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Hashtpar, nestled in the Gilan province of northern Iran (37.7975° N, 48.9042° E), occupies a geographically significant position within the Caspian Hyrcanian mixed forests ecoregion. The city’s terrain is characterized by gently sloping hills and valleys, typical of the southern slopes of the Alborz Mountains, which provide a natural barrier to the north. This proximity to the mountains influences local weather patterns and contributes to the city’s microclimate. Hashtpar sits within a predominantly rural landscape, transitioning from agricultural fields – primarily rice paddies and orchards – to denser forest cover as one moves northward. The Caspian Sea, approximately 30 kilometers to the north, exerts a considerable influence, moderating temperatures and contributing to high humidity levels throughout the year. The surrounding landscape is a mosaic of cultivated land, scattered villages, and remnants of the ancient Hyrcanian forest, a biodiversity hotspot. While Hashtpar itself is a relatively small urban center, it lies within a broader agricultural belt, and the potential for agricultural emissions, particularly from fertilizer use and seasonal burning of crop residues, impacts local air quality. The urban–rural gradient is gradual, with agricultural activities interwoven within the city’s periphery. The elevation, averaging around 350 meters above sea level, further influences air circulation patterns, sometimes leading to localized stagnation and pollutant accumulation, especially during periods of calm weather. The city’s location within a humid subtropical climate zone means that rainfall is relatively consistent throughout the year, which can help to cleanse the air, but also contributes to fog formation, trapping pollutants.

Hashtpar’s air quality experiences a distinct seasonal cycle heavily influenced by its climate and surrounding environment. The wet season, spanning from autumn through spring, generally sees improved air quality due to frequent rainfall that naturally washes away particulate matter. However, autumn (October-November) can present challenges. Following the harvest season, agricultural burning, a traditional practice for clearing fields, releases significant amounts of smoke and particulate matter, creating localized air quality concerns. Winter (December-February) often brings periods of temperature inversion, where a layer of warm air traps cooler air near the ground, preventing pollutants from dispersing. This, combined with reduced wind speeds and increased residential heating (often using biomass fuels), can lead to stagnant air and elevated pollutant concentrations. Spring (March-May) brings a gradual improvement as temperatures rise and winds increase, dispersing pollutants. Summer (June-September) is typically the cleanest period, with higher temperatures promoting atmospheric mixing and frequent breezes from the Caspian Sea. Fog, common during the cooler months, can exacerbate air quality issues by trapping pollutants close to the ground. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during autumn and winter, particularly on days with limited wind and prevalent fog. Limiting outdoor exertion and avoiding areas with visible smoke are advisable. Public health advisories regarding agricultural burning are crucial during the post-harvest period to minimize exposure.