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Rasiāri, a small city nestled within the plains of Bihar, India, occupies a geographically significant position at coordinates 26.0464°N, 86.3471°E. The terrain is characteristically flat, typical of the Indo-Gangetic Plain, with a low elevation contributing to limited natural air dispersion. The city’s location is deeply interwoven with the agricultural landscape of Bihar, surrounded by intensely cultivated fields – primarily rice and wheat – which, while vital for the regional economy, contribute to seasonal biomass burning. Rasiāri isn’t directly adjacent to a major river, but lies within the broader watershed of the Ganges, influencing local humidity and potential for localised flooding during the monsoon. The urban-rural gradient is sharp; Rasiāri itself is a relatively small urban centre, quickly transitioning to rural agricultural land. While not a major industrial hub, the increasing presence of small-scale brick kilns and agro-processing units in the surrounding districts adds to the particulate matter load. The lack of significant topographical features – hills or valleys – hinders the flushing of pollutants, making Rasiāri susceptible to air stagnation, particularly during calmer weather conditions. This flat, agricultural setting, combined with emerging localised industry, defines the city’s air quality challenges.

Rasiāri 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 stagnant air, exacerbating dust and particulate matter from agricultural activities and unpaved roads. October-November, following the monsoon’s retreat, is often the worst period, coinciding with post-harvest crop residue burning – a major source of PM2.5. Shallow temperature inversions are common during these cooler months, trapping pollutants near ground level. The monsoon season (July-September) offers temporary relief, as rainfall effectively washes away pollutants and increased humidity suppresses dust. However, increased cloud cover can also contribute to localised smog formation. Winter (December-February) sees cooler temperatures and often foggy conditions, trapping pollutants and reducing visibility. For those with respiratory sensitivities, avoiding outdoor activity during October-November and early morning hours in winter is advisable. The monsoon, while bringing relief, can also increase mould spore counts. Monitoring local conditions and limiting strenuous activity on poor air quality days is crucial for all residents, particularly children and the elderly.