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Air pollution contributes to adverse health outcomes.Approximately 121 million people in the United States—one third of the population—live where National Ambient Air Quality Standards (NAAQS) are violated. In most cases, the criteria pollutants exceeding standards are ozone (O3) and fine particles (PM2.5). In addition, 188 substances known or suspected to cause cancer or other serious health effects are designated as hazardous air pollutants (HAPs). Essentially, all O3 and significant portions of PM2.5 and HAPs are produced in the atmosphere through chemical and physical processes. In the case of PM2.5, subcomponents formed primarily from precursor gases—sulfate, nitrate, ammonium, and secondary organic aerosol (SOA)—account for 60% of the U.S. county-level annual mean concentration. In addition, 47% of the cancer risk and 25% of the noncancer risk from HAPs have been attributed to atmospheric chemistry rather than direct emissions. In this article, we introduce the role of chemical mechanisms in air quality models, a new atmospheric science community effort, and needs for further mechanism development.

We utilize clinical records of successive visits by children to pediatric clinics in Indianapolis to estimate the effects on their body mass of environmental changes near their homes. We compare results for fixed-residence children with those for cross-sectional data. Our environmental factors are fast food restaurants, supermarkets, parks, trails, and violent crimes, and 13 types of recreational amenities derived from the interpretation of annual aerial photographs. We looked for responses to these factors changing within buffers of 0.1, 0.25, 0.5, and 1 mile. We found that cross-sectional estimates are quite different from the Fixed Effects estimates of the impacts of amenities locating near a child. In cross section nearby fast food restaurants were associated with higher BMI and supermarkets with lower BMI. These results were reversed in the FE estimates. The recreational amenities that appear to lower children's BMI were fitness areas, kickball diamonds, and volleyball courts. We estimated that locating these amenities near their homes could reduce the weight of an overweight eight-year old boy by 3 to 6 pounds.