Abstract
Abstract. Quantifying trends in surface ozone concentrations is critical for assessing pollution control strategies. Here we use observations and results from a global chemical transport model to examine the trends (1991–2005) in daily maximum 8-h average concentrations in summertime surface ozone at rural sites in Europe and the United States (US). We find a decrease in observed ozone concentrations at the high end of the probability distribution at many of the sites in both regions. The model attributes these trends to a decrease in local anthropogenic ozone precursors, although simulated decreasing trends are overestimated in comparison with observed ones. The low end of observed distribution show small upward trends over Europe and the western US and downward trends in Eastern US. The model cannot reproduce these observed trends, especially over Europe and the western US. In particular, simulated changes between the low and high end of the distributions in these two regions are not significant. Sensitivity simulations indicate that emissions from far away source regions do not affect significantly summer ozone trends at both ends of the distribution in both Europe and US. Possible reasons for discrepancies between observed and simulated trends are discussed.
Highlights
Quantifying surface ozone (O3) concentrations and associated trends is critical for understanding the processes influencing tropospheric O3 budget and assessing pollution control strategies (Lin et al, 2000; Vingarzan, 2004)
Current trends are not geographically uniform, recent studies report declining trends in O3 concentrations at urban sites and at sites downwind of urban centers in North America and Europe (Vingarzan, 2004; Martien and Harley, 2006; Logan et al, 2012; Wilson et al, 2012, and references therein). These declines are more evident at the high end of the ozone probability distribution and appear to be associated with declining local ozone precursor emissions (Bronnimann et al, 2002; Vingarzan, 2004; Jonson et al, 2006; Logan et al, 2012)
The observed O3 concentrations are decreasing at the high end of the probability distribution in the majority of the examined sites in both regions, which is very likely related to the decrease in local O3 precursor emissions
Summary
Quantifying surface ozone (O3) concentrations and associated trends is critical for understanding the processes influencing tropospheric O3 budget and assessing pollution control strategies (Lin et al, 2000; Vingarzan, 2004). Current trends are not geographically uniform, recent studies report declining trends in O3 concentrations at urban sites and at sites downwind of urban centers in North America and Europe (Vingarzan, 2004; Martien and Harley, 2006; Logan et al, 2012; Wilson et al, 2012, and references therein) These declines are more evident at the high end of the ozone probability distribution and appear to be associated with declining local ozone precursor emissions (Bronnimann et al, 2002; Vingarzan, 2004; Jonson et al, 2006; Logan et al, 2012). The origins of this increase in ozone background are still unclear (Bronnimann et al, 2002; Jonson et al, 2006) but some of the plausible factors include changes in ozone precursor emissions with subsequent long range transport, change in stratospheric-tropospheric exchange, and global rise in methane levels (Lin et al, 2000; Vingarzan, 2004; Jonson et al, 2006; Ordonez et al, 2007; Fiore et al, 2009)
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