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Kīāshahr, nestled in the Gilan province of northern Iran, occupies a geographically significant position within the broader Caspian Hyrcanian mixed forests ecoregion. Located at approximately 37.4214° N, 49.9408° E, the city’s terrain is characterized by rolling hills and valleys, sloping gently towards the Caspian Sea, roughly 20 kilometers to the north. This proximity to the sea exerts a considerable influence on the local climate and, consequently, air quality. The surrounding landscape is dominated by lush, temperate forests, interspersed with agricultural lands – primarily rice paddies and orchards – contributing to a distinct urban-rural gradient. Kīāshahr itself is a relatively small city, exhibiting a compact urban footprint with a noticeable transition to rural agricultural areas within a short distance. The Hyrcanian forest, a remnant of ancient forests stretching from the Caucasus to northern Iran, acts as a natural air filter, absorbing pollutants and moderating temperatures. However, the presence of smaller-scale industrial activity, including brick kilns and agricultural processing facilities, and the transportation of goods along regional roads, introduces localized sources of air pollution. The elevation, averaging around 350 meters above sea level, can contribute to temperature inversions during certain periods, trapping pollutants near the ground. The city’s location within a humid subtropical climate zone, with abundant rainfall, generally aids in pollutant dispersion, but specific meteorological conditions can override this effect.

Kīāshahr’s air quality experiences a distinct seasonal cycle heavily influenced by its humid subtropical climate and proximity to the Caspian Sea. During the spring (March-May), increased agricultural activity, including fertilizer application and burning of crop residues, contributes to elevated levels of particulate matter and ammonia. The warming temperatures also encourage the release of volatile organic compounds (VOCs) from vegetation. Summer (June-August) typically sees improved air quality due to stronger prevailing winds from the Caspian Sea, which effectively disperse pollutants. However, periods of intense heat can lead to stagnant air and ozone formation. Autumn (September-November) marks a transition period, with decreasing temperatures and calmer winds, often resulting in a build-up of pollutants, particularly in the mornings when fog is common. This fog traps emissions, exacerbating local air quality issues. Winter (December-February) is often the most challenging period. Cold, stable air masses frequently lead to temperature inversions, preventing vertical mixing and trapping pollutants close to the ground. The increased use of solid fuels for heating in homes and smaller businesses further compounds the problem. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor activity during these periods, especially on days with visible haze or fog. Maintaining indoor air quality through ventilation and air purification can also be beneficial. Public health advisories are often issued during periods of poor air quality, recommending reduced physical exertion and avoiding areas with high traffic density.