are the regions that benefit most. By comparing different scenarios, we find that foreign countries’ GHGs mitigation has a larger influence on the US ozone decreases (accounting for 77% of the total decrease), compared with 23% from domestic GHG mitigation only, highlighting the importance of methane reductions and the intercontinental transport of air pollutants. The reduction of global co-emitted air pollutants has a more pronounced effect on ozone decreasing, relative to the effect from slowing climate and its effects on air quality. We also plan to report co-benefits for PM2.5 in the US.