Macarthur will be one of the worst effected areas, including the planned Bringelly growth area, where ozone is already found at higher levels than the rest of Sydney.

The report, compiled by the Department of the Environment, Climate Change and Water, argues that unless the government takes additional measures to reduce emissions, population growth will boost petrochemical smog, which could ``significantly worsen Sydney's air quality, and potentially expose more people to ozone concentrations'' above national air quality standards.

Even though vehicle emission standards have been tightened, any gains are being outrun by population growth, increased car use and the popularity of heavier cars, the report noted.

Ozone is a prime component of smog, which is caused by the reaction of auto and industrial emissions with sunlight. Air with high doses of ozone causes eye, nose and throat irritations, along with respiratory symptoms and decreases in lung function.

Overall, there has been no improvement in ozone levels across Sydney since 1998, the report noted. Ozone is the third most important greenhouse gas after carbon dioxide and methane.

``The admission by the NSW government that ozone levels haven't improved and will worsen over the next 15 years is very bad news for people with asthma and a tacit admission that its air pollution policies are failing,'' said the chief executive of the Asthma Foundation NSW, Greg Smith.

``Two new power stations in the Blue Mountains and Campbelltown, both areas with a high prevalence of asthma, will only add to the problem.''

The Total Environment Centre executive director, Jeff Angel, said: ``It's a public health emergency predicting the air quality will get worse and not [doing] anything about it.''

A spokesman for the Minister of Environment and Climate Change, Frank Sartor, said part of the solution to the ozone problem is a need for national standards for small engines such as lawnmowers and leaf blowers, and product standards for adhesives, solvents and paints.