Abstract
Abstract. To understand more fully the effects of global changes on ambient concentrations of ozone and particulate matter with aerodynamic diameter smaller than 2.5 μm (PM2.5) in the United States (US), we conducted a comprehensive modeling effort to evaluate explicitly the effects of changes in climate, biogenic emissions, land use and global/regional anthropogenic emissions on ozone and PM2.5 concentrations and composition. Results from the ECHAM5 global climate model driven with the A1B emission scenario from the Intergovernmental Panel on Climate Change (IPCC) were downscaled using the Weather Research and Forecasting (WRF) model to provide regional meteorological fields. We developed air quality simulations using the Community Multiscale Air Quality Model (CMAQ) chemical transport model for two nested domains with 220 and 36 km horizontal grid cell resolution for a semi-hemispheric domain and a continental United States (US) domain, respectively. The semi-hemispheric domain was used to evaluate the impact of projected global emissions changes on US air quality. WRF meteorological fields were used to calculate current (2000s) and future (2050s) biogenic emissions using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). For the semi-hemispheric domain CMAQ simulations, present-day global emissions inventories were used and projected to the 2050s based on the IPCC A1B scenario. Regional anthropogenic emissions were obtained from the US Environmental Protection Agency National Emission Inventory 2002 (EPA NEI2002) and projected to the future using the MARKet ALlocation (MARKAL) energy system model assuming a business as usual scenario that extends current decade emission regulations through 2050. Our results suggest that daily maximum 8 h average ozone (DM8O) concentrations will increase in a range between 2 to 12 parts per billion (ppb) across most of the continental US. The highest increase occurs in the South, Central and Midwest regions of the US due to increases in temperature, enhanced biogenic emissions and changes in land use. The model predicts an average increase of 1–6 ppb in DM8O due to projected increase in global emissions of ozone precursors. The effects of these factors are only partially offset by reductions in DM8O associated with decreasing US anthropogenic emissions. Increases in PM2.5 levels between 4 and 10 μg m−3 in the Northeast, Southeast, Midwest and South regions are mostly a result of increase in primary anthropogenic particulate matter (PM), enhanced biogenic emissions and land use changes. Changes in boundary conditions shift the composition but do not alter overall simulated PM2.5 mass concentrations.
Highlights
Despite extensive efforts to reduce anthropogenic emissions, air pollution continues to be a public health issue in the United States (US EPA, 2010)
We have investigated the individual and combined contributions of factors that impact US air quality by dynamically downscaling future climate projections using the Weather Research and Forecasting (WRF) model and using the regional chemical transport model Community Multiscale Air Quality Model (CMAQ) version 4.7.1
That positive influence is offset by (1) increasing global emissions and changes in long-range transport, which have a negative impact on air quality across the domain; (2) climate changes, which increase ozone concentrations in the Central, South, Midwest, Northeast and Southeast regions of the domain; and (3) increases in US biogenic volatile organic compounds (BVOCs) emissions, which increase ozone concentrations in regions with high biogenic emissions such as the South, Midwest, Northeast and Southeast
Summary
Despite extensive efforts to reduce anthropogenic emissions, air pollution continues to be a public health issue in the United States (US EPA, 2010). We present a continuation of the work described by Avise et al (2009) and Chen et al (2009a, b), who downscaled the Parallel Climate Model (PCM; Washington et al, 2000) and MOZART (Model for OZone And Related chemical Tracers; Horowitz, 2006) global model output for the A2 IPCC scenario using MM5 and the Community Multiscale Air Quality Model (CMAQ; Byun and Schere, 2006) to simulate current and future air quality in the US For this update, we implemented a semi-hemispheric domain for the Weather Research and Forecasting (WRF) mesoscale meteorological model (http://www.wrf-model.org) and CMAQ simulations in lieu of using MOZART output for chemical boundary conditions for our CONUS CMAQ simulations.
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