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Westchester, Illinois, nestled within Cook County, occupies a geographically strategic position within the broader Chicago metropolitan area. Located approximately 25 miles northwest of downtown Chicago, the city’s terrain is predominantly flat, characteristic of the Illinois River Valley, with elevations rarely exceeding 700 feet above sea level. This flatness, while facilitating development, can also contribute to air quality challenges, particularly during temperature inversions. The surrounding landscape is a blend of agricultural fields and suburban development, reflecting the urban–rural gradient common to the region. Westchester sits within the footprint of the historic Chicago and Northwestern Railroad corridor, a legacy of industrial and transportation activity that, while diminished, still influences local land use patterns. The proximity to the Des Plaines River, though not directly bordering the city, influences local microclimates and can impact humidity levels, which in turn affects pollutant dispersion. While not directly adjacent to major industrial belts, Westchester’s location within the Chicago metropolitan area means it is indirectly influenced by emissions from larger industrial zones to the south and east. The city’s suburban character, with a mix of residential areas, commercial strips, and light industrial zones, contributes to a localized pollution profile shaped by vehicle traffic and localized heating/cooling demands. The relatively open landscape surrounding Westchester allows for some degree of pollutant dispersal, but the prevailing wind patterns and regional weather systems significantly dictate air quality conditions.

Westchester’s air quality experiences a distinct seasonal cycle driven by meteorological factors. Spring, while bringing relief from winter’s cold, often sees elevated pollen levels impacting respiratory health, though not directly related to particulate matter. Summer months are generally characterized by moderate air quality, though periods of heat and stagnant air can lead to ozone formation, particularly during sunny afternoons. The lack of significant rainfall during these periods exacerbates this issue. Autumn typically offers the most favorable air quality, with cooler temperatures and more frequent precipitation helping to cleanse the atmosphere. However, leaf burning, a practice still observed in some areas, can temporarily degrade local air quality. Winter presents the most significant air quality challenges. Cold temperatures combined with frequent temperature inversions trap pollutants near the ground, leading to increased concentrations of particulate matter and other emissions. These inversions, common during December and January, prevent vertical mixing, essentially creating a lid on the atmosphere. Fog, frequently occurring during winter mornings, further concentrates pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor exertion during these periods. While spring and fall offer opportunities for outdoor activities, awareness of pollen counts and occasional localized pollution events is advisable. The urban heat island effect, though less pronounced than in Chicago itself, can still contribute to localized ozone formation during summer evenings.