Impacts of Projected Changes of Emissions and Climate on Future U.s. Air Quality

Projected changes in emissions and climate will impact future air quality and related human and environmental health. In this work, an advanced online-coupled meteorology and chemistry model, the Weather Research and Forecasting Model with Chemistry (WRF/Chem), has been applied to the continental U.S. for current (2001–2010) and future (2046–2055) decades under four emission/ climate scenarios including the Representative Concentration Pathways (RCP) 4.5 and 8.5 that regulate future radiative forcing and the Technology-driven model (TDM) A1B and B2 that explicitly simulate the relationship between the socioeconomic variables and technological changes. A comprehensive evaluation has been performed for current decade using available observations from surface networks and satellites and shows an overall good performance in reproducing observations. The future decadal simulations show that future climate features with stronger radiation, higher surface temperature and planetary boundary layer height, and enhanced precipitation under all scenarios, with less warming and drier atmosphere by RCP4.5 than 8.5 and by TDM B2 than A1B. The simulations under RCP8.5/TDM A1B show the enhanced future O3 levels, which are attributed to warmer climate, higher emissions of methane (CH4) and biogenic volatile organic compounds (VOCs), and dis-benefit of nitrogen oxides (NOx) reduction in VOC-limited regime. The latter factor offsets the benefits of reduced emissions of NOx and anthropogenic VOCs. Future air quality features greater reduction in PM2.5 by RCP4.5/8.5 than TDM B2/A1B and decreased O3 over most areas by RCP4.5 and TDM B2, indicating the benefits of carbon policy and technology changes with greater emission reductions and the importance of win–win emission control strategies in mitigating air pollution and adverse climate change.