| Abstract | Economic growth in developing countries had led to a boom in the number and use of vehicles. The rapid increase in the vehicle population in conjunction with the limited use of emission control technologies, has made the transport sector the largest contributor to ambient air pollution in Sri Lanka. Although, Sri Lanka has not yet experienced any acute air quality problems, the projected rates of economic and vehicular growth can lead to rapid deterioration of the air quality. Therefore, there is an urgency to eliminate the unintended consequences of transportation.
Motorized on-road vehicles have an overwhelming dominance over the transport sector in Sri Lanka and they are expected to do so for the foreseeable future. The lack of adequate data regarding on-road emissions delays the actions needed to appraise, mitigate and control air pollution. Therefore, within the scope of this work, a comprehensive on-road emission inventory was developed for Sri Lanka, from 2010 to 2040, using the dynamic vehicle population model within the framework of the SPEW-Trend. Exhaust emissions of PM10, CO, HC and NOx were determined under the four fuel consumption scenarios described by the SAARC Energy Center for Sri Lanka. Emissions were determined by dividing fuel use among various vehicle technologies. The vehicle technology share is a given year was determined by the timing of emission standard implementation, vehicle retirement rates and super-emitter generation rates. Emission factors were assigned to each technology variant and the total emissions from 2010 to 2040 was determined, annually, by integrating emissions of different vehicle technologies, types and all ages.
The active vehicle fleet in Sri Lanka is composed of 35% motor cars, 29% three-wheelers, 27% motorcycles, 6% goods transportation vehicles and 3% buses. The average age of motor cars is 16 years, motorcycles and three-wheelers are 8 and 9 years respectively and buses and goods transportation vehicles are 14 years. More than 50% of the motor car, motorcycle and goods transportation vehicles are imported as second hand vehicles in to the island. Majority of the motor cars in Sri Lanka originate from Japan, while three-wheelers, motorcycles, buses and goods transportation vehicles originate predominantly from India. Vehicle activity of all vehicle types decrease continuously with age. The average annual mileage was determined to be 9612km, 5958km, 5451km, 33156km and 13218km for motor cars, motorcycles, three-wheelers, buses and goods transportation vehicles respectively. Equilibrium super-emitter fraction of motor cars, motorcycles, three-wheelers, buses and goods transportation vehicles were determined to be 11%, 21%, 27%, 10% and 12% respectively. Historical fuel consumption data revealed that annual diesel consumption by the transport sector is 70% and goods transportation vehicles dominate fuel consumption. In 2040, emissions are projected to be 2.92 – 3.2 kton of PM10, 85.5 – 101.5 kton of CO, 13.3 – 15.1 kton of HC and 79.5 – 88.8 kton of NOx. PM10, CO and HC emissions decrease continuously despite the increase in fuel consumption. NOx emissions increase throughout the study period however; the rate of increase reduces continuously with time. PM10 and NOx emission intensities are the highest under the MASSTRANS scenario. HDDVs contribute to 80 - 91% of the total PM10 emissions and 70 – 93% of the total NOx emissions. On average super-emitters contribute to over 30% of the total PM10, HC and CO emissions and over 20% to NOx emissions.
This is the first on-road emission inventory developed for Sri Lanka and the results thus obtained can be used as scientific input for effective air quality management in Sri Lanka. |