Transport analysis of ozone enhancement in Southern Ontario during BAQS-Met
1Air Quality Research Division, Science and Technology Branch, Environment Canada, Downsview, ON, Canada
2Department of Physics and Astronomy, University of Western Ontario, London, ON, Canada
3National Institute of Water and Atmospheric Research Ltd., Private Bag 14901, Kilbirnie, Wellington, New Zealand
4Department of Physics, University of Toronto, Toronto, ON, Canada
5ADNET Systems, Inc., GES DISC 610.2, NASA GSFC, Greenbelt, MD, USA
6Jet Propulsion Laboratory, NASA, Pasadena, CA, USA
7Department of Earth and Space Science and Engineering, York University, Toronto, ON, Canada
8Department of Chemistry and Atmospheric and Oceanic Sciences, McGill University, Montreal, QC, Canada
Abstract. Twice-daily ozonesondes were launched from Harrow, in southwestern Ontario, Canada, during the BAQS-Met (Border Air Quality and Meteorology Study) field campaign in June and July of 2007. A co-located radar windprofiler measured tropopause height continuously. These data, in combination with continuous surface ozone measurements and geo-statistical interpolation of satellite ozone observations, present a consistent picture and indicate that a number of significant ozone enhancements in the troposphere were observed that were the result of stratospheric intrusion events. The combined observations have also been compared with results from two Environment Canada numerical models, the operational weather prediction model GEM (as input to FLEXPART), and a new version of the regional air quality model AURAMS, in order to examine the ability of these models to accurately represent sporadic cross-tropopause ozone transport events. The models appear to reproduce intrusion events with some skill, implying that GEM dynamics (which also drive AURAMS) are able to represent such events well. There are important differences in the quantitative comparison, however; in particular, the poor vertical resolution of AURAMS around the tropopause causes it to bring down too much ozone in individual intrusions.
These campaign results imply that stratospheric intrusions are important to the ozone budget of the mid-latitude troposphere, and appear to be responsible for much of the variability of ozone in the free troposphere. GEM-FLEXPART calculations indicate that stratospheric ozone intrusions contributed significantly to surface ozone on several occasions during the BAQS-Met campaign, and made a moderate but significant contribution to the overall tropospheric ozone budget.