Seven hundred drivers of the highest polluting vehicles are to receive advice from Bristol City Council about how they can reduce emissions.
A laser beam scans particles in the exhaust to work out emissions
The worst-emitting vehicles were caught by new technology which can remotely detect vehicle emissions.
Some 65,000 vehicles were monitored by council officials along seven major routes in the city. Over 4,000 were found to exceed accepted standards.
The council will advise the motorists to get their cars serviced.
"Efficient driving and eminence not only reduces local pollution and CO2, it also benefits the pockets," said a council spokesperson.
The spokesperson added that drivers can save up to £400 per year by changing their maintenance habits and having vehicles regularly serviced can cut fuel consumption by 25%.
Officials caught the worst-offending vehicles in November using new technology which measures the emissions by shining a laser beam through the exhaust path.
Councillor Dennis Brown said: "This type of emissions testing will help further the council's work on reducing air pollution in and around Bristol.
"The information gathered is helping us to advise drivers of high polluting vehicles that they should have their vehicle checked and any faults corrected.
"I would strongly advise all drivers to get hold of a copy of the booklet and to save themselves money and help clean up the city," he said.
The booklet, 'Cut Your Car Costs' is part of the council's Air Quality Action Plan.