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Ahar, nestled in the northwestern Iranian province of Āz̄arbāyjān-e Sharqī, occupies a significant position within the East Azerbaijan region. The city is situated at an elevation of approximately 1,580 meters (5,184 feet) amidst the rugged terrain of the Alborz mountain range’s eastern extensions. This mountainous backdrop profoundly influences Ahar’s climate and, consequently, its air quality. The surrounding landscape is characterised by steep slopes, valleys, and limited flat land, impacting wind patterns and creating localized pockets where pollutants can accumulate. Ahar isn’t directly adjacent to major bodies of water, though smaller rivers and streams originating from the mountains traverse the area. The urban-rural gradient is quite sharp; the city centre transitions rapidly into agricultural lands, primarily dedicated to dry farming of wheat, barley, and fruits like apples and pears. While Ahar isn’t a major industrial hub, smaller-scale industries, including food processing and brick manufacturing, contribute to localised emissions. Dust from agricultural activities and unpaved roads, combined with the mountainous topography hindering dispersion, are key factors affecting baseline air quality. The city’s location within a valley can exacerbate pollution events, trapping emissions during periods of atmospheric stability. The prevailing winds, often channeled through the valleys, can also transport pollutants from surrounding areas.

Ahar experiences a continental climate with distinct seasons, each impacting air quality differently. Spring (March-May) sees increasing agricultural activity, leading to dust and particulate matter from field preparation. Melting snow from the mountains contributes to increased river flow but doesn’t significantly affect air pollution. Summers (June-August) are generally drier with higher temperatures, promoting atmospheric stability and trapping pollutants, particularly from vehicle emissions and local industries. August often experiences the poorest air quality. Autumn (September-November) brings a temporary improvement as rainfall washes away accumulated pollutants and agricultural activity slows. However, temperature inversions become more frequent, trapping cold air beneath warmer layers, exacerbating pollution in the valley. Winter (December-February) is characterised by cold temperatures and occasional snowfall. Heating with fossil fuels, particularly coal and wood in residential areas, becomes the dominant source of pollution, leading to elevated levels of particulate matter and sulfur dioxide. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during December and January. Months of May-June and September-October generally offer the most favourable air quality conditions for outdoor activities, though monitoring conditions remains crucial.