Mobile Sources Emissions to Ambient Air Quality: Case Study on the Baseline Road, Greater Colombo, Sri Lanka

Abstract

Understanding air quality near roads is important for mitigating urban air pollution and safeguarding public health. Empirical evidence has shown that vehicular emissions significantly contribute to elevated air pollution levels in near-road environments, as indicated by monitoring data collected predominantly during short-term campaigns worldwide. This study evaluates the contribution of vehicular emissions to near-road ambient air quality (PM2.5, CO, and NO2) in a significant segment of Baseline Road, of the Colombo metropolitan area, Sri Lanka. using the AERMOD view dispersion model. AERMOD was validated using monitored data for CO, NO2, and PM2.5. The results show that CO has a fractional bias (FB) of 0.421, a normalized mean square error (NMSE) of 0.294, a factor of two (FAC2) of 0.652, and a correlation coefficient (R) of 0.5. For PM2.5, the FB is 1.858, the NMSE is 32.865, the FAC2 is 0.037, and the correlation coefficient (R) is 0.376. NO2 has an FB of 0.727, while NMSE of 0.954, a FAC2 of 0.467, and a low correlation coefficient (R) of -0.407. The simulated results were under-predicted because only the exhaust emissions of vehicles were considered for the study. The maximum contribution of CO (>83%), PM2.5 (10%) and NO2 (77%) was observed near road junctions. However, the maximum concentrations of pollutants were below the ambient air quality standards stipulated by the Central Environmental Authority of Sri Lanka.