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

Abstract

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.

Impacts of weather conditions modified by urban expansion on surface ozone: Comparison between the Pearl River Delta and Yangtze River Delta regions

“…Areas with the main O 3 concentration increases generally coincide with the areas of temperature increases and wind speed reductions. These results are consistent with previous studies showing the direct link between increased ozone concentrations and higher temperatures (Sillman and Samson, 1995;Aw and Kleeman, 2003). Nevertheless, it should be noted that, in the daytime, the surface ozone increase (by 2.9%-4.2%) is less than that for the nighttime (about 4.7%-8.5%).…”

U.S. Ozone Air Quality under Changing Climate and Anthropogenic Emissions

“…Despite substantial progress toward O 3 pollution control in the U.S. there remain nonattainment areas (http://www.epa.gov/oar/oaqps/greenbk/ map8hrnm.html). Although changes in U.S. anthropogenic emissions will likely play the key role in future U.S. O 3 air quality, the effects of changes in climate, methane (CH 4 ) abundance, and non-U.S. anthropogenic emissions cannot be discounted. While the net effect of future climate change alone is a decrease in the global tropospheric O 3 due to increased absolute humidity (1)(2)(3), there could be groundlevel O 3 increases in some polluted regions due to increased NO x under warmer temperatures (4), increased biogenic volatile organic compounds (VOCs) emissions (5-7), and circulation changes (8)(9)(10).…”

“…Non-U.S. anthropogenic emissions affect U.S. O 3 concentrations by influencing the U.S. O 3 background (11) which, for example, contributes an average 15-30 ppbv to afternoon O 3 mixing ratios in surface air in the eastern U.S. and 25-35 ppbv in the western U.S. (based on model simulations (12) for the summer of 1995). Thus, future increases in non-U.S. anthropogenic emissions, especially CH 4 (13,14) and nitrogen oxides (NO x ), could increase U.S. O 3 concentrations.…”

“…For example, some studies find that anthropogenic emissions changes (U.S. and worldwide) will influence future U.S. O 3 air quality the most (16), others find that climate change will play an equallysif not moresinfluential role (5,10); others point to reductions in CH 4 emissions as a cost-effective method of achieving both global (and U.S.) O 3 air quality and climate objectives (14). Thus, there is a need for analyses that consider the multitude of factors influencing future U.S. air quality under a common framework.…”

“…Since we have previously analyzed in some detail the O 3 effects of climate change under present-day emissions at global and regional (U.S.) scales (see; Racherla and Adams (3,7); hereafter referred to as RA2006 and RA2008, respectively), we focus here on the combined effects of changes in climate and anthropogenic emissions worldwide. We do not perform a detailed scenario analysis of the O 3 effects of CH 4 and non-U.S. emissions, but focus instead on quantifying their role in a high-emissions scenario.…”