Unraveling the complex local-scale flows influencing ozone patterns in the southern Great Lakes of North America 1Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada
22 Nov 2010
2Cloud Physics and Severe Weather Research Section, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada
Received: 09 July 2010 – Published in Atmos. Chem. Phys. Discuss.: 23 August 2010 Abstract. This study examines the complexity of various processes influencing
summertime ozone levels in the southern Great Lakes region of North America.
Results from the Border Air Quality and Meteorology (BAQS-Met) field
campaign in the summer of 2007 are examined with respect to land-lake
differences and local meteorology using a large array of ground-based
measurements, aircraft data, and simulation results from a high resolution
(2.5 km) regional air-quality model, AURAMS.
Revised: 02 November 2010 – Accepted: 15 November 2010 – Published: 22 November 2010
Analyses of average ozone mixing ratio from the entire BAQS-Met intensive
campaign period support previous findings that ozone levels are higher over
the southern Great Lakes than over the adjacent land. However, there is
great heterogeneity in the spatial distribution of surface ozone over the
lakes, particularly over Lake Erie during the day, with higher levels
located over the southwestern end of the lake. Model results suggest that
some of these increased ozone levels are due to local emission sources in
large nearby urban centers. While an ozone reservoir layer is predicted by
the AURAMS model over Lake Erie at night, the land-lake differences in ozone
mixing ratios are most pronounced during the night in a shallow inversion
layer of about 200 m above the surface. After sunrise, these differences
have a limited effect on the total mass of ozone over the lakes and land
during the day, though they do cause elevated ozone levels in the
lake-breeze air in some locations.
The model also predicts a mean vertical circulation during the day with an
updraft over Detroit-Windsor and downdraft over Lake St. Clair, which
transports ozone up to 1500 m above ground and results in high ozone over
Oscillations in ground-level ozone mixing ratios were observed on several
nights and at several ground monitoring sites, with amplitudes of up to 40 ppbv
and time periods of 15–40 min. Several possible mechanisms for
these oscillations are discussed, but a complete understanding of their
causes is not possible given current data and knowledge.
Citation: Levy, I., Makar, P. A., Sills, D., Zhang, J., Hayden, K. L., Mihele, C., Narayan, J., Moran, M. D., Sjostedt, S., and Brook, J.: Unraveling the complex local-scale flows influencing ozone patterns in the southern Great Lakes of North America, Atmos. Chem. Phys., 10, 10895-10915, doi:10.5194/acp-10-10895-2010, 2010.