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Hariharpāra, a small urban centre in West Bengal, India, occupies a geographically significant position within the sprawling Kolkata Metropolitan Area. Located at approximately 24.0468° N, 88.4244° E, the city’s terrain is predominantly flat, characteristic of the Gangetic plain. Its elevation is relatively low, contributing to atmospheric stability and potential for pollutant accumulation. Hariharpāra sits on the fringes of Kolkata, experiencing a gradual urban–rural gradient as one moves outwards. The surrounding landscape is a mix of agricultural fields – primarily rice paddies and vegetable farms – and smaller settlements, typical of the fertile delta region. The Hooghly River, a major distributary of the Ganges, flows nearby, influencing local humidity and temperature patterns. While not directly adjacent, the river’s presence impacts regional weather systems. The city’s proximity to Kolkata’s industrial belts, particularly those concentrated in the northern and eastern sectors of the metropolitan area, is a crucial factor affecting air quality. These industrial zones release various pollutants, which can be transported to Hariharpāra via prevailing winds. The urban sprawl of Kolkata itself contributes significantly to the overall pollution load, with vehicular emissions and construction activities impacting air quality across the wider region. The flat topography and relatively low wind speeds, common to the Bengal delta, can exacerbate the persistence of pollutants, especially during periods of atmospheric stability. The surrounding agricultural practices, while vital for the regional economy, can also contribute to air pollution through the burning of crop residue, particularly after the harvest season.

Hariharpāra’s air quality follows a distinct seasonal pattern dictated by the region’s monsoonal climate. The summer months (March to May) are typically characterized by high temperatures and low relative humidity, leading to stagnant air conditions and increased pollutant concentrations. The intense heat promotes the formation of photochemical smog, exacerbated by emissions from vehicles and industries. Dust storms, originating from the arid regions of northwest India, frequently impact air quality during this period, further degrading visibility and respiratory health. The monsoon season (June to September) brings a welcome respite, with increased rainfall and stronger winds that effectively flush out pollutants. However, heavy rainfall can also lead to increased humidity and the release of biogenic volatile organic compounds (BVOCs), which can contribute to ozone formation under certain conditions. The post-monsoon season (October to November) often sees a return to poorer air quality as wind speeds decrease and temperatures begin to drop, creating conditions conducive to temperature inversions – a phenomenon where a layer of warm air traps cooler air and pollutants near the ground. Winter (December to February) is generally the most challenging period, with frequent fog and low temperatures further trapping pollutants. The combination of reduced wind speeds, temperature inversions, and fog creates a ‘brown haze’ that significantly impacts air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor activity during these periods, particularly during early morning hours when fog is most prevalent. Maintaining indoor air quality through ventilation and air purification can also be beneficial.