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Sri Jayewardenepura Kotte, the administrative capital of Sri Lanka, occupies a strategically important location within the Western Province, approximately 10 km southeast of Colombo. Situated on relatively flat terrain, the city’s elevation averages around 25 meters above sea level, contributing to a generally stable atmospheric layer, though susceptible to ground-level inversions. The surrounding landscape is a blend of urban development and pockets of agricultural land, transitioning into more rural areas further afield. The proximity to the Indian Ocean, roughly 15 km to the west, influences local weather patterns and can, under certain conditions, introduce marine aerosols into the air. Colombo, a major industrial and commercial hub, lies just north, and its industrial emissions and traffic contribute to regional air quality challenges. The urban–rural gradient is relatively sharp; the city itself is densely populated with government buildings, residential areas, and commercial establishments, while the immediate periphery features smaller agricultural plots and less intensive development. The Kotte wetlands, a vital ecosystem, are also nearby, playing a role in natural air filtration, though their capacity is increasingly strained by urban expansion. The city’s location within the tropical belt means it experiences high temperatures and humidity year-round, impacting pollutant dispersion and chemical reactions. The drainage patterns, influenced by the Kelani River basin, also affect localized air quality, particularly during periods of heavy rainfall and potential flooding, which can resuspend particulate matter.

Sri Jayewardenepura Kotte’s air quality follows a distinct seasonal pattern dictated by the island’s monsoon cycles. The southwest monsoon (May to September) brings increased rainfall and generally improved air quality due to frequent precipitation washing away pollutants and stronger winds dispersing them. However, heavy rainfall can also lead to localized flooding, temporarily increasing particulate matter as roads are inundated and traffic is disrupted. The inter-monsoon periods (March-April and October-November) are often characterized by calmer winds and higher temperatures, creating conditions conducive to temperature inversions, particularly during the morning hours. These inversions trap pollutants near the ground, leading to periods of poorer air quality. The northeast monsoon (December to February) brings drier conditions and less frequent rainfall, which, combined with cooler temperatures, can result in stagnant air and increased concentrations of pollutants, especially during periods of fog. The months of January and February are generally considered the least favourable for outdoor activities for sensitive individuals, such as children and the elderly, due to the potential for elevated pollutant levels. During the monsoon seasons, while overall air quality tends to be better, individuals with respiratory conditions should still be mindful of pollen counts and potential allergens carried by the wind. Maintaining indoor air quality through proper ventilation and air purification can be beneficial throughout the year, but especially during the drier months.