Levels of nitrogen dioxide in Oxford city centre have fallen since a Low Emission Zone (LEZ) was introduced, a preliminary study has shown.
The scheme targeting emissions from buses began in January 2014 and initial figures show that levels of pollution fell through the year.
Emissions did not exceed the average hourly target of 200 micrograms of nitrogen dioxide per cubic metre.
Oxford City Council described it as a “good result”.
The city was the second outside of London to adopt a LEZ scheme.
It encouraged buses which account for up 80% of the pollution in the city centre to reduce their emissions through measures like banning them from keeping their engines running for more than one minute at a bus stop.
Preliminary results from the first year of the initiative show that nitrogen dioxide emissions recorded by a sensor at St Aldate’s did not exceed the hourly target threshold of 200 micrograms per cubic metre at any point in 2014.
The hourly target was exceeded 12 times in 2013 and 58 times in 2012.
Nitrogen dioxide is a combustion product in exhaust gas created by road traffic.
Phil Southall, managing director of the Oxford Bus Company, said £19m had been invested in the last six years in electric hybrid buses.
Ian Halliday, air quality officer at Oxford City Council, said: “This is seen as a good result. We are now turning our attention to freight and delivery vehicles, which are the next biggest source of pollution on the roads.”