Lewisham Council will fine motorists who idle up to Â£80 from next year.
The plans were rubber-stamped at a meeting of Mayor and Cabinet on September 18 and will apply to all roads in the borough.
The RAC says idling engines produce levels of CO2, NO2 and PM2.5 over two times as many as those in motion, with most instances coming from â€˜avoidableâ€™ road situations such as waiting to pick someone up outside a workplace or school.
Cllr Sophie McGeevor, cabinet member for Environment and Transport, said: â€˜We urgently need to change public attitudes to idling as many donâ€™t realise the risk this poses to peopleâ€™s health and the environment.
â€˜Air quality in London is a public health crisis and we all have a part to play in reducing air pollution. We hope fining drivers for idling will deter them from doing this â€“ the overall benefit from the small action of switching off car engines while stationary cannot be underestimated.â€™
Itâ€™s been an offence to leave a â€˜vehicle engine running unnecessarilyâ€™ since 1986, and powers were handed to councils in 2002 in England to issue fixed penalty notices of Â£20 if motorists refuse to turn their engine off when asked to by a traffic warden.
However, in practice enforcement has been difficult. In March, an AirQualityNewsÂ investigation revealed that of the five councils who said they were actively fining motorists throughout 2018,Â only a handful of fines were issued,Â with campaigners saying the current system is â€˜not fit for purposeâ€™.
In July, the Department for Transport launched a consultation to look at different ways of tackling idling, including raising the fine.
In March, Public Health England (PHE) published a review of evidence on how to improve air quality which recommended councils ban vehicles from idling outside pollution hotspots such as schools or hospitals.