A Preliminary Synthesis of Modeled Climate Change Impacts on U.S. Regional Ozone Concentrations

D iscussion of the potential sensitivity of air quality to climate change has increased in recent years. In 2001, the NRC (acronyms defined in Table 1) posed the question “to what extent will the United States be in control of its own air quality in the coming decades?” noting that “. . . changing climatic conditions could significantly affect the air quality in some regions of the United States . . .” and called for the expansion of air quality studies to include investigation of how U.S. air quality is affected by long-term climatic changes (NRC 2001). A subsequent NRC report emphasized that the U.S. air quality management system must be “flexible and vigilant” to ensure the effectiveness of pollution mitigation strategies in the face of climate change (NRC 2004). The recent IPCC Fourth Assessment Report warned of the possibility of significant air quality degradation in some regions as a result of climate-related changes in the dispersion rate of pollutants, the chemical environment for O3 and aerosol generation, and the strength of emissions from the biosphere, fires, and dust (Solomon et al. 2007). The mission of the EPA is to protect human health and the environment. To achieve this mission, the EPA implements a variety of programs under the Clean Air Act that reduces ambient concentrations of air pollutants. Pollutants such as O3 are not emitted directly into the atmosphere; instead, they are created by chemical reactions between NOx and VOCs in the presence of heat and sunlight. These pollutants are emitted from a variety of sources, including motor vehicles, chemical and power plants, refineries, factories, and consumer and commercial products, as well as natural sources, such as vegetation, lightning, and biological processes in the soil. The EPA’s efforts have been successful: between 1980 and 2007, emissions of VOCs and NOx decreased by 50% and 39%, respectively, even though the gross domestic product increased 124%, vehicle miles traveled increased 103% and energy consumption increased 30% (U.S. EPA 2008). Air pollution, however, including O3 pollution, continues to be a widespread public health and environmental problem in the United States, with peak-level O3 concentrations in numerous counties still exceeding the NAAQS for O3, 1 and with health effects ranging from increased mortality to chronic effects on respiratory and cardiovascular health (e.g., see Jerrett et al. 2009). A PRELIMINARY SYNTHESIS OF MODELED CLIMATE CHANGE IMPACTS ON U.S. REGIONAL OZONE CONCENTRATIONS