Tonekābon, nestled within the Māzandarān Province of Iran, occupies a significant position along the southern coast of the Caspian Sea. Located at coordinates 36.8153°N, 50.8711°E, the city’s geography is profoundly shaped by the Alborz mountain range rising steeply to the south, creating a relatively narrow coastal plain. This terrain significantly influences air quality, acting as a barrier to air circulation and potentially trapping pollutants. Tonekābon’s elevation is relatively low, contributing to humidity and the potential for temperature inversions, especially during calmer weather. The Caspian Sea exerts a moderating influence on the climate, but also introduces moisture that can exacerbate pollution by forming fog and increasing particulate matter. Surrounding Tonekābon are extensive agricultural lands, particularly rice paddies and citrus groves, which contribute to seasonal biomass burning and ammonia emissions. The urban-rural gradient is fairly sharp, with agricultural activity dominating the immediate periphery. While not a major industrial hub itself, Tonekābon’s proximity to larger industrial areas further east along the Caspian coast means it can be affected by long-range transport of pollutants. The city’s location within a valley-like formation further restricts air dispersal, making it vulnerable to localised pollution build-up.

Tonekābon experiences a temperate climate with distinct seasonal variations impacting air quality. Spring (March-May) sees increasing agricultural activity, including field preparation and burning of crop residue, leading to elevated particulate matter and carbon monoxide levels. The melting snow from the Alborz mountains also contributes to increased river flow and potential localised humidity, trapping pollutants. Summers (June-August) are generally warmer and drier, with prevailing winds from the Caspian Sea offering some dispersal, but stagnant air masses can still occur, concentrating ozone and other secondary pollutants. Autumn (September-November) is often marked by increased fog and humidity, exacerbating particulate matter pollution as cooler temperatures lead to temperature inversions. This is a period of harvest and associated agricultural burning, further degrading air quality. Winters (December-February) are relatively mild due to the Caspian Sea’s influence, but temperature inversions are common, trapping pollutants from domestic heating sources – primarily wood and fossil fuels. Sensitive groups, including children, the elderly, and those with respiratory conditions, should limit outdoor activity during autumn and winter months. Spring can also pose risks due to agricultural emissions. Monitoring wind patterns and avoiding peak agricultural burning periods are advisable.