Impact of temperature on oxidant photochemistry in urban, polluted rural and remote environments

Abstract

The impact of temperature on formation of O 3 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 O 3 increases with temperature in both urban and polluted rural environments. The O 3‐temperature relation is driven largely by chemistry of peroxyacetylnitrate (PAN) which represents an increased sink for both NO x and odd hydrogen at low temperatures. Isoprene emissions, H 2 O, and solar radiation also contribute to the O 3‐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 O 3 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 O 3 in the free troposphere, because increased export of O 3 is balanced by decreased export of odd nitrogen species.