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Pekin, Illinois, situated at coordinates 40.5678° N, 89.6251° W, occupies a strategic, yet potentially vulnerable, position within the heartland of the United States. The city rests on relatively flat terrain characteristic of the Illinois River Valley, a landscape sculpted by glacial activity during the last ice age. This flatness contributes to limited natural air dispersion. The Illinois River itself, a major waterway, flows nearby, influencing local humidity and occasionally trapping pollutants during temperature inversions. Pekin’s location within Tazewell County places it within a predominantly agricultural region, dominated by corn and soybean farming. While this provides open space, agricultural practices contribute to particulate matter (PM) from tilling and harvesting, and ammonia emissions from fertilizer use. To the east lies a more densely populated corridor towards Bloomington-Normal, and westward the landscape transitions to more rural farmland. Historically, Pekin benefitted from river transport and industrial development, though much of that has shifted. The urban-rural gradient is relatively sharp, with surrounding farmland directly abutting the city limits. This proximity means pollutants generated within Pekin can quickly impact the surrounding agricultural areas, and vice versa, creating a complex regional air quality dynamic. The lack of significant topographical features hinders natural ventilation, exacerbating pollution episodes.

Pekin’s air quality follows a distinct seasonal pattern. Winter months, particularly December through February, often see the poorest air quality. Cold temperatures encourage increased residential heating with fossil fuels, leading to higher levels of particulate matter and sulfur dioxide. Temperature inversions are common during these months, trapping pollutants near the ground. Spring brings a temporary improvement as temperatures rise and precipitation increases, washing away some accumulated pollutants. However, agricultural activities begin, introducing dust and ammonia into the air. Summer generally offers the best air quality, with prevailing winds aiding dispersion and higher temperatures promoting pollutant breakdown. However, ozone formation can become a concern on hot, sunny days, particularly downwind of urban areas. Autumn sees a return to poorer conditions as heating demand increases and agricultural harvesting continues. October and November are often marked by stagnant air masses. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter and autumn. Monitoring local forecasts and avoiding peak pollution times is crucial. Periods of high humidity can also exacerbate respiratory issues. The relatively flat terrain limits natural air circulation, making Pekin susceptible to prolonged pollution events.