The pollution watchdog reached this conclusion after analysing the Capital’s air pollution for a month, including the 15 days from January 1 when road trials of the scheme were conducted.

It deduced from data that pollution levels couldn’t have gone down more than 5-10% — that too in Delhi’s central zone — even if the scheme to allow vehicles to ply on odd and even dates based on the last number of their licence plates was implemented under favourable weather.

Its findings were noteworthy since the Arvind Kejriwal government has plans for another go at the scheme from mid-February to clean up the city’s foul air by reducing the volume of toxic car exhaust fumes.

According to the pollution board, pollution levels in Delhi rose during the period when the scheme was tried out because of overcast conditions that prevented quick dispersal of pollutants.

Air pollution in areas outside the outer Ring Road and closer to satellite towns Ghaziabad, Noida, Gurgaon, Faridabad and Sonepat was almost twice as much as in congested central Delhi areas such as Mandir Marg and ITO.

“The gains were lost on the city’s outskirts,” a CPCB scientist said, blaming high air pollution levels in the NCR towns.

In fact, air pollution level in NCR towns saw a substantial increase when the odd-even scheme was on and Delhi felt the impact. On some days, Noida, Ghaziabad and Gurgaon breathed far fouler air than ITO, where the car curb scheme’s effect was clearly visible.

This has pushed the pollution board to conclude that a “comprehensive set of actions following an integrated approach is required to make substantial improvement in air quality” and suggest a slew of measures for the entire region to “effectively” combat deteriorating air quality.

It circulated a 40-point plan in the last week of December to combat air pollution in Haryana, Uttar Pradesh and Delhi. The board reinforced the action plan with the Air (Prevention and Control of Pollution) Act, 1981, thereby making its implementation legally binding.

The CPCB asked the states to get diesel vehicles retrofitted with particulate filters, put an early alarm system for commuters about congested roads, create intelligent traffic systems, place a vapour recovery mechanism in fuelling stations and develop foundations at roundabouts. All these have to be acted upon in a time-bound way.

Most of the state pollution boards have not responded to the plan, a month after it was issued. Some said it couldn’t be implemented unless the Centre provided financial assistance.

“The question is who will foot the bill. Most municipal bodies in our state do not have adequate funds to bring this transformational change,” said a Haryana government functionary, who attended a meeting on air pollution called by environment minister Prakash Javadekar in Delhi.

An official of the Uttar Pradesh pollution authority wondered how diesel vehicles could be “immediately” retrofitted with filters.

Given the constraints, experts feared the CPCB action plan would never take off unless a strong political will pushed it through to improve NCR’s air quality.