A COMPARATIVE STUDY OF VEHICULAR AIR POLLUTION EMISSIONS FROM PETROL AND DIESEL ENGINES IN URBAN TRANSPORTATION SYSTEMS

Abstract

Background: Air pollution is a significant issue in urban areas and petrol and diesel powered internal combustion engine vehicles are the leading cause of air pollution from transportation. The two types of engines have different emission profiles, creating different environmental and public health problems. While regulation progresses, there is still a need for a comprehensive comparative analysis under realworld urban driving conditions to help inform policy decisions. Objective: The objective of this study is to compare the emission characteristics of petrol and diesel engines of light duty passenger transport vehicles (LD-PTVs) for the main pollutants such as nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), hydrocarbons (HC), and carbon dioxide (CO₂) for urban transport systems. Methodology: A systematic analytical review was conducted using secondary data from established sources, including the COPERT emission factor database, EMEP/EEA guidebooks, International Council on Clean Transportation (ICCT) real-world driving reports, type-approval test data (WLTP and NEDC cycles), and peer-reviewed journal publications. Emission values were compared across engine types, regulatory stages (Euro 1–6), and driving conditions (laboratory vs. real-world urban cycles). Key Findings: In urban driving conditions, the NOx emissions from diesel are 2-5 times higher than from petrol and the particulate emissions are much higher. But, CO₂ emissions are reduced by 15–25% and fuel consumption reduced by 20–35% in diesel. Most important, the gap between real-world NOx emissions and laboratory certification is up to 7 times higher for diesel vehicles in urban stop and go traffic than for petrol vehicles, while the gap for petrol is significantly smaller (1.2–1.5 times). Petrol engines give off more CO and HC, but modern 3-way catalytic converters are effective at reducing these emissions. Conclusion: The study findings indicate that there is no clear superiority of either engine type based on all the advantages and disadvantages: The diesel engine has climate benefits due to lower CO₂ emissions, and in urban areas, the petrol engine has better advantages in terms of reduced emissions of NOx and PM. The most successful policy route for sustainable urban mobility is to speed up the transition towards using zero-emission electric vehicles and introduce strict emission tests in real-world conditions for all internal combustion engine vehicles (Real Driving Emissions / RDE).