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Khorramābād, nestled within the Māzandarān Province of Iran at coordinates 36.7822° N, 50.8714° E, presents a unique geographic setting influencing its air quality. The city sits within the Alborz mountain range foothills, a region characterised by a relatively low elevation, approximately 128 meters above sea level. This positioning within a valley contributes to potential air stagnation, trapping pollutants. The surrounding landscape is dominated by agricultural lands, particularly rice paddies and orchards, common to the Caspian Sea coastal plain. While not directly on the Caspian Sea coastline, Khorramābād benefits from the moderating influence of the sea’s proximity, experiencing higher humidity levels. The urban-rural gradient is relatively sharp, with agricultural activity immediately bordering the city limits. Industrial activity is present, though not concentrated in massive belts, consisting primarily of food processing related to the agricultural output and smaller-scale manufacturing. Dust from agricultural practices, combined with emissions from local transport and industry, are key factors impacting air quality. The terrain’s limited capacity for atmospheric dispersion, coupled with seasonal weather patterns, creates conditions conducive to pollutant build-up, particularly during calmer periods. Understanding this interplay between geography and human activity is crucial for effective air quality management in Khorramābād.

Khorramābād’s air quality follows a distinct seasonal pattern, largely dictated by meteorological conditions. Spring (March-May) sees increasing agricultural activity, leading to a rise in particulate matter from tilling and harvesting, alongside pollen. Summer (June-August) brings higher temperatures and generally stronger winds, which can temporarily disperse pollutants, but also exacerbate ozone formation due to increased photochemical reactions. However, stable atmospheric conditions can still trap pollutants in the valley. Autumn (September-November) is often the most challenging period. Decreasing temperatures create temperature inversions, trapping cooler air – and pollutants – near the ground. Reduced wind speeds further hinder dispersion. This is when emissions from heating sources begin to increase. Winter (December-February) sees continued temperature inversions and increased reliance on fossil fuels for heating, contributing to higher concentrations of sulfur dioxide and particulate matter. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during autumn and winter. Spring can also pose challenges due to pollen. Months to favour for outdoor activity are generally June and July, but even then, monitoring conditions is advisable. Fog, common in the cooler months, can also trap pollutants, reducing visibility and worsening air quality.