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Olagadam, nestled in the Thiruvannamalai district of Tamil Nadu, India (11.5656° N, 77.6428° E), occupies a geographically significant position within the Eastern Ghats. The city’s terrain is gently undulating, transitioning from the relatively flat plains of the Kaveri delta to the foothills of the Eastern Ghats, a range characterized by ancient, eroded rock formations. This location influences Olagadam’s microclimate and, consequently, its air quality. The surrounding landscape is a mosaic of agricultural fields – predominantly rice paddies and pulses – interspersed with scrubland and pockets of dry deciduous forest. The Kaveri River, though not directly adjacent, exerts an indirect influence through its impact on regional humidity and prevailing wind patterns. Olagadam’s proximity to the industrial belt around Salem, approximately 80 kilometers to the north, is a crucial factor. While not directly within the industrial zone, Olagadam experiences downwind transport of pollutants, particularly during periods of low wind speed. The urban–rural gradient is relatively sharp; Olagadam itself is a small, primarily agricultural settlement, with a gradual transition to more intensive farming and scattered villages in the surrounding areas. Elevation plays a minor role, with the city situated at an average altitude of around 150 meters, limiting the potential for significant vertical dispersion of pollutants. The prevailing winds, generally southwesterly, carry moisture from the Bay of Bengal, but also potentially transport pollutants from industrial sources further inland.

Olagadam’s tropical climate dictates a distinct wet and dry seasonal cycle, profoundly impacting air quality. The southwest monsoon (June to September) brings relief from accumulated pollutants, as frequent rainfall and increased wind speeds effectively ‘wash’ the atmosphere. Humidity levels rise significantly, which can trap particulate matter at times, but the overall cleansing effect of the monsoon generally leads to improved air quality during these months. The pre-monsoon season (March to May) is typically the most challenging. Rising temperatures, coupled with decreasing rainfall and stagnant air, create conditions conducive to the build-up of pollutants. Temperature inversions, where a layer of warm air traps cooler air near the ground, are more frequent during this period, exacerbating the problem. The post-monsoon season (October to November) sees a gradual improvement as the monsoon recedes, but lingering humidity and occasional fog can still contribute to localized pollution episodes. Winter months (December to February) are generally characterized by cooler temperatures and calmer winds, which can lead to a build-up of pollutants, particularly during periods of fog. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the pre-monsoon and winter months, limiting outdoor exertion and monitoring for any adverse health effects. Agricultural burning, a common practice in the region after the harvest, can also significantly impact air quality during these periods, creating localized spikes in pollution.