The role of climate-ecosystem interactions on summer time ground level ozone pollution in North America

Thursday, 18 December 2014
Sarah Kavassalis and Jennifer G Murphy, University of Toronto, Chemistry, Toronto, ON, Canada
The drivers of day-to-day and interannual variability in ground level ozone concentrations are often difficult to identify. Traditionally, analyses of variability in ozone pollution, especially in urban settings, have been focused on the factors that influence the production of ozone, specifically precursor emissions and favourable meteorological conditions. However, factors that govern the sinks of ozone can also strongly impact average and extreme concentrations. Based on a statistical analysis of 20 years of ground level ozone data in the United States and Canada, we observe that, in many regions, a significant amount of that variability can be attributed to climate-ecosystem interactions. In rural and urban environments with high leaf area indices (LAI), daily ground level ozone concentrations are strongly associated with vapor pressure deficit and soil moisture in the summer, suggesting that reduced stomatal conductance is a significant factor in summer time ozone episodes. We propose that the role of a meteorologically dependent vegetative dry deposition sink for ozone has been underappreciated in the interpretation of ambient ozone data from North America. The role of vapour pressure deficit in controlling ozone in highly vegetative urban regions, like the Southeastern US, is especially significant. The strength of this correlation in the observational record suggests that this interaction may be important to properly represent in chemistry-climate projections.