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Arak, situated in the Markazi Province of west-central Iran, occupies a strategic position within the Iranian plateau at an elevation of approximately 1,750 meters above sea level. This city lies in a basin surrounded by the Zagros Mountains to the west and the Karkas Mountains to the east, creating a topographical enclosure that significantly influences its air quality. The urban area is positioned near the Qara Chay River, though this seasonal watercourse provides minimal moderating effect on the local climate. Arak functions as a major industrial hub within Iran's central industrial belt, with its economy dominated by heavy manufacturing including the prominent Arak Aluminum Smelter, one of the largest in the Middle East. The city's location in this semi-arid valley creates a natural amphitheater effect where pollutants become trapped, particularly during temperature inversions. The urban-rural gradient shows dense industrial zones concentrated in the city's periphery, while agricultural lands of the Markazi plains surround the metropolitan area, contributing occasional agricultural dust. This geographical setting, combined with the city's industrial character and basin topography, creates persistent challenges for air dispersion, making Arak particularly vulnerable to pollutant accumulation even with moderate emissions.

Arak's air quality follows a distinct seasonal pattern shaped by its cold semi-arid climate and industrial emissions. During winter (November-January), pollution reaches its peak as temperature inversions trap vehicle exhaust, industrial emissions, and residential heating pollutants close to the ground, compounded by reduced atmospheric mixing and occasional fog. These months present the highest health risks, particularly for sensitive groups like children, elderly, and those with respiratory conditions who should limit outdoor exposure. Spring (March-May) brings gradual improvement as increased wind activity, sometimes carrying dust from surrounding plains, helps disperse pollutants, though dust storms can temporarily degrade air quality. Summer (June-August) sees moderate pollution levels despite industrial activity continuing, as stronger thermal convection and occasional breezes provide better vertical mixing, though extreme heat can exacerbate ozone formation. Autumn (September-October) marks a transitional period with generally acceptable air quality before winter conditions set in. For optimal outdoor activities, late spring through early autumn offers the most favorable conditions, while winter months require precautions like indoor air filtration and reduced strenuous activity outdoors, especially during morning hours when inversions are strongest.