Bath and Bristol streets exceed EU pollution levels
Dozens of streets across Bristol and Bath exceed European air pollution levels, the BBC has learnt.
Bristol City Council said reducing the amount of traffic to meet the European target was "difficult".
Nitrogen dioxide is a gas, emitted mainly by diesel vehicles, which can cause inflammation of the lungs.
In 1999, the European Union set an objective for every member state to lower nitrogen dioxide levels to fewer than 40 micrograms per cubic metre of air by 2010.
Local councils have a responsibility to monitor air quality. This information is then made publicly available.
In 2010, 90 Bristol streets out of 123 monitored by the council registered levels above the EU limit.
Rupert Street, a busy bus route in the centre of Bristol, had the highest level of nitrogen dioxide, at 102.6 micrograms per cubic metre - more than twice the recommended European limit.
Steve Crawshaw, air quality manager at Bristol City Council, said: "In order to meet these targets there is only one way, and that is a drastic reduction in traffic.
"And it's very difficult to meet that when people need to travel around. It's very difficult to know what we could do to meet those targets - there are no easy answers I am afraid."
Epidemiologist Dr Frank Kelly, from Kings College, London, said: "We know it's a pollutant gas which has biological effects much along the lines of the other pollutants we know about that come out of the back of vehicle exhausts.
"At this point in time it's an unknown risk, it's unquantified - we need to be able to quantify the extent of damage that's occurring".
In Bath, 33 out of the 76 streets which were monitored, exceeded the limit. Lambridge, which leads to the city centre, had the highest level at 81 micrograms per cubic metre.
Jo Holley, lives on London Road in Bath, which has a level of 49 micrograms per cubic metre.
Talking about her twin eight-year-old daughters who both have asthma, she said: "Asthma takes over our life really, particularly Molly's life at the moment.
"It really annoys me that the levels are extremely high - I think it's something that needs to be addressed as a country."
Claire Holman, from environmental consultancy, Environ, said: "Twenty years ago we all thought that air quality was going to be improved, all the targets and limit values would be met.
"Yet we're in this position 20 years later where we still are some way off."
Last month, the government applied to the EU for an extension after it failed to meet the 2010 deadline to reduce nitrogen dioxide levels.