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Chālil, a municipality nestled within the Kollam district of Kerala, India, occupies a relatively low-lying coastal plain at approximately 11.75°N latitude and 75.59°E longitude. The city’s geography is profoundly shaped by its proximity to the Arabian Sea, with the Ashtamudi Lake forming a significant inland waterway nearby. This backwater ecosystem, characteristic of Kerala, influences local humidity and wind patterns. The terrain is generally flat, gradually rising inland towards the Western Ghats, though Chālil itself remains close to sea level. Surrounding the urban core are extensive coconut plantations and paddy fields, indicative of Kerala’s agricultural heritage. While Chālil isn’t a major industrial hub, the broader Kollam district hosts cashew processing units and small-scale manufacturing, contributing to localised emissions. The urban-rural gradient is relatively sharp, transitioning quickly from densely populated areas to agricultural landscapes. This coastal location means Chālil is susceptible to sea breezes, which can both disperse and concentrate pollutants depending on atmospheric conditions. The dense vegetation offers some natural filtration, but the flat terrain can limit dispersion during stagnant air events. The city’s position within a tropical climate zone dictates high humidity and consistent temperatures, impacting pollutant chemistry and atmospheric stability.

Chālil experiences a distinct wet and dry season, heavily influenced by the Southwest Monsoon. Air quality generally improves during the monsoon months (June-September) as heavy rainfall effectively washes particulate matter from the atmosphere. However, increased humidity can also promote the formation of mould and secondary pollutants. The post-monsoon season (October-November) sees a gradual return of drier conditions and a corresponding increase in dust and localised emissions from agricultural activities like paddy harvesting and burning. December to February represents the driest period, often characterised by calmer winds and temperature inversions, trapping pollutants near the ground. This is typically when air quality is poorest, particularly in the mornings. March to May brings rising temperatures and increased convective activity, which can offer some dispersion, but also exacerbate ozone formation. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during the dry season, especially in the mornings. Monitoring local weather patterns and avoiding peak traffic hours are advisable. The monsoon, while bringing relief, can also increase the risk of waterborne diseases, so maintaining hygiene is crucial.