Regional and Global Emissions of Air Pollutants: Recent Trends and Future Scenarios

New scientific understanding could increase the cost-effectiveness of local and regional air quality management policies, enhance the acceptance of mitigation measures for long-lived greenhouse gas (GHG) emissions, and reveal win-win portfolios of controls for short-lived substances that yield immediate health and crop benefits while limiting temperature increase in the near term. However, although substantial efforts have been devoted to global analyses of the emissions of carbon dioxide (CO 2 ) and other long-lived GHGs, air pollutant emissions have received only limited attention in the global context. Past and likely future trends in air pollutant emissions evolve rather differently from those of long-lived GHGs, so that superficial extrapolations of GHG trends would lead to misleading conclusions. In many world regions, the evolution of air pollutant emissions has effectively decoupled from economic growth. Since 1990, air pollutant emissions declined (sulfur dioxide, SO 2 ), stabilized (nitrogen oxides, NO x ), or increased slightly (black carbon, BC; organic carbon, OC; and ammonia, NH 3 ). This review discusses to what extent structural changes, technological improvements, and dedicated environmental legislation have contributed to these changes. The scenarios of future emissions in the literature span a wide range, mainly owing to different assumptions about future environmental policies. Although the more recent scenarios agree on declining air pollutants up to 2030, avoiding potential rebounds of emissions after 2030 will require additional policy interventions.