Stand beside the Kingsway coast road and you have an almost constant stream of cars, vans and lorries for company.

Besides the vehicles is a less obvious and quieter danger - nitrogen dioxide and particulates spewing from hundreds of exhaust pipes.

The two pollutants are the ones causing the most concern in Sussex today.

Acute exposure to either can lead to a host of respiratory problems and can cause fatalities among the very young, the very old, or people particularly susceptible.

Long-term exposure can also cause problems but it takes longer for the symptoms to show.

For particulates, tiny particles that penetrate deep into the lungs, there is no longer thought to be any safe level of exposure.

Councillor Steve Collier, who represents Portslade South on Brighton and Hove City Council, said: "The reason why they are dangerous is the particles are about one-third of the size of pollen grains, if not smaller.

"Our bodies can deal with pollen grains but not things that are that much smaller."

His ward includes one of the busiest parts of the A259, which includes the Kingsway, and he does not believe the monitoring being done is enough to gauge levels of pollution, particularly particulates, in the air nearby.

He said testing was not continuous and if it was done on a wet day, for example, it would produce a lower result than a dry day, when particulates were blown into the air.

Coun Collier said: "They are not monitoring 365 days a year, so we are not getting the true picture."

Testing for pollution on Kingsway, just like elsewhere in the city, is the job of Brighton and Hove City Council.

There are three monitoring stations which record air quality every 15 minutes all year: At the Royal Pavilion, Hove Town Hall and Foredown Tower.

A fourth, mobile station is used to troubleshoot in areas where there may be a problem and there are another 40 sites where filter papers are checked every month.

The council said pollution throughout the city was below the targets in the Government's Air Quality Strategy and Kingsway was no different from anywhere else.

The strategy, introduced in 2000, requires councils to declare air quality management areas in places where pollution levels are a problem.

A council spokesman said: "As we are nowhere near close to any of the objectives we don't need to declare one."

As well as nitrogen dioxide and particulates there are also targets for benzene, carbon monoxide, 1,3-butadiene, lead and sulphur dioxide.

But in many cases the objectives have been relaxed since the Conservatives published the first strategy in 1997.

Then, particulates were only permitted to exceed the recommended limit on four days a year. Today, they are able to pass for 35 days a year.

A review of the strategy, in part prompted by new EU regulations, is likely to bring in tougher limits for all pollutants by 2010.

Tim Brown, deputy secretary of the Brighton-based National Society for Clean Air, said many councils had reviewed their air quality and they were now hoping for the best.

He said: "Some little market towns have declared air quality management areas because they think they are going to exceed the limit, so they are going to do something about it.

"On the other hand, the whole of the West Midlands are saying we will just about scrape by. I think that is what is happening in Brighton.

"The bottom line is whether Brighton thinks it has got a problem and whether it has proven to everyone's satisfaction that no action needs to be taken."

No council in Sussex has so far needed to take special measures. All are broadly in line with, or better than, councils in Hampshire, Kent and Surrey but there are some hotspots.

Andrew Deacon, who heads the Sussex Air Quality Steering Group, said: "There are parts of Shoreham, parts of Eastbourne, parts of Hastings and parts of Brighton which are fairly close to the objectives for nitrogen dioxide and particulate matter."

New air quality reviews, which each council has to carry out every three years, should lead to a gradual improvement as the tougher standards come into force.

Mr Deacon said: "The moves we are seeing longer term are good ones because we are clamping down on the more dangerous ones, like particulates.

"The problem is, medically speaking, there is no level you can set for compounds like particulates and benzene.

"There is no limit that is absolutely no risk to health. You will always be compromising."