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Kalārdasht, nestled in the lush Māzandarān province of northern Iran, occupies a geographically significant position within the Alborz mountain range. Located at approximately 36.5056° N, 51.1589° E, and with an elevation of around 1,350 meters (4,430 feet) above sea level, the city benefits from, and is simultaneously influenced by, its mountainous terrain. The surrounding landscape is dominated by dense forests of Caspian hyrcanian, a unique temperate rainforest ecosystem, transitioning outwards to agricultural lands and eventually the coastal plains of the Caspian Sea, roughly 50 kilometers to the north. This urban–rural gradient presents a complex interplay of factors impacting air quality. The city’s proximity to the Caspian Sea introduces a maritime influence, increasing humidity and potentially trapping pollutants under certain meteorological conditions. While Kalārdasht itself is a relatively small town with a population of around 13,401, it sits within a region experiencing increasing agricultural activity, particularly rice cultivation, which can contribute to ammonia emissions and methane release. Further afield, industrial zones concentrated along the southern coast of the Caspian Sea, though not immediately adjacent, can contribute to regional pollution transport. The topography, with its steep slopes and valleys, can exacerbate air pollution by hindering dispersion, particularly during periods of low wind speed and temperature inversions, common in the autumn and winter months. The prevailing winds, generally flowing from the Caspian Sea inland, also play a crucial role in the distribution of pollutants.

Kalārdasht’s air quality experiences a distinct seasonal cycle heavily influenced by regional weather patterns. The wet season, spanning autumn and winter (September to March), typically sees the poorest air quality. Persistent fog, a common occurrence due to the high humidity from the Caspian Sea and cooler temperatures, traps pollutants close to the ground, leading to stagnant air conditions. Temperature inversions, where a layer of warm air sits above cooler air, further inhibits vertical mixing, exacerbating this effect. Agricultural activities, including post-harvest burning of rice straw, contribute significantly to particulate matter during this period. Spring (April to June) brings a gradual improvement as temperatures rise, and winds become more frequent, aiding in pollutant dispersal. However, dust storms originating from the central Iranian deserts can occasionally impact air quality, though less frequently than in more southerly regions. Summer (July to August) generally offers the best air quality, with strong winds and higher temperatures promoting good ventilation. However, intense heat can lead to the formation of ground-level ozone, a secondary pollutant. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the autumn and winter months, limiting outdoor activity during periods of heavy fog or stagnant air. During the summer, avoiding strenuous activity during peak heat hours is advisable. The agricultural cycle dictates periods of heightened concern, particularly after the rice harvest when burning practices are prevalent. Maintaining indoor air quality through proper ventilation and air filtration is crucial throughout the year.