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The impact of temperature on formation of O3 and odd nitrogen photochemistry is investigated using urban-, regional- and global-scale simulations. Urban and polluted rural environments are explored with a regional simulation derived from a specific episode in the midwestern United States. The simulations predict that O3 increases with temperature in both urban and polluted rural environments. The O3-temperature relation is driven largely by chemistry of peroxyacetylnitrate (PAN) which represents an increased sink for both NOx and odd hydrogen at low temperatures. Isoprene emissions, H2O, and solar radiation also contribute to the O3-temperature relation. Possible correlations between temperature and anthropogenic emissions or stagnant meteorology were not included. Observations at urban and rural sites in the United States suggests that O3 increases with temperature at a faster rate than the models predict. Calculations with a one-dimensional global model suggest that increased temperature in the polluted boundary layer does not lead to increased O3 in the free troposphere, because increased export of O3 is balanced by decreased export of odd nitrogen species.