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Semra, a small town in the eastern Indian state of Bihar, sits at coordinates 26.6523°N, 85.0872°E. Its geography is characteristic of the Indo-Gangetic Plain – a flat, fertile alluvial landscape. The town’s elevation is relatively low, contributing to limited atmospheric dispersion of pollutants. Semra is situated within the Muzaffarpur district, a region heavily reliant on agriculture, particularly rice and sugarcane cultivation. This agricultural activity, while vital to the local economy, introduces particulate matter from crop residue burning and fertilizer use. The Burhi Gandak river flows nearby, influencing local humidity and potentially trapping pollutants during temperature inversions. The urban-rural gradient is pronounced; Semra itself is a relatively small settlement, but is surrounded by numerous villages engaged in farming. Industrial activity is limited within Semra itself, but the broader Muzaffarpur region has some small-scale brick kilns and food processing units, contributing to localised emissions. The flat terrain and lack of significant natural barriers mean that pollutants can accumulate easily, especially during periods of stagnant air. The town’s position within the Indo-Gangetic Plain makes it susceptible to long-range transport of pollutants from larger urban centres to the west and northwest. This combination of factors creates a challenging environment for maintaining good air quality.

Semra’s air quality follows a distinct seasonal pattern. The post-monsoon period, from October to November, often sees a deterioration in air quality due to the burning of crop residue after the harvest, coupled with cooler temperatures and increased temperature inversions that trap pollutants near the ground. This is generally the most challenging time for respiratory health. December and January bring colder, drier conditions, exacerbating particulate matter concentrations as dust remains suspended for longer. The pre-monsoon months, March to May, witness rising temperatures and dust storms, further degrading air quality. The monsoon season, from June to September, provides a temporary respite. Heavy rainfall effectively washes away pollutants, and increased humidity causes particles to settle. However, increased cloud cover can also contribute to temperature inversions. Outdoor activity is generally most favourable during the monsoon months, though mould growth can pose a separate health concern. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit outdoor exposure during the post-monsoon and winter months. Avoiding peak hours near agricultural areas during crop burning is also advisable. Monitoring local weather patterns and heeding health advisories are crucial for protecting respiratory health.