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Bhirāha, nestled in the fertile plains of Bihar, India, occupies a geographically significant position within the Gangetic Basin. Located at approximately 25.7978° N, 86.0736° E, the city’s terrain is predominantly flat, characteristic of the Indo-Gangetic Plain, with an elevation of around 55 meters above sea level. This low-lying topography, while conducive to agriculture, presents challenges for air quality dispersion. Bhirāha is surrounded by a landscape dominated by agricultural fields – primarily rice and maize cultivation – which, during certain periods, contribute to particulate matter through crop residue burning. The city’s proximity to the Son River, though providing a vital water source, also influences local humidity and temperature, impacting atmospheric stability and pollutant behaviour. The urban–rural gradient around Bhirāha is relatively gradual, with smaller villages and agricultural hamlets blending seamlessly into the urban fabric. While Bhirāha itself is a relatively small town, it sits within a broader regional network connected to larger urban centres like Patna, which can influence air quality through long-range transport of pollutants. The lack of significant natural barriers, such as hills or mountains, further exacerbates the issue, allowing pollutants to spread easily across the flat landscape. Industrial activity in the surrounding districts, though not directly within Bhirāha, can contribute to regional air pollution episodes, impacting the city’s air quality. The flat terrain and prevailing wind patterns often trap pollutants, particularly during periods of low wind speed and temperature inversions.

Bhirāha’s air quality experiences a distinct seasonal cycle heavily influenced by the monsoon and agricultural practices. The pre-monsoon season (March-May) typically witnesses the poorest air quality. This period coincides with the harvesting of winter crops, leading to widespread crop residue burning, a significant source of particulate matter and noxious gases. Dry, hot conditions and stagnant air masses further worsen the situation, trapping pollutants close to the ground. The monsoon season (June-September) brings relief, with increased rainfall and stronger winds dispersing pollutants. However, humidity levels rise considerably. Post-monsoon (October-November) sees a return to drier conditions, and unfortunately, another period of crop residue burning, though often less intense than in the pre-monsoon season. Winter months (December-February) are generally cooler, but fog formation is common, particularly in the early morning. This fog traps pollutants, creating localized episodes of poor air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor activity during the pre-monsoon and post-monsoon seasons, especially on days with visible smoke or fog. During the monsoon, while overall air quality improves, high humidity can still exacerbate respiratory issues for some. Maintaining indoor air quality through ventilation and air purifiers is advisable throughout the year, with particular emphasis during periods of elevated pollution. The combination of agricultural practices and meteorological conditions creates a challenging environment for maintaining clean air in Bhirāha.