Vellār, nestled in the Thiruvannamalai district of Tamil Nadu, India, occupies a geographically significant position within the Eastern Ghats. Located at approximately 11.89°N, 77.96°E, the town’s terrain is characterized by gently undulating hills and plains, typical of the region's transition zone between the Deccan Plateau and the coastal plains. The elevation, though modest, contributes to localized microclimates and influences air circulation patterns. Vellār’s proximity to the Pennar River, though not directly on its banks, provides a degree of humidity and influences regional weather systems. The surrounding landscape is a mosaic of agricultural fields – predominantly rice and pulses – interspersed with scrubland and pockets of dry deciduous forest. This agricultural activity, while vital to the local economy, can contribute to seasonal particulate matter emissions, particularly during harvest periods. The urban–rural gradient around Vellār is relatively gradual; the town itself is small, with a population of just over 11,000, and blends seamlessly into the surrounding agricultural landscape. Further afield, the industrial belt centered around Thiruvannamalai, with its mix of granite processing and small-scale manufacturing, represents a potential source of pollutants carried by prevailing winds. The town’s location within a relatively sheltered valley can also lead to the trapping of pollutants, especially during periods of low wind speed. The overall topography, combined with agricultural practices and distant industrial influences, shapes Vellār’s unique air quality profile.

Vellār experiences a tropical wet-dry climate, significantly impacting its air quality throughout the year. The dry season, typically spanning from March to May, is characterized by high temperatures and minimal rainfall. This period often sees a noticeable increase in particulate matter concentrations, stemming from agricultural burning – a common practice for clearing fields – and increased dust due to drier conditions. Temperature inversions, where cooler air becomes trapped beneath a layer of warmer air, are also more frequent during these months, hindering vertical mixing and exacerbating pollution. The monsoon season, from June to September, brings relief with increased rainfall, effectively washing away pollutants and significantly improving air quality. However, the onset of the monsoon can initially be accompanied by increased humidity and fog, which can temporarily trap pollutants near the ground. October and November represent a transitional period, with decreasing rainfall and gradually increasing temperatures. December and January are generally cooler and drier, with relatively stable air quality, though occasional fog events can still impact visibility and trap pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season (March-May) and be mindful of potential fog events throughout the cooler months. Outdoor activities are generally more favorable during the monsoon season (June-September) and the cooler, drier months of December and January, though agricultural burning can still pose a localized risk during the transition periods.