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Nāsriganj, a small city nestled within the broader plains of Bihar, India, occupies a geographically significant position at coordinates 25.0514°N, 84.3284°E. The terrain is predominantly flat alluvial land, characteristic of the Gangetic Plain, with an elevation hovering around 75 meters above sea level. This low-lying landscape contributes to limited natural dispersion of pollutants. The city is situated within a predominantly agricultural zone, heavily reliant on farming practices, particularly rice and wheat cultivation. While not directly adjacent to a major river, Nāsriganj is influenced by the regional hydrological network connected to the Ganges, impacting local humidity and potential for stagnant air masses. The urban-rural gradient is relatively sharp; the city itself is compact, quickly transitioning to surrounding agricultural fields and smaller villages. This proximity to agricultural land introduces seasonal burning of crop residue as a significant localised emission source. Industrial activity is limited within Nāsriganj itself, but regional industrial belts further afield contribute to background pollution levels transported by prevailing winds. The city’s location, coupled with its flat topography, creates conditions conducive to pollutant accumulation, particularly during periods of low wind speed and temperature inversions. Understanding these geographical factors is crucial for addressing Nāsriganj’s air quality challenges.

Nāsriganj experiences a distinct seasonal air quality pattern dictated by the monsoon and post-monsoon periods. The summer months (April-June) bring consistently high temperatures and low humidity, often accompanied by dust storms originating from the arid regions to the west. These storms significantly elevate particulate matter concentrations, making outdoor activity unpleasant for all, and particularly dangerous for those with respiratory conditions. The arrival of the monsoon (July-September) initially offers a respite, with rainfall effectively washing away pollutants. However, increased humidity can also trap pollutants closer to the ground. Post-monsoon (October-November) is often the worst period for air quality. Cooler temperatures create temperature inversions, trapping pollutants emitted from agricultural burning – a common practice after the harvest – and domestic sources. Fog formation further exacerbates the problem, reducing visibility and increasing pollutant concentrations. Winter (December-February) sees relatively stable air masses and continued burning, maintaining elevated pollution levels. Sensitive groups – children, the elderly, and those with pre-existing respiratory or cardiovascular conditions – should limit outdoor exposure during October-February, and consider using air purifiers indoors. Avoiding peak hours for outdoor activity and monitoring local conditions are also advisable.