A report commissioned by Oxford Friends of the Earth shows 22 sites across the county have breached the annual Air Quality Objective for Nitrogen Dioxide (NO2) levels.
The data compares air levels of nitrogen dioxide, the agreed maximum limit is 40ug/m3 as defined in the Air Quality Objective.
Sitting atop the list with nitrogen oxide levels double that of the 40ug/m3 limit is Banbury's Hennef Way with a reading of 84.8ug/m3. Second on the list was a Botley road with a reading of 60.9.
Chipping Norton and Banbury Horsefairs also made the list at 9th (48.1) and 14th (41.8) respectively.
UK Friends of the Earth is campaigning for Clean Air Zones to be developed in affected areas, supported by measures such as improved infrastructure to support safe cycling and walking and improved public transport.
Chris Church, for Oxford Friends of the Earth, said: “It’s unforgivable to see so many locations across our county over air quality limits, leaving thousands of us breathing dangerously polluted air.
"These figures show how air pollution is not just an issue affecting cities. Unacceptably toxic air can be found now in smaller towns. It is harming the health of people across the country and is especially bad for young children whose lungs are still developing.
"The government and our local councils need to step up and do more to deal with this air pollution crisis. We need clear and committed action.
He added: "We are concerned that in November 2017 Oxfordshire County Council voted to take ‘immediate action’ and to set up an Air Pollution Action Group (APAG) to be led by county and district councillors with officer input. Fifteen months on, that Group has not yet met even once. This is simply unacceptable.”
High levels of NO2 can cause a flare up of asthma or symptoms such as coughing and difficulty breathing. A leading cause of NO2 pollution is emissions from road traffic.
Oxfordshire County Council said in a statement: "Oxfordshire County Council is committed to working in partnership with district councils to improve air quality.
"County council members passed a motion in 2017 to set up an Air Pollution Action Group. Since then, we have been working closely with the districts on many joint initiatives to reduce pollution levels.
"These include plans for a Zero Emission Zone in central Oxford, Bicester and Barton Healthy New Towns, and helping everyone across the county switch to healthier and more environmentally friendly modes of transport such as walking and cycling, or moving towards electric vehicles.
"We’re confident that by working together on individual projects, and by listening to residents, we will be successful in improving the county’s air quality."