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Negombo, a coastal city in Sri Lanka’s Western Province, presents a unique geographic context influencing its air quality. Situated at 7.2111°N, 79.8386°E, the city lies on a narrow strip of land between the Indian Ocean and the Negombo Lagoon, a brackish water body vital to the local fishing industry. The terrain is predominantly flat, with elevations rarely exceeding 10 meters above sea level, making it vulnerable to sea breezes and stagnant air conditions. Negombo’s urban character is a blend of fishing communities, tourism-focused development, and expanding residential areas. The city serves as a key transport hub, with close proximity to Bandaranaike International Airport, contributing to localised emissions. Surrounding the urban core are coconut plantations, rice paddies, and pockets of mangrove forests along the lagoon. An increasing urban-rural gradient is evident as one moves inland, with agricultural practices contributing to seasonal biomass burning. Industrial activity, though not concentrated in massive belts, is present in the form of fish processing plants and smaller manufacturing units, adding to the pollution load. The coastal location means air quality is heavily influenced by prevailing winds and marine aerosols, alongside land-based sources. This interplay creates a complex pollution profile.

Negombo experiences a tropical monsoon climate, dictating a distinct wet and dry season rather than traditional four seasons. Air quality generally improves during the southwest monsoon (May to September) due to increased rainfall which effectively washes away particulate matter and disperses pollutants. However, the monsoon also brings high humidity, potentially fostering mould growth indoors. The inter-monsoon periods (March-April and October-November) are transitional, with fluctuating wind patterns and increased localised pollution from vehicle emissions and small-scale industries. The dry season (December to February) typically sees the poorest air quality. Lower rainfall and stable atmospheric conditions lead to pollutant build-up, exacerbated by temperature inversions common during cooler nights. Dust from construction and agricultural activities also contributes. Months to avoid prolonged outdoor activity for sensitive groups are January and February. Individuals with respiratory conditions should limit exposure during these periods. The monsoon season, while wet, offers better air quality, but precautions against waterborne diseases are necessary. Monitoring wind direction is crucial; onshore winds can bring marine pollutants, while offshore winds offer temporary relief.