LAHORE (Pakistan) • The anti-smog squad van careened through choking traffic in Lahore, on its way to track down factories belching out smoke - a seemingly futile task in one of the world's most polluted cities.

Inside the white vehicle sat an armed escort protecting the six members of the team, who clutch a list of locations they plan to inspect that day. They scan the grey, heavy sky for telltale plumes of toxic smoke that indicate a factory is breaking environmental laws.

"All we need to do is follow the smoke to get to the source, we don't even need the lists," said Mr Ali Ijaz, the environment department official in charge of the new operation, which is due to run for a month until mid-December.

The operation's five squads are the latest effort by the authorities in Lahore, near the border with India, to curb an annual pollution spike that has left more than 11 million residents gasping for air.

Mr Ijaz said they intended to visit 300 industrial factories in the sprawling metropolis that have been identified as being responsible for the worst emissions.

Air quality in India and Pakistan has deteriorated in recent years, with winter's hazardous pollution driven by a mixture of low-grade diesel fumes and smoke from seasonal crop burn off, worsened by the colder temperatures.

Lahore is routinely ranked as one of the world's most polluted urban centres, and frequently tops daily rankings.

The hazardous air quality can cause breathing issues that range from discomfort to respiratory tract and heart diseases.

But the authorities have been slow to act, blaming the smog on arch-rival India or claiming the figures are exaggerated.

This year the pollution has settled in earlier than usual, blanketing the city in stagnant, dirty grey air for days. Last week, provincial chief minister Usman Buzdar called it a "calamity".

But the authorities do not want to shut factories for more than a few days at a time, because the low-wage labourers are paid by the day. Then there is the sheer scale of the task.

"There are thousands of industrial sites releasing emissions that cannot be tackled by six or 12 squads within just Lahore," said environmental lawyer and activist Rafay Alam, dismissing the smog squad initiative as "cosmetic".

Mr Ijaz also does not hold out much hope. Even if they could shut down all of the city's factories and cut traffic, that would only "reduce the smog's intensity, but not eliminate it", he says.

"We will face this for the long-term."

AGENCE FRANCE-PRESSE