Air quality is Truro has declined to such an extent that Cornwall Council is considering special measures to improve it.
The initiative would require officials to monitor levels of air pollution and draw up an action plan.
Air Quality Management Areas (AQMAs) are already in force in Camborne, Pool, Redruth, and Tideford.
New AQMAs were declared for Gunnislake and St Austell in March 2014. Cornwall Council is now consulting with the public about declaring another AQMA in Truro.