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Karahia, nestled in the state of Bihar, India, occupies a geographically significant position within the fertile Gangetic plains. Located at approximately 26.4054° N, 86.1490° E, the city’s terrain is predominantly flat, characteristic of the Indo-Gangetic Plain, with an elevation of roughly 62 meters above sea level. This low-lying topography, while conducive to agriculture, presents challenges regarding air quality dispersion. Karahia sits within a region heavily reliant on agriculture, particularly rice and maize cultivation, contributing to seasonal biomass burning and associated particulate matter. To the north and west, the landscape gradually transitions into more undulating terrain, though still largely agricultural. The proximity to the Ganges River, though not immediately adjacent, influences regional weather patterns and humidity levels, which can impact pollutant behaviour. The city’s urban character is that of a small, developing town, with a gradual urban–rural gradient extending outwards. While Karahia itself lacks major heavy industries, it’s situated within a broader industrial belt that stretches along the Ganges, with smaller manufacturing units and processing facilities contributing to localized pollution. The prevailing winds, often influenced by regional weather systems, can transport pollutants from these industrial areas, impacting Karahia’s air quality. The flat landscape and limited natural barriers exacerbate the issue, hindering the natural dispersal of pollutants and leading to their accumulation, especially during periods of stagnant air. The surrounding landscape, dominated by agricultural fields and scattered rural settlements, further complicates the air quality picture, introducing agricultural emissions into the mix.

Karahia’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 worst air quality, driven by a combination of factors. Agricultural residue burning, a common practice after the harvest of winter crops, releases significant quantities of particulate matter and gases. High temperatures and low wind speeds during this period create atmospheric stability, fostering temperature inversions that trap pollutants near the ground. The dry air also exacerbates respiratory irritation. The monsoon season (June-September) brings relief, with increased rainfall and stronger winds effectively flushing out pollutants. Humidity levels rise, which can temporarily alleviate some respiratory discomfort. However, heavy rainfall can also lead to waterlogging and the release of methane from decomposing organic matter, contributing to ground-level ozone formation. The post-monsoon season (October-November) sees a return to drier conditions and a resurgence of agricultural burning, mirroring the pre-monsoon pattern. Winter months (December-February) are generally cooler, but fog formation is common, particularly in the early morning. This fog traps pollutants, leading to periods of reduced visibility and elevated particulate matter concentrations. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit outdoor activity during the pre-monsoon and post-monsoon seasons, especially on days with visible haze or fog. Staying indoors with air purifiers and wearing N95 masks can offer some protection. Hydration and avoiding strenuous activity are also recommended.