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Darjeeling, nestled in the Eastern Himalayas of West Bengal, India, occupies a uniquely challenging geographic position that profoundly influences its air quality. Situated at an elevation ranging from 1,370 to 3,280 meters (4,500 to 10,760 feet), the city’s topography is characterized by steep slopes and deep valleys, creating a complex interplay of air circulation patterns. The surrounding landscape is dominated by dense subtropical forests, tea plantations, and agricultural terraces, contributing both to natural air purification and potential sources of localized pollution. Darjeeling’s location on the southern slopes of the Himalayas means it’s sheltered from the harshest northerly winds, but also susceptible to air masses originating from the Indo-Gangetic Plain. This proximity to the Gangetic Plain, a region with significant industrial and agricultural activity, exposes Darjeeling to transboundary pollution. The Teesta River flows nearby, offering some degree of humidity, but its impact on air quality is secondary to the region’s elevation and prevailing winds. The urban–rural gradient is sharp; Darjeeling itself is a relatively small city, but it’s surrounded by numerous smaller villages and tea estates, each contributing to the overall regional air quality profile. The valley setting often traps pollutants, particularly during periods of low wind speed, exacerbating local air quality issues. The steep terrain also limits the dispersal of emissions from vehicles and small-scale industries within the city.

Darjeeling’s air quality exhibits a distinct seasonal pattern dictated by the region’s monsoon climate and Himalayan weather systems. The monsoon season, typically from June to September, brings heavy rainfall and strong winds, generally leading to improved air quality as pollutants are washed away and dispersed. However, increased biomass burning associated with agricultural practices during this period can temporarily elevate particulate matter levels. The pre-monsoon months (March-May) often experience a build-up of pollutants due to stagnant air and rising temperatures. Temperature inversions, common during these months, trap cooler air in the valleys, preventing the vertical mixing of pollutants and leading to poorer air quality. The winter months (November-February) are characterized by cold, calm conditions and frequent fog, which significantly reduces visibility and concentrates pollutants near ground level. This period often sees the highest levels of particulate matter, particularly fine particles. The dry winds from the north can also carry pollutants from the Indo-Gangetic Plain, further degrading air quality. Outdoor activities are generally best enjoyed during the monsoon months, although caution should be exercised regarding biomass burning. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor exposure during the winter and pre-monsoon seasons, especially during periods of dense fog. Maintaining indoor air quality through ventilation and air purifiers is also advisable during these times.