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Thiruvallur, situated in the northern part of Tamil Nadu, India, occupies a strategic position within the Chennai Metropolitan Region's peri-urban fringe, approximately 45 kilometres northwest of Chennai city centre. The city lies on the flat coastal plains of the Coromandel Coast, with an average elevation of just 60 metres above sea level, creating a landscape dominated by alluvial soils that support extensive agricultural activities. Its geographic coordinates place it in a transitional zone between the urban sprawl of Chennai to the southeast and the rural agricultural heartlands of Tamil Nadu to the west and north. This urban–rural gradient significantly influences air quality, as Thiruvallur experiences pollution from both urban sources like vehicle emissions from district traffic and rural sources including agricultural burning and brick kiln operations. The city is intersected by several minor rivers and canals, notably the Kosasthalaiyar River flowing to its south, but these water bodies do little to mitigate pollution due to their seasonal nature and limited cleansing effects. Proximity to the Bay of Bengal, about 50 kilometres east, brings maritime influences that occasionally disperse pollutants, yet the region's industrial belt—stretching from Chennai through Thiruvallur—contributes to persistent background pollution. The flat terrain inhibits natural ventilation, allowing pollutants to accumulate, especially during calm weather conditions common in the tropical wet-and-dry climate.

Thiruvallur's air quality follows a distinct seasonal pattern shaped by its tropical wet-and-dry climate and regional meteorological factors. During the northeast monsoon season from October to December, increased humidity and occasional cyclonic systems from the Bay of Bengal can trap pollutants near the surface, leading to deteriorating air quality as the months progress. The peak pollution period from November to February coincides with the post-monsoon and winter months, when cooler temperatures and frequent temperature inversions create a stable atmospheric layer that prevents vertical dispersion of emissions from vehicles, construction dust, and agricultural burning. This season also experiences reduced wind speeds and morning fog, further exacerbating pollution accumulation. Sensitive groups, including children, the elderly, and those with respiratory conditions, should limit outdoor activities during these months, particularly in early mornings when pollution concentrations are highest. From March to May, extreme heat and pre-monsoon dry spells increase dust levels, though stronger daytime winds provide some dispersal. The southwest monsoon from June to September brings the cleanest air, as heavy rainfall scrubs pollutants from the atmosphere and increased wind flow enhances dispersion. Outdoor activities are most favourable during this monsoon period, though flooding hazards require caution. Year-round, residents should monitor local air quality advisories and use protective measures like masks during high pollution episodes.