NO _X -VOC-O ₃ sensitivity in urban environments of Sri Lanka

Physical phenomenon of the relation among the ground level O ₃ , NO _X and VOC governed by complex nonlinear photochemistry in urban environments is explained in detail using the ambient pollutant concentration data of eleven cities in Sri Lanka. The time-series analysis was conducted using the 24-hour average ambient concentrations of PM ₁₀ , NO ₂ , CO, O ₃ and SO ₂ air pollutants obtained from fixed air pollution monitoring station located in Colombo since 2008. Further analysis was carried out from the mobile air pollution monitoring station for eleven cities. The hourly averaged ambient real time air quality data i.e. VOC, NO ₂ , NO, O ₃ pollutants and the corresponding meteorological parameters were analyzed and presented in weekly results for the base year 2013, 2014 and 2015. It was identified that there exist two regimes of NO _X -VOC-O ₃ sensitivity among these cities. Colombo, Kurunegala, Jaffna, Matara, Badulla, Pollonnaruwa, and Gampaha are the NO _X -sensitive regime. While Rathnapura, Anuradhapura, Kandy and Nuwaraelliya are the VOC-sensitive regime. In the NO _X -sensitive regime (with relatively low NO _X and high VOC), O ₃ increases with the increasing NO _X and slightly changes in response to the increasing VOC levels. In the NO _X -saturated or VOC-sensitive regime, O ₃ decreases with increasing NO _X level and increases with increasing VOC levels. In the immediate vicinity of very large emissions of NO, O ₃ concentrations are depressed through the process of NO _X titration. Mathematical relationships were developed to calculate the steady state ozone concentration (O _3ss ) that gives the values for both NO _X -sensitive regime and the VOC-sensitive regime. Establishment of these relationships are essential for Sri Lanka to develop the appropriate interventions for controlling O ₃ pollution in each city.