The Delhi government is launching a pilot project to test advanced catalytic converters on BS3 and BS4 vehicles. This targets older cars and two-wheelers that continue to operate in the city despite their higher emission levels compared to BS6-compliant vehicles. It will help address air quality issues in the National Capital Region, particularly during the winter months when pollution levels rise.
What The Pilot Involves
The project will retrofit selected BS3 and BS4 petrol and diesel vehicles with advanced catalytic converters designed to significantly reduce harmful exhaust emissions. These devices, developed with newer catalyst compositions and improved flow designs, aim to lower nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM) emissions beyond the original equipment capabilities.
Testing will be carried out under real-world driving conditions to measure emission reductions, fuel efficiency changes, and potential impacts on vehicle performance. The pilot will cover a limited fleet, with vehicle categories including passenger cars, motorcycles, and light commercial vehicles. The project will be implemented by the Delhi Pollution Control Committee in collaboration with IIT Delhi or the International Centre for Automotive Technology (ICAT) for testing and validation.
Technical Rationale
Catalytic converters in BS3 and BS4 vehicles were designed to meet older emission norms, with reduced efficiency compared to modern BS6 after-treatment systems. Over time, these units can also lose effectiveness due to catalyst degradation. Advanced retrofit converters use higher precious-metal loadings, improved substrate materials, and optimised cell geometry to increase conversion efficiency for a wider range of exhaust temperatures.
If the trial proves successful, the Delhi government may recommend mandatory retrofitting for certain categories of older vehicles still allowed to operate in the city. This could be implemented alongside existing restrictions under the Graded Response Action Plan (GRAP) and vehicle-age limits. The programme may also inform potential amendments to the Central Motor Vehicle Rules to permit large-scale retrofits with type-approved components.
Challenges
While advanced catalytic converters could extend the usable life of BS3 and BS4 vehicles from an emissions standpoint, the retrofit cost will be in the thousands of rupees and might not appeal to all. There are also concerns over workmanship quality, long-term durability, and whether retrofitted vehicles would consistently meet improved standards without regular maintenance and periodic emissions testing.
Next Steps
The Delhi government has indicated that data from the pilot will be analysed over several months, with results expected to shape future policy. If rolled out citywide, the measure could become one of the more targeted interventions for reducing urban vehicular emissions without imposing blanket bans on older vehicles.
