Atmos. Chem. Phys. Discuss., 10, 14241-14312, 2010
www.atmos-chem-phys-discuss.net/10/14241/2010/
doi:10.5194/acpd-10-14241-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Mass tracking for chemical analysis: the causes of ozone formation in southern Ontario during BAQS-Met 2007
P. A. Makar1, J. Zhang1, W. Gong1, C. Stroud1, D. Sills2, K. L. Hayden1, J. Brook1, I. Levy1, C. Mihele1, M. D. Moran1, D. W. Tarasick1, and H. He1
1Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada
2National Laboratory for Nowcasting and Remote Sensing Meteorology, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada

Abstract. A three-level nested regional air pollution model has been used to study the processes leading to high ozone concentrations in the southern Great Lakes region of North America. The highest resolution simulations show that complex interactions between the lake breeze circulation and the synoptic flow lead to significant enhancements in the photochemical production and transport of ozone at the local scale. Significant improvements in model correlation with ozone observations are achieved in going to the highest spatial resolution. Mass tracking of individual model processes show that Lakes Erie and St. Clair frequently act as photochemical production regions, with average mid-day production rates of 6 to 8 ppbv per hour. Enhanced ozone levels are evident over these two lakes in 23-day-average surface ozone fields. Analysis of other model fields and aircraft measurements suggests that vertical recirculation enhances ozone levels over Lake St. Clair while strong subsidence enhances ozone over Lake Erie. The mass tracking of model transport shows that lake-breeze surface convergence zones combined with the synoptic flow can carry ozone and its precursors hundreds of kilometers from these source areas, in narrow, elongated features. Comparison with surface mesonet ozone observations confirm the presence, magnitude, and timing of these features, which create local ozone enhancements on the order of 20 ppbv above the regional ozone levels. High-resolution modelling is recommended in order to predict these local-scale features in operational air-quality forecasts.

Citation: Makar, P. A., Zhang, J., Gong, W., Stroud, C., Sills, D., Hayden, K. L., Brook, J., Levy, I., Mihele, C., Moran, M. D., Tarasick, D. W., and He, H.: Mass tracking for chemical analysis: the causes of ozone formation in southern Ontario during BAQS-Met 2007, Atmos. Chem. Phys. Discuss., 10, 14241-14312, doi:10.5194/acpd-10-14241-2010, 2010.
 
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