and ammonia (NH3). The relationships between direct emissions and ambient concentrations are not linear and involve large transport distances, thereby complicating air quality management.

China has focused on directly emitted PM and SO2 emissions and concentrations, with less regulatory attention being given to secondary pollutants such as O3 or the sulfate, nitrate, and ammonium components of PM. China has made great progress over the last 25 to 30 years in reducing emissions per unit of fuel use or production. However, rapid growth in all energy sectors means more fuel use and product, which counteracts reductions for individual units. Shuttering obsolete facilities, which are often the most offensive polluters, has been an effective strategy, as well as adopting modern engine designs and requiring cleaner fuels (e.g., low sulfur coal). While necessary measures, these represent the “low-hanging fruit,” and greater reductions for a larger number of emitters and economic sectors will be needed to attain healthful air quality. The responsibility for developing and instituting many air quality and energy strategies rests with local and regional governments. The importance of national policies and actions should not be overlooked, but the most appropriate solutions in China will require local knowledge, willpower, and implementation.

To examine the challenges faced today by China and the United States in terms of energy use and urban air pollution, the U.S. National Academies, in cooperation with the Chinese Academy of Engineering and the Chinese Academy of Sciences, developed this comparative study. In addition to informing national policies in both countries, the study is intended to assist Chinese cities in assessing their challenges, which include meeting increased energy demands, managing the growth in motor vehicle use, and improving air quality, all while maintaining high rates of economic growth. This report is geared towards policy and towards decision makers involved in urban energy and air quality issues. It identifies lessons learned from the case studies of four cities (Pittsburgh and Los Angeles in the United States, Huainan and Dalian in China), addresses key technological and institutional challenges and opportunities, and highlights areas for continued cooperation between the United States and China. Owing to the small number of case studies, the committee decided against making many recommendations specifically tailored to the case study cities, or to cities in general, based solely on the experience of the four case studies. Instead, the case studies provide insight into how energy use and air quality are managed at a local level, and how our cities might learn from one another’s experience. This study does not examine in detail the related and increasingly significant issue of global climate change. It does acknowledge that this will be a central issue in future discussions of energy and air pollution, and an area where continued cooperation between the U.S. and Chinese Academies will be critical. The study committee, composed of leading experts on energy and air quality from both countries, began its work in 2005.

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