In 2019, Chicago’s average air quality index (AQI) was 52 (“moderate”).[1] The Environmental Protection Agency (EPA) defines “moderate” air quality as acceptable air quality, but for some pollutants, there may be a moderate health concern to a small number of individuals.[2] AQI ratings are calculated by weighing six key criteria pollutants for their risk to health: (1) ozone, (2) particulate matter, (3) carbon monoxide, (4) nitrogen dioxide), (5) sulfur dioxide, and (6) lead.[3] Particulate matter includes both PM10 and PM2.5, which are the numbers referring to the particle’s diameter in micrometers.[4] Of the six criteria pollutants measured, the pollutant with the highest individual AQI becomes the “main pollutant” and dictates the overall AQI for a location.[5] Two of the most common pollutants responsible for a city’s AQI, due to the weight the formula ascribes to them and their potential harm, are PM2.5 and ozone.[6]

On March 24, 2021, the City of Chicago passed an Air Quality Ordinance. The ordinance regulates the construction and expansion of certain industrial facilities that cause or contribute to air pollution.[7]  It requires a formal review process and expanded public engagement opportunities during this process.[8] Specifically, site plans must include a traffic study and an air quality impact study, and be submitted and approved by the Department of Planning and Development (DPD), the Chicago Department of Public Health (CDPH), and the Chicago Department of Transportation (CDOT).[9]


The biggest glaring issue with the Air Quality Ordinance is that it does not outline the criteria the air quality impact study should include, specifically the level of detail and analysis, to satisfy the ordinance, nor does it outline any criteria the City must adhere to when evaluating the study.[10] Additionally, it doesn’t specify the authority the review agencies have to mandate revisions to the environmental studies, reject the studies outright on substantive grounds, or require mitigating measures if studies show elevated levels of impacts on the surrounding communities.[11]  Finally, as currently drafted, it is not clear the Air Quality Ordinance allows City officials to mandate any air quality mitigation measures above those that may be required under any federal or state air quality permits.[12]

The takeaway is that the studies required under the Air Quality Ordinance will impose additional costs and planning time on developers of facilities subject to the ordinance, and unless amended, will likely open the ordinance up to void for vagueness challenges.


[1] Air Quality in Chicago, IQAir, (last visited Nov. 26, 2021), [].

[2] Air Data Basic Information, United States Environmental Protection Agency, (last visited Nov. 26, 2021), [].

[3] Id.

[4] Id.

[5] See Air Quality in Chicago, supra note 1.

[6] Id.

[7] Chicago Air Quality Ordinance, City of Chicago, (last visited Nov. 26, 2021), [].

[8] Id.

[9] Id.

[10] Donna J. Pugh, et al., New Chicago Air Quality Zoning Ordinance Adds Environmental Review Process; Public Participation Requirements, Foley & Lardner LLP, (last visited on Nov. 26, 2020), [].

[11] Id.

[12] Id.