Two congested roads in Preston have unacceptably high levels of pollution.
The busy roads, in Broughton and New Hall Lane, have been declared air quality management areas (AQMA) following assessments of the nitrogen dioxide levels in the city.
The readings exceeded the government’s limit of 40 micrograms per cubic metre, by almost double in some areas.
Diffusion tubes are used to monitor the levels for one month and they are sent away for tests.
Two tubes were used at two points on New Hall Lane, recording levels of 51.5 and 44.6, and three on Garstang Road which had readings between 45.5 and 71.
Chris Hodson, council environmental health manager, said: “Obviously the limit is 40 so we are getting close to double the limit in Broughton.
“It’s an irritant so sufferers with respiratory problems such as asthma or something of that nature, nitrogen dioxide can bring on potential asthma attacks at severe levels.
“It’s the proximity of the residents to the road as well as pollution of this nature.
“People who have a garden, it would’ve reduced to a level below the limit but (on New Hall Lane and in Broughton), you’ve got properties within a few metres of the highway.”
Nitrogen dioxide normally comes from vehicle emissions. The council is now producing a plan to reduce levels, working with organisations including Preston Bus and the county council.
The areas are at the junction of Whittingham Lane and Garstang Road, and the western end of New Hall Lane, from the London Road junction to Acregate Lane.
There are already AMQAs in place, since 2005, at Ringway, Church Street and Percy Street in the city centre and also the A5085 Blackpool Road/Plungington Road.
A Health Protection Agency spokesman said: “At high concentrations nitrogen dioxide is an irritant and can cause inflammation of the airways.”