The U.S. Environmental Protection Agency (EPA), as part of its Science to Achieve Results (STAR) program, is seeking applications for Air, Climate and Energy (ACE) Centers. EPA is interested in supporting research on the development of sound science to systematically inform policy makers at the state and local levels regarding the development of innovative approaches to enable effective implementation of air pollution control strategies to achieve the greatest public health benefits by reducing exposure to harmful air pollution. Priority research areas include: 1) enhancing understanding of spatial and temporal differences in individual pollutants and pollutant mixtures within and across different areas (including urban areas, or between urban, suburban, and rural areas) or geographic regions; 2) identifying and improving the characterization of the most important factors contributing to regional or city-to-city differences or similarities in air pollution and health effects beyond topography and meteorology; 3) improving the ability to understand and project how these contributing factors and differences may change over the next one to several decades; and 4) advancing scientific knowledge and tools needed to develop robust strategies for air pollution control to improve public and environmental health under a variety of conditions, including consideration of approaches for addressing climate change preparedness.