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Harihans, a small town nestled in the fertile plains of Bihar, India, occupies a geographically significant position within the Ganges River basin. Located at approximately 26.1457° N, 84.3476° E, the town’s terrain is predominantly flat, characteristic of the Indo-Gangetic Plain. The elevation is relatively low, contributing to a tendency for pollutants to accumulate, particularly during periods of atmospheric stability. Harihans sits within a predominantly rural landscape, surrounded by agricultural fields – primarily rice and wheat cultivation – which, while vital to the regional economy, can contribute to seasonal particulate matter through crop residue burning. The town’s proximity to the Ganges River, though providing a crucial water source, also influences local weather patterns and can, under certain conditions, trap pollutants. The urban–rural gradient around Harihans is gradual; the town itself exhibits a modest urban character with a mix of residential areas, small-scale commercial establishments, and limited industrial activity, primarily related to agricultural processing. The broader region is part of a larger industrial belt extending towards eastern Uttar Pradesh, though the direct impact on Harihans is currently less pronounced than in larger urban centres. The flat topography and prevailing wind patterns, often influenced by the monsoon system, play a crucial role in the dispersion (or lack thereof) of air pollutants, making the town vulnerable to localized air quality challenges. The surrounding landscape, largely agricultural, dictates seasonal pollution sources.

Harihans experiences a distinct seasonal cycle that significantly impacts air quality. The pre-monsoon season (March-May) typically witnesses the poorest air quality, driven by a combination of factors. Agricultural residue burning, a common practice after the harvest of winter crops, releases substantial amounts of particulate matter and other pollutants into the atmosphere. High temperatures and stagnant air conditions, often associated with temperature inversions, exacerbate the problem by trapping these pollutants near the ground. The monsoon season (June-September) brings relief, as increased rainfall and stronger winds naturally cleanse the air. However, heavy rainfall can also lead to waterlogging and the release of methane from decomposing organic matter, contributing to localized pollution. The post-monsoon season (October-November) sees a gradual return to drier conditions, and unfortunately, a resurgence of agricultural burning, creating another peak in pollution levels. Winter months (December-February) are generally cooler, but fog formation is frequent, particularly in the early morning. This fog traps pollutants, reducing visibility and further degrading air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the pre-monsoon and post-monsoon seasons, limiting outdoor activity during peak pollution periods. Maintaining indoor air quality through ventilation and air purifiers is also advisable during these times. The monsoon offers a window of improved air quality, making it a preferable time for outdoor activities.