The effects of global change upon United States air quality

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 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 Asian 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 ppb across most of the continental US, with the highest increase in the South, Central, and Midwest regions of the US, due to increases in temperature, enhanced biogenic emissions, and changes in land use. 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 2 and 4 μg m−3 in the Northeast, Southeast, and South regions are mostly a result of enhanced biogenic emissions and land use changes. Little change in PM2.5 in the Central, Northwest, and Southwest regions was found, even when PM precursors are reduced with regulatory curtailment. Changes in temperature, relative humidity, and boundary conditions shift the composition but do not alter overall PM2.5 mass concentrations.

Air Quality and Climate Connections

“…Many studies neglect potentially important climate-induced changes in emissions from natural sources, such as increasing wildfires in the western U.S. Simulated climate warming leads to small increases in annual mean PM 2.5 in the northeastern U.S. through increased sulfate from SO 2 oxidation Dawson et al, 2007b;Gonzalez-Abraham et al, 2014;Kelly et al, 2012;Trail et al, 2014) but there is no agreement on the magnitude. Trail et al (2014) find that higher temperatures lower OC and ammonium nitrate particles by favoring gas-phase partitioning.…”

“…Differences in modeling frameworks, including scenarios, simulation length, and the reported metrics, lead to a wide range in the estimated responses to climate change (Table S3). These studies show that at present-day emission levels, future climate change will degrade O 3 air quality over the U.S., especially over more polluted (high NO x ) areas, such as the U.S. Northeast, Southeast, Midwest, and southern California (Figures 8 and 9a; Gonzalez-Abraham et al, 2014, Hedegaard et al, 2013Kelly et al, 2012;Trail et al, 2014;val Martin et al, 2015;Fann et al, 2015). An increase in pollution episodes in the eastern U.S. has been tied to decreasing numbers of summertime frontal passages (Mickley et al, 2004;Leibensperger et al, 2008;Tai et al, 2012a), which may in turn be associated with a northward migration of the midlatitude jet stream (Barnes and Fiore, 2013).…”

“…CCM, regional climate model (RCM)-regional chemistry-transport model (RCTM), and GCM-CTM studies suggest that the impact of climate change on U.S. surface O 3 predominantly occurs in summer, with increases of up to 9 ppb over the eastern U.S. (Figures 8 and 9a; Gonzalez-Abraham et al, 2014;Kelly et al, 2012;Trail et al, 2014;val Martin et al, 2015). Many of these studies, however, analyzed a single scenario of short simulation length such that some of this range may reflect climate variability rather than the anthropogenic climate change signal (see Supplemental Text S2 and below).…”

“…The anthropogenic precursor emissions assumed in these studies usually follow either the SRES scenarios (e.g., Penrod et al, 2014) in which air pollutants and precursors span a wide future range, including increases (Prather et al, 2003), or RCP scenarios (e.g., Clifton et al, 2014) in which air pollutants and precursors decrease, with the exception of CH 4 in RCP8.5 ( Figure S2; Table S4). Alternative lower air pollutant emission projections are also considered (Gonzalez-Abraham et al, 2014;Trail et al, 2014). A few studies estimate future climate-driven emission increases in U.S. PM or O 3 from biogenic sources, wildfires, or anthropogenic land use (e.g., Gonzalez-Abraham et al, 2014;Penrod et al, 2014;val Martin et al, 2015).…”

“…Alternative lower air pollutant emission projections are also considered (Gonzalez-Abraham et al, 2014;Trail et al, 2014). A few studies estimate future climate-driven emission increases in U.S. PM or O 3 from biogenic sources, wildfires, or anthropogenic land use (e.g., Gonzalez-Abraham et al, 2014;Penrod et al, 2014;val Martin et al, 2015).…”