Assessment of Ozone Production and Accumulation over Lake Michigan

High ozone concentrations along the shores of Lake Michigan remain a challenge for the states surrounding the lake. Previous field studies have indicated that the transport of ozone precursors from urban centers to areas over the lake allows ozone production and accumulation within the shallow boundary layer over water, and a return flow due to Lake Breeze bring the elevated ozone back onshore and over the population centers. Yet, models continue to have difficulty in realizing the complex interactions of meteorology, emissions, and atmospheric chemistry in this region.

In the current study, the average summertime behavior of flow field and chemistry over the lake is analyzed. In particular, the role of model mixing and lake surface temperatures are examined in terms of changing stability over the lake. The results from air quality simulations over summers of 2009, 2011, and 2013 are used to ascertain the key factors impacting ozone production and accumulation over the lake. The results indicate that while there are pronounced similarities in the average flow field and spatial variation of ozone over the Lake Michigan, the strength of the predominant westerlies, land/water temperature contrast, and the curvature of the shoreline determine the onset of land breeze and the location of a divergence zone near the lake surface that is prone to high ozone production.

Furthermore, a series of model experiments were performed utilizing satellite-derived insolation, skin temperature to adjust moisture, and MODIS lake temperature in the model. The results indicate significant improvement in 2-m temperature and moisture. Additionally, this study revealed that an over/under-estimation of vertical mixing in the offline meteorological model can lead to an under/over-estimation of mixing in the photochemical model. The role of vertical mixing over the lake impacting higher surface ozone will be discussed.