The potential effects of climate change on air quality across the conterminous US at 2030 under three Representative Concentration Pathways
Nolte, Chris, T. Spero, J. Bowden, M. Mallard, AND P. Dolwick. The potential effects of climate change on air quality across the conterminous US at 2030 under three Representative Concentration Pathways. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 18(20):15471-15489, (2018). https://doi.org/10.5194/acp-18-15471-2018
For states to attain compliance with the National Ambient Air Quality Standards (NAAQS) in future years, it is important to understand the complex set of factors that form air pollution. Pollutants that are partially or entirely formed through atmospheric reactions—PM2.5 and ozone—have been especially challenging for some areas of the country. Meteorology—including temperature, humidity, and precipitation—can significantly alter pollutant formation and loss from the environment. Climate change is anticipated to cause significant variations in meteorology over the United States. To support environmental decision making by states, there is an Agency need to understand changes in meteorological patterns and resulting impacts on air quality. States containing areas with air pollution concentrations exceeding the NAAQS are required to develop State Implementation Plans (SIPs) that will bring those areas into attainment. EPA (through OAR/OAQPS) may need to consider whether to require states to take climate change into account in SIP development, and what guidance to provide as to the most appropriate method for doing so. This paper provides a demonstration of a linked system of global to regional models for simulating future air quality, as well as results obtained using such a modeling system for a policy-relevant time frame.
The potential impacts of climate change on regional ozone (O3) and fine particulate (PM2.5) air quality in the United States are investigated by downscaling Community Earth System Model (CESM) global climate simulations with the Weather Research and Forecasting (WRF) model, then using the downscaled meteorological fields with the Community Multiscale Air Quality (CMAQ) model. Regional climate and air quality change between 2000 and 2030 under three Representative Concentration Pathways (RCPs) is simulated using 11-year time slices from CESM. The regional climate fields represent historical daily maximum and daily minimum temperatures well, with mean biases less than 2 K for most regions of the U.S. and most seasons of the year and good representation of diurnal variability. Precipitation in the central and eastern U.S. is well simulated for the historical period, with seasonal and annual biases generally less than 25%, and positive biases in the western U.S. throughout the year and in part of the eastern U.S. during summer. Maximum daily 8-h ozone is projected to increase during summer and autumn in the central and eastern U.S. The increase in summer O3 is largest under RCP8.5, exceeding 4 ppb, with smaller increases of up to 2 ppb simulated during autumn and changes during spring generally less than 1 ppb. Increases are magnified at the upper end of the O3 distribution, particularly where projected increases in temperature are greater. Annual average PM2.5 concentration changes by up to ± 1 ug/m3. Organic matter concentration increases occur during summer and autumn due to increased biogenic emissions. Decreases in aerosol nitrate occur during winter, accompanied by lesser decreases in ammonium and sulfate, due to warmer temperatures causing increased partitioning to the gas phase. Among meteorological factors examined to account for modeled changes in pollution, temperature and isoprene emissions are found to have the largest changes and the greatest impact on O3 concentrations.