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Minnāl, a small town in Tamil Nadu, India (13.0744°N, 79.5590°E), is situated within the broader Tamil Plain, a relatively flat coastal region. Its elevation is low, typical of the area, contributing to limited natural dispersion of pollutants. The town’s geography is heavily influenced by its proximity to the Bay of Bengal, approximately 20km east, which introduces high humidity and seasonal monsoon winds. Surrounding Minnāl are predominantly agricultural lands, primarily rice paddies and coconut groves, interspersed with small-scale brick kilns and stone crushing units – potential sources of particulate matter. The urban-rural gradient is sharp; Minnāl itself is a concentrated settlement amidst a largely agrarian landscape. This proximity to agricultural practices introduces seasonal biomass burning, particularly after harvests, impacting local air quality. The lack of significant topographical features like hills or valleys restricts airflow, exacerbating pollution build-up during calm weather conditions. The regional climate is tropical, with high temperatures and distinct wet and dry seasons. Industrial activity is limited within Minnāl itself, but the larger industrial belts of Chennai, located further north, can contribute to regional background pollution levels that affect Minnāl, particularly during adverse meteorological conditions. The town’s small size means pollution sources are relatively close to population centres, increasing exposure.

Minnāl experiences a distinct wet and dry season cycle that profoundly impacts air quality. The dry season, from January to May, sees consistently higher pollution levels. Lower humidity and stagnant air masses trap pollutants from local sources like brick kilns and vehicle emissions. March and April are particularly challenging, with increased dust from agricultural activities and potential for localised fires. The onset of the southwest monsoon in June brings a temporary respite, with rainfall effectively washing away particulate matter and improving air quality. However, increased humidity can also foster mould growth, impacting respiratory health. The northeast monsoon, arriving in October and lasting through December, brings heavier rainfall and generally cleaner air, though localised flooding can disrupt drainage and create stagnant water, potentially breeding mosquitoes and increasing the risk of waterborne diseases. November and December are generally the most favourable months for outdoor activity. During the monsoon seasons, wind speeds increase, aiding dispersion, but also carrying pollutants from wider regional sources. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during the dry season and monitor conditions closely even during the monsoon, as short-term spikes can occur.