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2015 Ozone NAAQS Attainment Challenge For Lake Michigan Basin

Reaching attainment with the National Ambient Air Quality Standard (NAAQS) for ozone has proven to be a vexing issue for areas near the shores of Lake Michigan, despite substantial reductions in precursor emissions over the past several decades and will prove to be even more difficult with the adoption of the 2015 standard.

The following map depicts the areas designated as nonattainment with the 2015 ozone standard:

In the past ten years, (2007 – 2017) anthropogenic VOC emissions in the four states have been reduced by 28 percent; NOx emissions have been reduced by 45 percent. Industrial sources including the utility sector currently account for approximately 30 percent of the total NOx emissions in the four-state area; less than 20 percent of the total VOC emissions in the four-state area.

Despite these precursor emission reductions, EPA’s data for ozone design values in counties adjacent to the lake have only decreased on average by 14 percent during this same period, with individual monitoring sites seeing reductions of 8 to 22 percent. In Illinois lakeshore counties, ozone levels have been reduced by only slightly more than 9 percent, while in Wisconsin lakeshore counties, the reduction has been just over 13 percent, and in both Indiana and Michigan, the reduction has been more than 16 percent. The lowest reductions in the region have been experienced at lakeshore monitors located near the Illinois – Wisconsin state line (Illinois Beach State Park and the Chiwaukee Prairie State Line monitoring sites).

The following graphic shows the annual emissions in the four-state area along with fourth-high measured ozone concentrations in lakeshore counties, used to determine attainment with the standard:

To address the science of ozone formation and impacts in the Lake Michigan basin, and the issues with respect to the ability of available models to provide more accurate predictions of ozone concentrations, the Lake Michigan Ozone Study 2017 was conducted during May and June 2017. The objectives of this study included the following:

• Quantify the relative contributions of inter- and intra-state precursor emissions and emission sources on ozone production along Lake Michigan;
• Evaluate and improve the meteorological and chemical transport models;
• Study the link between lake breeze circulations and ozone concentrations;
• Analyze the causes of concentration differences between coastal and inland monitoring sites; and
• Develop best practices for ozone attainment planning models

Whether the region can ultimately reach attainment in the coming years remains uncertain. Hopefully, this latest study will provide a roadmap to attainment.

Zac Adelman, the Executive Director of the Lake Michigan Air Director’s Consortium (LADCO) will be discussing observations and preliminary results of this study. In addition, John Mooney, Chief, Air Programs Branch, EPA Region V, will be discussing the implications of ozone nonattainment for the Lake Michigan states, and potential regulatory implications that may result from the findings of the study.

Author: David F. Seitz, P.E. (WI, SC)
Senior Client Service Manager
TRC Environmental Corp.
(262) 901-2141


[1] Zac Adelman, Lake Michigan Air Directors Consortium; Lake Michigan Ozone Study; presented at the Federation of Environmental Technologists Annual Conference; October 26, 2017