Truck driver Muhammad Afzal was not expecting to be stopped by police, let alone fined, as he drove into Islamabad this week because of the thick diesel fumes emanating from his exhaust pipe.
"This is unfair," he said after being told to pay 1,000 rupees ($3.60), with the threat of having his truck impounded if he did not "fix" the problem.
"I was coming from Lahore after getting my vehicle repaired. They pressed the accelerator to make it release smoke. It's an injustice," he told AFP.
Checkpoints set up this month are part of a crackdown by authorities to combat the city's soaring smog levels, with winter months the worst due to atmospheric inversions that trap pollutants at ground level.
"We have already warned the owners of stern action, and we will stop their entry into the city if they don't comply with the orders," said Dr Zaigham Abbas of Pakistan's Environmental Protection Agency (EPA), as he surveyed the checkpoint at the southeast edge of the capital.
For Waleed Ahmed, a technician inspecting the vehicles at the site, "just like a human being, a vehicle has a life cycle. Those that cross it release smoke that is dangerous to human health".
While not yet at the extreme winter levels of Lahore or the megacity Karachi, where heavy industry and brick kilns spew tons of pollutants each year, Islamabad is steadily closing the gap.
So far in December it has already registered seven "very unhealthy" days for PM2.5 particulates of more than 150 micrograms per cubic meter, according to the Swiss-based monitoring firm IQAir.
Intraday PM2.5 levels in Islamabad often exceed those in Karachi and Lahore, and in 2024 the city's average PM2.5 reading for the year was 52.3 micrograms -- surpassing the 46.2 for Lahore.
Those annual readings are far beyond the safe level of five micrograms recommended by the World Health Organization.
Built from scratch as Pakistan's capital in the 1960s, the city was envisioned as an urban model for the rapidly growing nation, with wide avenues and ample green spaces abutting the Himalayan foothills.
But the expansive layout discourages walking and public transport remains limited, meaning cars -- mostly older models -- are essential for residents to get around.
"The capital region is choked overwhelmingly by its transport sector," which produces 53 percent of its toxic PM2.5 particles, the Pakistan Air Quality Initiative, a research group, said in a recent report.
"The haze over Islamabad... is not the smoke of industry, but the exhaust of a million private journeys -- a self-inflicted crisis," it said.
Announcing the crackdown on December 7, EPA chief Nazia Zaib Ali said over 300 fines were issued at checkpoints in the first week, with 80 vehicles impounded.
"We cannot allow non-compliant vehicles at any cost to poison the city's air and endanger public health," she said in a statement.
The city has also begun setting up stations where drivers can have their emissions inspected, with those passing receiving a green sticker on their windshield.
"We were worried for Lahore, but now it's Islamabad. And that's all because of vehicles emitting pollution," said Iftikhar Sarwar, 51, as he had his car checked on a busy road near an Islamabad park.
"I never needed medicine before but now I get allergies if I don't take a tablet in the morning. The same is happening with my family," he added.
Other residents say they worry the government's measures will not be enough to counter the worsening winter smog.
"This is not the Islamabad I came to 20 years ago," said Sulaman Ijaz, an anthropologist.
"I feel uneasy when I think about what I will say if my daughter asks for clean air -- that is her basic right."
