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Diphu, nestled in the Karbi Anglong district of Assam, India, occupies a geographically significant position within the northeastern Himalayan foothills. Located at approximately 25.83°N, 93.43°E and an elevation of around 230 meters (750 feet) above sea level, the city’s terrain is characterized by undulating hills and valleys, typical of the region's geomorphology. The surrounding landscape is predominantly forested, with dense tropical moist deciduous forests dominating the area, contributing to a generally humid climate. The Kopili River flows nearby, influencing local microclimates and providing a source of water. Diphu’s urban character is relatively nascent, exhibiting a gradual urban–rural gradient as it expands. While the core area displays a concentrated settlement pattern, the outskirts blend seamlessly into the agricultural landscape, where rice cultivation and horticulture are prevalent. This proximity to agricultural zones, while supporting livelihoods, can contribute to seasonal particulate matter from agricultural burning, particularly during post-harvest periods. Further afield, the broader Assam region hosts pockets of industrial activity, primarily related to tea processing and timber industries, which can occasionally impact Diphu’s air quality through transported pollutants. The hilly topography can also lead to localized air stagnation, especially during periods of low wind speed, exacerbating the effects of any emissions. The region's monsoon climate significantly influences drainage patterns and humidity levels, further impacting atmospheric conditions.

Diphu’s air quality experiences a distinct seasonal cycle dictated by the region’s monsoon climate. The monsoon season, typically spanning June to September, brings heavy rainfall and strong winds, effectively flushing out pollutants and generally improving air quality. This period is often the most favourable for outdoor activities. Conversely, the pre-monsoon months (March-May) often see a rise in particulate matter concentrations. Agricultural burning following the winter harvest contributes significantly to this, alongside increased dust from road construction and general activity. Temperature inversions, common during these months, trap pollutants near the ground, worsening conditions. The post-monsoon season (October-November) presents a transitional period. While rainfall decreases, the lingering humidity and cooler temperatures can lead to fog formation, particularly in the mornings. This fog traps pollutants, creating periods of reduced visibility and potentially impacting air quality. Winter (December-February) is generally drier, with lower humidity, but can still experience periods of stagnant air and localized pollution, especially when combined with fog. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the pre-monsoon and post-monsoon seasons, limiting prolonged outdoor exposure during periods of reduced visibility or noticeable air irritation. Maintaining indoor air quality through ventilation and air purification can also be beneficial during these times. The strong winds associated with the monsoon provide a natural cleansing effect, making it the most suitable time for outdoor recreation.