Global air quality and climate

International audienceEmissions of air pollutants and their precursors determine regional air quality and can alter climate. Climate change can perturb the long-range transport, chemical processing, and local meteorology that influence air pollution. We review the implications of projected changes in methane (CH 4), ozone precursors (O 3), and aerosols for climate (expressed in terms of the radiative forcing metric or changes in global surface temperature) and hemispheric-to-continental scale air quality. Reducing the O 3 precursor CH 4 would slow near-term warming by decreasing both CH 4 and tropospheric O 3. Uncertainty remains as to the net climate forcing from anthropogenic nitrogen oxide (NO x) emissions, which increase tropospheric O 3 (warming) but also increase aerosols and decrease CH 4 (both cooling). Anthropogenic emissions of carbon monoxide (CO) and non-CH 4 volatile organic compounds (NMVOC) warm by increasing both O 3 and CH 4. Radiative impacts from secondary organic aerosols (SOA) are poorly understood. Black carbon emission controls, by reducing the absorption of sunlight in the atmosphere and on snow and ice, have the potential to slow near-term warming, but uncertainties in coincident emissions of reflective (cooling) aerosols and poorly constrained cloud indirect effects confound robust estimates of net climate impacts. Reducing sulfate and nitrate aerosols would improve air quality and lessen interference with the hydrologic cycle, but lead to warming. A holistic and balanced view is thus needed to assess how air pollution controls influence climate; a first ste