Unraveling the complex local-scale flows influencing ozone patterns in the southern Great Lakes of North America

Abstract

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 airquality model, AURAMS.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 the lake.Correspondence to: J. Brook (jeff.brook@ec.gc.ca) 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.

Exploring the nature of air quality over southwestern Ontario: main findings from the Border Air Quality and Meteorology Study

“…6) shows that when particle concentrations increased on 6 July there was a northwest to north flow crossing the Detroit and Windsor areas. Local emissions thus played a greater role during this part of the period compared to the first episode, but the location of their impact varied depending upon the synoptic wind direction and lake breezes (Levy et al, 2010). This is discussed further below.…”

“…The lake breeze from Lake Erie, as well as the prevailing synoptic winds, impacted the spatial and temporal heterogeneity in O 3 and PM 2.5 . Levy et al (2010) showed that emissions in the Detroit-Windsor area contributed significantly to the high O 3 at Harrow on the 6th with Lake Erie playing an important role. Under northerly winds the Detroit River and western Lake Erie first played a role early on the day by funnelling and accumulating the emissions and secondary products from the Detroit-Windsor area.…”

“…Passive, two-week average O 3 , NO 2 and NH 3 concentrations were measured using Ogawa samplers at all 16 mesonet sites, the West Windsor site and at the University of Windsor close to the international border crossing. The mesonet sites reporting O 3 are shown in Levy et al (2010) while the passive monitoring sites are shown in Lee et al (2011). During the IP, supersites were operated at Harrow, Bear Creek and Ridgetown with an enhanced suite of instrumentation (Fig.…”

“…Over-lake measurements of O 3 , SO 2 and black carbon (BC) were made on the ferry during scheduled daily passages between Pelee Island and the mainland between mid June to late August (Levy et al, 2010). The Canadian Regional and Urban Investigation System for Environmental Research (CRUISER) mobile laboratory drove in the region for 4-10 h day −1 during the intensive period following routes shown in Makar et al (2010b).…”

“…The BAQS-Met special issue of Atmospheric Chemistry and Physics contains 20 research papers (Chan et al, 2011;Ellis et al, 2011;Flagg and Taylor, 2011;Halla et al, 2011;Hayden et al, 2011;He at al., 2011;Lee et al, 2011;Levy et al, 2010;Jeong et al, 2010Jeong et al, , 2011Makar et al, 2010a, b;Markovic et al, 2011;Sills et al, 2011;Sjostedt et al, 2011;Slowik et al, 2011;Stroud et al, 2011Stroud et al, , 2012Wentzell et al, 2010) covering aspects of regional particle physics, chemistry and source apportionment, secondary organic and inorganic particle formation, the influence of the lakes on ozone and particles; lake breeze kinematics and behaviour, remote measurements (surface and satellite) of NO 2 and AOD and high-resolution meteorological modelling of regional air quality. The intent of the current paper is to describe the objectives and the main hypotheses considered by the BAQS-Met study and the main results.…”