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Nestled in the Nalanda district of Bihar, Rajgir occupies a unique geographical position within the Gangetic Plain of South Asia, situated at coordinates 25.0300°N, 85.4200°E. This historic city lies approximately 100 kilometers southeast of Patna, Bihar's capital, and is enveloped by the Rajgir Hills, a range of low, rocky outcrops that form part of the ancient Vindhya mountain system. Rajgir's elevation varies between 60 to 100 meters above sea level, with its urban core nestled in a valley surrounded by five hills—Vaibhara, Vipula, Ratna, Udaya, and Sonagiri—creating a natural amphitheater that significantly influences its air quality. The city's proximity to the Falgu River, a seasonal tributary of the Ganges, adds to its hydrological context, though the river often runs dry outside the monsoon season. Rajgir's location within an agricultural belt dominated by rice and wheat cultivation contributes to seasonal biomass burning, while its status as a major Buddhist pilgrimage and tourism hub intensifies vehicle emissions. The urban-rural gradient is pronounced, with dense settlement in the valley giving way to rural villages and forested hillsides. This topography traps pollutants, particularly during winter months when temperature inversions occur, preventing the dispersion of emissions from vehicles, domestic biomass burning, construction activities, and natural mineral emissions from nearby hot springs. The surrounding hills act as barriers to wind flow, exacerbating pollution accumulation in the valley basin.

Rajgir's air quality follows a distinct seasonal pattern shaped by its humid subtropical climate and local meteorological conditions. During winter (October to January), pollution peaks dramatically due to a combination of factors: temperature inversions trap pollutants close to the ground, calm winds fail to disperse emissions, and dense fog—common in the Gangetic Plain—combines with particulate matter to form smog. This period coincides with increased tourism and domestic biomass burning for heating, making outdoor activities particularly hazardous, especially for sensitive groups like children, the elderly, and those with respiratory conditions. Spring (February to March) sees gradual improvement as temperatures rise and winds increase, though construction dust may persist. The summer months (April to June) bring extreme heat, which can elevate ground-level ozone, but stronger winds and convective activity help disperse pollutants, making this a moderately better time for outdoor exertion despite the heat stress. The monsoon season (July to September) offers the cleanest air, as heavy rainfall scrubs pollutants from the atmosphere and winds from the southwest monsoon flush the valley. However, flooding hazards can temporarily affect air quality with suspended sediments. For health guidance, sensitive individuals should avoid prolonged outdoor exposure during winter peak months, use air purifiers indoors, and schedule activities for early mornings when pollution levels are lower. The monsoon period presents the safest window for outdoor recreation.