Abstract
Abstract. We use a global coupled chemistry–climate–land model (CESM) to assess the integrated effect of climate, emissions and land use changes on annual surface O3 and PM2.5 in the United States with a focus on national parks (NPs) and wilderness areas, using the RCP4.5 and RCP8.5 projections. We show that, when stringent domestic emission controls are applied, air quality is predicted to improve across the US, except surface O3 over the western and central US under RCP8.5 conditions, where rising background ozone counteracts domestic emission reductions. Under the RCP4.5 scenario, surface O3 is substantially reduced (about 5 ppb), with daily maximum 8 h averages below the primary US Environmental Protection Agency (EPA) National Ambient Air Quality Standards (NAAQS) of 75 ppb (and even 65 ppb) in all the NPs. PM2.5 is significantly reduced in both scenarios (4 μg m−3; ~50%), with levels below the annual US EPA NAAQS of 12 μg m−3 across all the NPs; visibility is also improved (10–15 dv; >75 km in visibility range), although some western US parks with Class I status (40–74 % of total sites in the US) are still above the 2050 planned target level to reach the goal of natural visibility conditions by 2064. We estimate that climate-driven increases in fire activity may dominate summertime PM2.5 over the western US, potentially offsetting the large PM2.5 reductions from domestic emission controls, and keeping visibility at present-day levels in many parks. Our study indicates that anthropogenic emission patterns will be important for air quality in 2050. However, climate and land use changes alone may lead to a substantial increase in surface O3 (2–3 ppb) with important consequences for O3 air quality and ecosystem degradation at the US NPs. Our study illustrates the need to consider the effects of changes in climate, vegetation, and fires in future air quality management and planning and emission policy making.
Highlights
Air pollution, such as surface ozone (O3) and fine particulate matter, has evolved in both urban and rural regions around the world over the last centuries
Under RCP8.5 conditions, we find an improvement of surface O3 air quality for most polluted days, except in the Great Plains region, and a deterioration in the background O3 all across the United States
We have quantified for the first time changes in air quality between the present and a 2050 future period associated with changes in emissions, climate, and land use change over the United States
Summary
Air pollution, such as surface ozone (O3) and fine particulate matter (with diameter < 2.5 μm; PM2.5), has evolved in both urban and rural regions around the world over the last centuries. Air pollution changes have resulted in part from direct changes in natural and anthropogenic emissions and in part from indirect changes associated with climate and land use (Jacob and Winner, 2009; Arneth et al, 2010; Fiore et al, 2012). We examine the integrated effect of climate change, anthropogenic emission changes, and land use change on air quality over the United States, with a particular focus on the US national parks. To our knowledge, this is the first time that the relative effect of these three factors has been considered for US air quality projection. We assess the changes in surface O3 and PM2.5 in 2050 relative to present-day levels and discuss the meteorological and chemical drivers behind these changes
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