Motorists outside 20 schools in Sheffield are set to be fined for leaving engines running, starting when schools go back in September.
-> GCSE results 2018: Leeds and West yorkshire live GCSE results guidePolice posted the warning on their Facebook page but the scheme is being run by Sheffield Council.
Other areas in Yorkshire could well follow suit.
The fines will be brought in at schools where the highest levels of pollution have been found in the air, the council said.
Sheffield Council engineer Chris Galloway said in a report: "In common with many major cities, Sheffield has problems with poor air quality, particularly around major roads.
"Sheffield roads have concentrations of nitrogen dioxide forecast above legal limits.
-> Shocking images show why Yorkshire woman was convicted over death of six pets"Engine idling is a significant factor to air pollution in some areas of the city such as the taxi rank near the Midland Train Station.
"It is a preventable and unnecessary source of emissions, particularly at locations with sensitive receptors such as children."
Drivers caught will have to pay a £20 fixed penalty notice.