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Cheyyar is a small but strategically positioned city in Tamil Nadu's Tiruvannamalai district, situated approximately 100 kilometers southwest of Chennai in India's southeastern peninsula. Nestled at coordinates 12.6600°N, 79.5400°E with an elevation around 100 meters above sea level, Cheyyar occupies a transitional zone between the Eastern Ghats foothills to the west and the flat coastal plains extending toward the Bay of Bengal to the east. The city's urban character blends traditional South Indian market town elements with modern transport infrastructure, serving as a crucial junction where National Highway 38 intersects with several state roads, creating a bustling transit hub. This location places Cheyyar within Tamil Nadu's northern agricultural belt, surrounded by extensive paddy fields, sugarcane plantations, and scattered palm groves that define the rural landscape. The Cheyyar River, a seasonal tributary of the Palar River system, flows through the city but remains dry for much of the year, contributing minimal moisture to the local atmosphere. This semi-arid terrain combined with Cheyyar's position in the rain shadow of the Western Ghats creates a dust-prone environment where construction activities and unpaved rural roads generate significant particulate matter. The city's air quality is profoundly shaped by its dual identity as both agricultural center and transport corridor—vehicular emissions from diesel trucks and buses mixing with biomass burning residues from surrounding farmlands. Cheyyar's modest population of 36,000 belies its regional importance as a commercial node, with small-scale industries and bustling markets adding to the urban pollution load while the lack of significant water bodies nearby reduces natural air cleansing mechanisms.

Cheyyar's air quality follows a distinct seasonal rhythm shaped by its tropical wet-and-dry climate and regional meteorological patterns. During the northeast monsoon season from October to December, relatively calm winds and cooler temperatures create stable atmospheric conditions that trap pollutants near the surface, particularly from November through February when agricultural biomass burning peaks post-harvest and festive fireworks add to the mix. These months represent Cheyyar's most polluted period, with frequent morning fog combining with transport emissions to create hazardous breathing conditions—sensitive groups should avoid outdoor exertion during early hours and consider N95 masks when pollution is visibly dense. The brief winter from January to February brings temperature inversions that further concentrate pollutants, making these the least favorable months for respiratory patients and outdoor enthusiasts. From March to May, extreme heat dominates with temperatures exceeding 40°C, creating convective winds that temporarily disperse pollutants but also whip up construction and road dust, requiring hydration and sun protection for outdoor workers. The southwest monsoon from June to September brings Cheyyar's cleanest air as heavy rains wash pollutants from the atmosphere and winds from the Arabian Sea provide ventilation—this period offers the best conditions for outdoor activities despite occasional cyclone threats. However, drought years can diminish this cleansing effect, while flooding events might stir up sediment and waste. Year-round, Cheyyar's position as a transport junction ensures baseline pollution from diesel vehicles, but strategic timing of outdoor activities to late monsoon months and using air purifiers during inversion periods can significantly reduce exposure risks.