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Karahrūd, nestled within Markazi Province, Iran, occupies a geographically significant position in the central Iranian plateau. Located at coordinates 34.0628° N, 49.6461° E, the city sits at an elevation of approximately 1,680 meters (5,512 feet) above sea level. This altitude contributes to a cooler, drier climate compared to lower-lying regions. The surrounding landscape is characterised by semi-arid mountains and valleys, part of the Alborz mountain range’s eastern extensions. Karahrūd isn’t directly adjacent to major bodies of water, though seasonal rivers and streams flow down from the mountains, providing limited irrigation. The urban-rural gradient is relatively sharp; the city itself is compact, with a population of around 29,721, quickly transitioning to agricultural lands dominated by wheat, barley, and fruit orchards. To the east and west lie more extensive agricultural zones. While Karahrūd isn’t a major industrial hub, smaller-scale industrial activity, including food processing and building materials production, exists on the city’s periphery. This, combined with domestic heating during colder months and dust storms originating from the arid regions to the south and east, significantly influences local air quality. The valley location can also trap pollutants, exacerbating air quality issues, particularly during temperature inversions.

Karahrūd experiences a distinct seasonal air quality pattern. Spring (March-May) brings a temporary improvement as increased rainfall washes away accumulated pollutants, though agricultural burning can briefly elevate particulate matter. Summers (June-August) are typically drier, with hot temperatures and stable atmospheric conditions. This can lead to the build-up of ozone and other secondary pollutants, particularly if regional dust storms occur. Autumn (September-November) often sees a deterioration in air quality as temperatures drop and domestic heating with fossil fuels increases. This period is frequently marked by temperature inversions, trapping pollutants close to the ground. Winter (December-February) is the most challenging season, with consistently cold temperatures and increased reliance on coal and wood for heating. This results in high concentrations of particulate matter (PM2.5 and PM10) and sulfur dioxide. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during November to February. Months like April and May, with cleaner air following the winter and before the summer heat, are generally more favourable. Wind patterns, predominantly from the west, can occasionally provide relief by dispersing pollutants, but these events are infrequent.