Vehicles may be polluting more than you think despite passing PUC tests

Despite passing Pollution Under Control (PUC) tests, many vehicles on Indian roads are likely emitting more pollutants than their emission standards permit, TOI reported citing a new study by the International Council on Clean Transportation (ICCT).

The study reveals that even vehicles adhering to the latest BS VI norms release significantly higher emissions in real-world conditions compared to laboratory settings.

The ICCT's analysis used remote sensing technology to measure pollutants such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter from 1.1 lakh vehicles at 20 locations across Delhi and Gurgaon.


The findings highlighted that commercial vehicles contribute more to pollution than private ones, with BS VI-compliant CNG taxis and light goods vehicles emitting 2.4 and 5 times more NOx, respectively, than their private counterparts.

The study challenges the perception of compressed natural gas (CNG) as a “clean” alternative fuel. It was discovered that the real-world NOx emissions of BS VI CNG vehicles, including three-wheelers, private cars, taxis, and buses, were multiple times higher than the type-approval limits, which are based on laboratory tests.

Type approval certificates are granted to vehicle manufacturers once their vehicles meet specific technical and safety standards, allowing them to be sold in the market. The study was part of the Real Urban Emissions (TRUE) Initiative, conducted in collaboration with authorities in Delhi and Gurgaon.

While the leap from BS IV to BS VI emission standards in India has resulted in substantial reductions in tailpipe emissions, the study notes that real-world emissions for BS VI vehicles still exceed type-approval limits, especially for NOx. For example, while real-world NOx emissions from private cars decreased by 81% and from buses by nearly 95%, they still remained higher than expected.

Given that vehicles are a major source of air pollution in Delhi, the study points out significant gaps in the PUC certification process, which fails to measure key pollutants like NOx and particulate matter and does not account for real-world emissions. The study suggests that PUC tests should be complemented with real-world technologies like remote sensing, a practice currently only used in Kolkata since 2009.

Amit Bhatt, India Managing Director at ICCT, emphasized the need to rethink India’s emissions testing system and push for the adoption of zero-emission vehicles (ZEVs). "For the first time in India, we have collected significant emissions data from vehicles on the road, and what impacts our air quality is not the laboratory emissions but the pollutants released by these vehicles while on the road," TOI quoted Bhatt as saying.

Anirudh Narla, a researcher at ICCT India, highlighted that remote sensing technology can effectively screen tailpipe emissions from vehicles on a large scale under real-world conditions, helping to identify highly polluting vehicles.

The report also recommends finalizing and publishing the Automotive Industry Standard (AIS) 170, which would establish the technical parameters for remote sensing devices and equip authorities to measure vehicle exhaust in real-time.

Sheila Watson, Deputy Director of the FIA Foundation, remarked, "This important research clearly shows India and the rest of the world that CNG is not the clean alternative fuel which was promised."

Anumita Roychowdhury, Executive Director of Research and Advocacy at the Centre for Science and Environment, stated that remote sensing as an on-road surveillance method could not only help identify the worst polluters but also provide insights into the emissions performance of different technologies and fuels.

"This shows that while the CNG transition has helped cut toxic particulate emissions from diesel vehicles during the early years, NOx emissions from on-road CNG vehicles without adequate controls can be high. This builds a case for the next big transition to electrification to make tailpipe emissions not cleaner but zero," she added.

(With TOI inputs)