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Vellarivalli, nestled in the Thiruvannamalai district of Tamil Nadu, India, occupies a geographically significant position within the Eastern Ghats foothills. Located at approximately 11.6003° N latitude and 77.7927° E longitude, the town’s elevation averages around 150 meters above sea level, contributing to a relatively mild climate. The surrounding landscape is characterized by a blend of undulating hills, agricultural plains, and pockets of dry deciduous forest, typical of the region. Vellarivalli’s proximity to the Ponnai River, a tributary of the Pennar River, provides a crucial water source and influences local microclimates, potentially moderating temperatures and humidity. The town sits within a transitional zone, exhibiting a gradual urban–rural gradient. To the west, the landscape rises towards the Eastern Ghats, while eastward, it flattens into fertile agricultural lands primarily used for rice and pulses cultivation. This agricultural activity, while vital to the local economy, can contribute to seasonal particulate matter pollution, particularly during harvest periods when burning of crop residue is practiced. Further afield, the industrial belt around Ranipet, approximately 80 kilometers northwest, represents a potential source of industrial pollutants that can be transported by prevailing winds. The town’s relatively small population (13,408) suggests a primarily rural character, though increasing connectivity and potential for future development could alter this dynamic and impact air quality in the coming years. Topography plays a role; valleys can trap pollutants, while higher ground experiences better dispersion.

Vellarivalli’s tropical climate dictates a distinct wet and dry season pattern, profoundly influencing its air quality. The dry season, typically spanning from March to May, is characterized by high temperatures and low humidity. This period often witnesses a noticeable increase in particulate matter pollution, largely due to agricultural practices. The burning of crop residue after harvest, a common practice to clear fields quickly, releases significant amounts of smoke and pollutants into the atmosphere. Calm wind conditions during this period exacerbate the problem, allowing pollutants to accumulate locally. Temperature inversions, where a layer of warm air traps cooler air near the ground, are also more frequent, further hindering vertical mixing and trapping pollutants. The monsoon season, from June to September, brings relief with increased rainfall and stronger winds, effectively flushing out pollutants and improving air quality. However, heavy rainfall can also lead to increased humidity and the potential for fungal spores, impacting respiratory health. The post-monsoon period (October-November) sees a gradual decrease in rainfall and a return of calmer conditions, potentially leading to a renewed rise in pollution levels. December and January are generally cooler and relatively cleaner, although fog formation can reduce visibility and trap pollutants close to the ground. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak pollution periods and wearing appropriate masks when necessary. Maintaining indoor air quality through ventilation and air purifiers is also advisable.