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Killai, a coastal town in the Cuddalore district of Tamil Nadu, India, occupies a low-lying position near the Bay of Bengal (coordinates 11.4493°N, 79.7668°E). With a population of approximately 13,066, Killai’s geography is fundamentally shaped by its proximity to the sea and the fertile Kaveri Delta region. The terrain is predominantly flat, characteristic of the coastal plains, with a gentle slope towards the ocean. This flatness contributes to limited natural dispersion of pollutants. Surrounding Killai are extensive agricultural lands, primarily paddy fields, and coconut groves, typical of the Tamil Nadu coastline. While not a major industrial hub itself, Killai is situated within reach of industrial areas further inland, particularly around Cuddalore, which can contribute to regional air pollution transport. The urban-rural gradient is relatively sharp; Killai retains a strong rural character, but experiences increasing pressures from population growth and associated activities. The coastal location means the town is vulnerable to sea breezes, which can both dilute and transport pollutants, depending on prevailing wind directions and regional emissions sources. The lack of significant elevation hinders atmospheric mixing, potentially exacerbating pollution episodes. The sandy soil composition also contributes to dust generation, particularly during drier periods.

Killai experiences a tropical climate with distinct wet and dry seasons, heavily influencing its air quality. The dry season, roughly from January to May, sees lower rainfall and higher temperatures, leading to increased dust suspension from agricultural activities and roadways. Stagnant air masses and temperature inversions are common during these months, trapping pollutants near the ground. February and March are typically the worst months for air quality. The southwest monsoon arrives in June, bringing significant rainfall that washes away pollutants and improves air quality dramatically. However, increased humidity can also promote the formation of secondary pollutants. September and October, following the monsoon’s retreat, can see a resurgence of pollution as agricultural burning increases for land preparation. The northeast monsoon, from October to December, brings further rainfall, again offering temporary relief. During the monsoon seasons, strong winds help disperse pollutants, but also increase the risk of saltwater aerosols. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during the dry season and periods of agricultural burning. Monitoring wind direction is crucial; onshore winds bring marine influences, while offshore winds can concentrate land-based pollutants.