Characterization and Mitigation Strategies for Chicago Air Quality

Abstract:

Sustained efforts to improve air quality in the U.S. have successfully decreased air pollutant emissions, however, many urban areas still struggle to comply with EPA air quality standards. This situation is exemplified by the city of Chicago, which has been in 8-hour ozone (O₃) non-attainment since 2012. Within the city itself, high-emission sources and fine-scale meteorological interactions result in spatiotemporal heterogeneity in pollutant concentrations. These pollutant hotspots can be characterized through a combination of high-resolution air quality datasets so that informed policy can alleviate the unequal pollutant exposure of vulnerable citizenry.

To identify Chicagoland pollutant hotspots and assess potential control measures, this study utilizes three air quality products: 1.3 km simulations of the WRF-CMAQ model, the satellite-based instrument TropOMI, and EPA air quality monitors. Historical case-study WRF-CMAQ simulations allow for comparison with EPA monitors and TropOMI and facilitate identification of meteorological controls, sensitivities, and biases over the simulation. Our simulations agree with satellite column (R² = 0.7 for NO₂) and surface measurements (R² = 0.9 for NO₂, R² = 0.9 for O₃), though is biased high for surface O₃. We show that NO₂ is concentrated near high emissions sources, such as highways, while O₃ concentrations are inversely related to NO₂. Fine-scale variations in air quality are influenced by the lake-breeze and urban heat island, with spatiotemporal changes transporting emissions from sources.

Building off this characterization, we target Chicago’s NO₂ pollution corridors by modeling an electrified transportation sector using WRF-CMAQ. To create a feasible electrification plan, we remove emissions from Chicago’s municipal vehicle fleet (transit buses, school buses and refuse trucks) and personal vehicles. The electrification of municipal vehicles results in an average 2% decrease of NO₂ concentrations, though this scenario increases O₃ by 1.2% and has spatially heterogeneous changes in particulate matter species. This research provides a framework for a mitigation strategy and cost-benefit analysis by city planners to assess the transition between the current transportation paradigm and one that can support Chicago’s sustainability goals.