POLLUTION levels in the heart of the city have bucked the national trend by getting worse, with the rise blamed on increased traffic.
The Scottish Environment Protection Agency (Sepa) has queried why vehicle exhaust emissions are soaring above EU targets on Princes Street, West Maitland Street, Roseburn Terrace and York Place.
A council report published today also reveals that Easter Road has been identified as a new area of concern due to high levels of pollutants.
The council is now set to monitor the street and special measures to reduce pollution may need to be introduced.
It will also investigate why nitrogen dioxide is increasing on the four city centre roads, when cleaner vehicles and fuels should have the opposite effect.
In total, there are at least nine pollution hotspots in the Capital, with five - West Maitland Street, Princes Street, Roseburn Terrace, Torphichen Place and St John's Road - all expected to fail EU targets on air quality when they become mandatory in 2010.
The council faces being hit by thousands of pounds in penalties, so it is considering 60 fines for motorists who drive vehicles that spout high levels of pollution and reducing parking charges for smaller, more environmentally-friendly cars.
And while trams and more park-and-rides facilities are also expected to make a big difference, officials have admitted that "low-emission zones" - which prevent some vehicles entering certain areas of the city - may have to be looked at in the future.
Councillor Ricky Henderson, the city's transport leader, said today: "One of the downsides of living in a city as prosperous as Edinburgh is that the growth in population leads to a growth in traffic volumes.
"While we certainly do not want to discourage people from using their cars for necessary journeys, our environment cannot sustain the level of growth and this has had an adverse effect on our air quality in certain areas.
"It's no coincidence that the areas with poorer air quality follow the line of the proposed tram route.
"Trams have no tailpipe emissions and will undoubtedly help improve our air quality. However, we know this is a few years off and we have to act now.
"Park-and-rides are part of the solution, as buses and trains can carry large numbers of passengers into the city quickly. Plus we are behind Lothian Buses and their efforts to upgrade all their engines to cut emissions.
"But we also need to work with the other public transport providers to ensure that they too are replacing older engines and are helping to provide part of the solution that will lead to an improvement to air quality in the city."
Long-term exposure to nitrogen dioxide can decrease lung function and increase the risk of respiratory illnesses such as bronchitis, particularly in children.
The EU annual average objective for nitrogen dioxide is 40 micrograms per metre cubed, but the latest figures show that an average of 77 micrograms was recorded at the junction of West Maitland Street and Palmerston Place, and 69 micrograms at Roseburn Terrace and Roseburn Street.
Gorgie Road at the Murieston Road junction, North Bridge and Queen Street at Frederick Street are all currently at or above the EU target, but pollution levels are dropping. Elsewhere - in the New Town, Morningside, Grassmarket and Newington - all monitored areas are improving.
The council recently designated St John's Road an "air quality management area", where special measures are planned to reduce pollution.
The council has warned the problem there could worsen due to Edinburgh Airport's expansion plans.
Great Junction Street in Leith and West Port could be next in line for the classification, possibly followed by Easter Road.