Vellore occupies a strategic position in northern Tamil Nadu, situated approximately 140 kilometers west of Chennai along the Palar River basin. The city's geography is characterized by flat to gently undulating terrain with an average elevation of 220 meters above sea level, nestled between the Eastern Ghats to the west and the coastal plains to the east. This topographic setting creates a natural basin effect that traps air pollutants, particularly during the cooler months when temperature inversions become frequent. Vellore's urban character blends historic fort architecture with rapidly expanding peri-urban zones, creating a distinct urban-rural gradient where agricultural lands transition into industrial and residential areas. The city lies within Tamil Nadu's leather processing belt, with numerous tanneries concentrated along the Palar River, whose seasonal flow patterns influence local humidity and particulate dispersion. Proximity to major transportation corridors like National Highway 48 ensures constant vehicle emissions, while the city's position in the rain shadow of the Western Ghats results in relatively low annual rainfall except during the northeast monsoon. Surrounding landscapes include dry deciduous forests to the northwest and irrigated agricultural zones producing rice and sugarcane, whose burning residues occasionally contribute to regional haze. The urban heat island effect intensifies local pollution chemistry, particularly during summer months when high temperatures accelerate photochemical reactions.

Vellore's air quality follows a distinct seasonal rhythm shaped by its tropical wet-and-dry climate. During the winter months from December through March, pollution reaches its peak as cool, stable atmospheric conditions create persistent temperature inversions that trap vehicle exhaust, industrial emissions, and construction dust near ground level. Morning fog frequently combines with particulate matter to form dense smog, making these months particularly challenging for respiratory patients and outdoor exercisers. The summer season from April to June brings extreme heat that accelerates photochemical smog formation, though occasional pre-monsoon thunderstorms provide temporary cleansing through wet deposition. The southwest monsoon from July to September offers the cleanest air as sustained winds from the Arabian Sea disperse pollutants and rainfall scrubs the atmosphere, making this period ideal for outdoor activities despite high humidity. The northeast monsoon from October to November brings moderate rainfall that suppresses dust but can increase mold spores, requiring asthmatics to remain vigilant. Sensitive groups including children, elderly residents, and those with pre-existing respiratory or cardiovascular conditions should minimize outdoor exposure during winter mornings and summer afternoons, when pollutant concentrations are highest. The Christian Medical College's substantial medical traffic adds consistent local emissions year-round, but this impact diminishes during monsoon periods when atmospheric mixing is strongest.