Abstract

Multiple linkages connect air quality and climate change. Many air pollutant sources also emit carbon dioxide (CO₂), the dominant anthropogenic greenhouse gas (GHG). The two main contributors to non-attainment of U.S. ambient air quality standards, ozone (O₃) and particulate matter (PM), interact... Show moreMultiple linkages connect air quality and climate change. Many air pollutant sources also emit carbon dioxide (CO₂), the dominant anthropogenic greenhouse gas (GHG). The two main contributors to non-attainment of U.S. ambient air quality standards, ozone (O₃) and particulate matter (PM), interact with radiation, forcing climate change. PM warms by absorbing sunlight (e.g., black carbon) or cools by scattering sunlight (e.g., sulfates) and interacts with clouds; these radiative and microphysical interactions can induce changes in precipitation and regional circulation patterns. Climate change is expected to degrade air quality in many polluted regions by changing air pollution meteorology (ventilation and dilution), precipitation and other removal processes, and by triggering some amplifying responses in atmospheric chemistry and in anthropogenic and natural sources. Together, these processes shape distributions and extreme episodes of O₃ and PM. Global modeling indicates that as air pollution programs reduce SO₂ to meet health and other air quality goals, near-term warming accelerates due to “unmasking” of warming induced by rising CO₂. Air pollutant controls on CH₄, a potent GHG and precursor to global O₃ levels, and on sources with high black carbon (BC) to organic carbon (OC) ratios could offset near-term warming induced by SO₂ emission reductions, while reducing global background O₃ and regionally high levels of PM. Lowering peak warming requires decreasing atmospheric CO₂, which for some source categories would also reduce co-emitted air pollutants or their precursors. Model projections for alternative climate and air quality scenarios indicate a wide range for U.S. surface O₃ and fine PM, although regional projections may be confounded by interannual to decadal natural climate variability. Continued implementation of U.S. NOx emission controls guards against rising pollution levels triggered either by climate change or by global emission growth. Improved accuracy and trends in emission inventories are critical for accountability analyses of historical and projected air pollution and climate mitigation policies. Show less