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Kāshān, situated in the arid heart of Iran's Eşfahān Province at coordinates 33.9825°N, 51.4325°E, occupies a strategic position on the historic Silk Road between the Dasht-e Kavir desert to the north and the Karkas Mountains to the south. Nestled at approximately 1,000 meters above sea level in a semi-enclosed basin, the city's geography creates a natural trap for air pollutants. The surrounding landscape features desert plains to the east and rugged foothills to the west, with minimal vegetation to filter airborne particulates. Kāshān lies approximately 240 kilometers south of Tehran in Iran's central industrial belt, though it maintains a distinct character as a historic oasis city with traditional architecture and renowned rosewater production. The urban-rural gradient shows compact historic quarters transitioning to modern suburbs, with agricultural zones cultivating pistachios, pomegranates, and roses in the surrounding fertile strips fed by qanat systems. No major bodies of water moderate the climate, contributing to extreme temperature variations. This basin topography, combined with the city's position downwind of regional industrial activities and its own urban emissions from transportation and heating, creates persistent air quality challenges, particularly during temperature inversions that trap pollutants in the valley.

Kāshān's air quality follows distinct seasonal patterns shaped by its continental desert climate. Winter (December-February) brings the worst pollution as cold, stagnant air settles in the basin, creating frequent temperature inversions that trap emissions from residential heating (often using fossil fuels) and limited vehicle dispersion. Sensitive groups should minimize outdoor activity during these months, especially on calm, foggy mornings. Spring (March-May) sees gradual improvement with increasing winds that disperse pollutants, though late spring dust storms from the surrounding deserts can temporarily spike particulate levels. Summer (June-August) offers the cleanest air despite intense heat, as strong thermal convection and occasional northerly winds ventilate the basin, though ozone may become a concern on hot, sunny days. Autumn (September-November) begins with relatively good air quality that deteriorates as temperatures drop and atmospheric stability increases, with November often marking the transition to winter pollution conditions. The peak pollution typically occurs in December-January, while May-September generally provides the most favorable conditions for outdoor activities. Visitors with respiratory conditions should plan trips for spring or early autumn, avoid strenuous exercise during winter inversions, and monitor local air quality reports year-round.