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Salmās, nestled in the northwestern corner of Iran’s Āz̄arbāyjān-e Gharbī province, occupies a unique geographic position. Situated at coordinates 38.2028° N, 44.7669° E, the city lies within a valley surrounded by the Zagros Mountains, creating a basin-like topography. This terrain significantly influences air quality, as the mountains can trap pollutants, hindering their dispersion. The elevation, averaging around 1,450 meters (4,757 feet), contributes to cooler temperatures and potential for temperature inversions, exacerbating pollution events. Salmās is relatively distant from major industrial centres, but benefits from fertile agricultural lands surrounding the city, primarily dedicated to wheat, barley, and fruit orchards. These agricultural activities, while vital to the local economy, contribute to particulate matter through dust from tilling and potential pesticide use. The urban-rural gradient is relatively sharp, with agricultural lands immediately bordering the city limits. The proximity to the Turkish border and the Urmia Lake (though some distance away, its shrinking size impacts regional dust storms) also plays a role in regional air circulation patterns. The city’s location within a semi-arid climate further influences dust and particulate matter levels, particularly during drier periods. Understanding these geographical factors is crucial for addressing Salmās’s air quality challenges.

Salmās experiences a distinct seasonal air quality pattern dictated by its climate and local activities. Spring (March-May) sees a gradual improvement in air quality as snowmelt washes away accumulated pollutants, but agricultural burning for land preparation can temporarily elevate particulate matter. Summers (June-August) are generally drier, with increased dust from surrounding agricultural lands and potential for long-range transport of dust from regional sources. Temperature inversions, common during calm summer nights, trap pollutants near the ground. Autumn (September-November) often brings the most stable air quality, with cooler temperatures and increased precipitation helping to cleanse the atmosphere. However, the start of the heating season introduces emissions from residential fuel burning. Winters (December-February) are characterized by cold temperatures and frequent temperature inversions, leading to the highest pollution levels. Snowfall can temporarily improve conditions, but also traps pollutants when it melts. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during winter months and periods of calm weather. Months to favour for outdoor activity are generally September and October. Fog, common in winter, can also exacerbate particulate matter concentrations, reducing visibility and impacting respiratory health.