Do older vehicles pollute more? insights from emissions testing data in Sri Lanka

Abstract

The transport sector contributes significantly to global emissions with the rapid acceleration of global urbanization and corresponding growth in vehicle population. It is expected that as the vehicle ages and its mileage grows, the engine gradually wears out and emits more emissions. In response, many countries have implemented vehicle age limit restrictions for vehicle imports and fleet operations to control vehicular emissions. However, regular maintenance and responsible driving practices may help to minimize the overall impact of vehicle ageing on vehicle conditions and hence, reduce emissions. Despite this, the overall influence of vehicle age on emissions, along with other influencing factors, remains debatable. This study aims to investigate the overall influence of vehicle ageing on tailpipe emissions using emissions test data from the Vehicle Emission Testing (VET) Programme in Sri Lanka. The analysis focuses on RE205 (made by Bajaj Auto Ltd, India) petrol tricycles tested between 2012 and 2022, examining the behavior of hydrocarbon (HC) and carbon monoxide (CO) emissions in relation to vehicle age. Notably, the results indicate a more considerable change in CO emissions compared to HC. Further, CO emissions show a gradual increase during the first five years of vehicle life, followed by a gradual decrease over the next one to two years. After six to seven years, emission levels remained relatively constant. These findings indicate that, as expected, emissions tend to rise in the early years due to aging effects until they exceed regulatory emission limits, after which they relatively remain constant. Corrective maintenance measures, taken after exceeding the regulatory limits, appear to bring emissions down to the regulatory limits. The subsequent low and relatively constant emission levels are likely due to continued maintenance practices. Overall, the findings highlight the critical role of regular maintenance in managing and reducing emissions as vehicles age.