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Nestled in the Palpa District of Nepal, Gulariyā (28.2056° N, 81.3472° E) occupies a strategically important position within the Terai plains, a low-lying, fertile region bordering India. The city’s elevation, around 285 meters (935 feet) above sea level, contributes to its warm, subtropical climate and places it within a zone susceptible to ground-level ozone formation. Gulariyā’s landscape is characterized by expansive agricultural fields, primarily dedicated to rice and wheat cultivation, interspersed with pockets of sal forests and riverine vegetation along the Tinau River, which flows nearby. This river acts as a crucial water source and influences local humidity. The urban fabric of Gulariyā is relatively compact, exhibiting a gradual urban-rural gradient as one moves outwards. While the core area features denser residential and commercial development, the periphery transitions seamlessly into agricultural land and smaller settlements. The city’s proximity to the Siddhartha Highway, a major transportation artery, introduces vehicular emissions as a significant factor. Furthermore, the Terai’s location downwind of the Himalayas means it frequently receives pollutants transported from the higher elevations, particularly during periods of stagnant air. The surrounding landscape, while largely agricultural, also includes small-scale brick kilns and agricultural processing units, which can contribute localized air pollution episodes. The flat terrain limits natural air dispersion, exacerbating the impact of these sources.

Gulariyā’s air quality follows a distinct seasonal pattern dictated by the monsoon and its associated meteorological conditions. The pre-monsoon months (March-May) typically experience the poorest air quality. Rising temperatures and intense solar radiation promote the formation of ground-level ozone, a respiratory irritant. Calm wind conditions during this period trap pollutants near the surface, leading to elevated concentrations. Dust storms, common during this time, further degrade air quality. The monsoon season (June-September) brings a welcome respite. Frequent rainfall effectively ‘washes’ pollutants from the atmosphere, and increased wind speeds facilitate dispersion. However, monsoon-related activities like agricultural burning, though regulated, can still contribute to localized smoke events. Post-monsoon (October-November) sees a gradual return to drier conditions, and with it, a renewed risk of ozone formation, though generally less severe than in the pre-monsoon period. Winter (December-February) is characterized by cooler temperatures and frequent fog, particularly in the early morning hours. While temperatures are lower, the fog traps pollutants, creating periods of reduced visibility and potentially impacting respiratory health. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit prolonged outdoor exposure during the pre-monsoon and winter months, especially during periods of fog or stagnant air. Maintaining indoor air quality through ventilation and air purification can also be beneficial during these times.