Delhi to bar vehicles without valid PUCC from November 1
What's the story
Starting November 1, vehicles without valid Pollution Under Control (PUC) certificates will be barred from entering Delhi. The decision is part of the Commission for Air Quality Management's (CAQM) revised Graded Response Action Plan (GRAP) to combat pollution. In October, CAQM also ordered fuel stations in the area to deny service to vehicles lacking these certificates.
Emission testing
What are the implications of not having a PUC certificate?
A PUC certificate is issued after testing two gases in petrol cars while idling and measuring exhaust smoke darkness in diesel vehicles.
However, this method has been criticized for failing to detect nitrogen oxides and fine particles from modern diesel filters.
A 2018 study by The Energy and Resources Institute (TERI) and the Automotive Research Association of India (ARAI) found that vehicles emit 81% of nitrogen oxides produced within Delhi, which contribute to fine particles and ozone formation.
Certificate details
What does the law say about PUC certificates?
According to Rule 115 of the Central Motor Vehicles Rules, 1989, every vehicle older than a year must have a valid PUC certificate.
The certificate is valid for six months or 12 months for Bharat Stage IV (BS-IV) and BS-VI compliant vehicles.
State transport departments authorize private testing centers to issue these certificates.
Violating these standards can result in fines up to ₹10,000, or imprisonment for up to three months, or both.
Test parameters
How is the PUC test conducted?
The PUC test measures carbon monoxide (CO) and hydrocarbons (HC) in petrol, CNG, and LPG vehicles.
For diesel vehicles, a smoke test is conducted by flooring the accelerator while measuring exhaust opacity.
BS-IV or later vehicles may emit no more than 0.3% CO and 200 parts per million of hydrocarbons.
A 'lambda' value between 0.97 and 1.03 is also required for newer cars to ensure proper catalytic converter function.
Pollution sources
What are main sources of pollution in Delhi during winter?
Delhi's winter haze is primarily caused by particulate matter 2.5 (PM2.5), which can penetrate deep into the lungs.
A major study from November 2022 to February 2023 found PM2.5 levels averaged over three times India's national standard.
The study attributed this pollution to secondary inorganic particles (32%), biomass burning (24%), vehicles (17%), coal and fly ash (7%), municipal waste burning (3%), household fuel (3%), soil and road dust (2%), and other sources (12%).
Emission gaps
Are there any limitations in current testing methods?
Nitrogen oxides are not measured in idle tests as they form at high combustion temperatures. A 2002 World Bank review noted this limitation.
The Netherlands tests older petrol cars against limits similar to India's BS-IV standards and found no high emitters would have failed under Indian testing.
Between December 2022 and April 2023, the TRUE Initiative found BS-VI CNG vehicles emitted up to 14 times their nitrogen oxide limits, highlighting gaps in current testing methods.
Soot measurement
How vehicle emission tests can be improved
The PUC test measures exhaust smoke darkness for older diesel vehicles without filters.
However, newer diesel vehicles with particulate filters may emit smoke too faint for meters to register.
The European Commission's 2025 assessment noted that defective Diesel Particulate Filters (DPFs) can result in emissions undetectable by traditional methods.
Belgium now counts particles in exhausts instead of relying solely on opacity measurements, further highlighting limitations in current testing practices.