Cape Town's dirty skies exceeded the international levels for air pollution almost every day last week.

The City of Cape Town's air quality statistics show that air pollution guidelines for human safety were exceeded every day between Saturday, July 9, and Thursday, July 14, at some or all of the monitoring stations. The city air pollution department calls these "red days".

On many days, the dirty skies extended way out to sea, creating a brown smudge over False Bay and Table Bay.

The worst "red day" was measured on Monday last week in Goodwood, where the amount of suspended dirt particles measured 127 micrograms a cubic metre of air. The European guideline for human health is 50 micrograms of particulate matter a cubic metre.

Although Europe has set this as a benchmark, the World Health Organisation has set no guidelines as it maintains that there is no safe limit for breathing in particulate matter, which is carcinogenic.

Most particulate matter comes from the tailpipes of vehicles.

An air pollution study done for the city some years ago showed that 66 percent of air pollution came from vehicle emissions, 22 percent from industry and about 11 percent from domestic fires.

The results of a new study, which used an aircraft to collect air samples in addition to samples taken on the ground, are due to be released this month.

Monitoring stations are situated in Bellville, Athlone, Bothasig, central Cape Town, Goodwood, Khayelitsha, Killarney, Pinelands and Table View.

The stations which recorded more than one red day last week, where the pollution levels were classified as "high", were Goodwood and Khayelitsha. One red day was recorded at Table View.

Even those days where the pollution levels were recorded as "moderate", still exceeded the European guidelines. These occurred on several days last week in central Cape Town, Table View, Goodwood, Bellville South, Bothasig, Khayelitsha and Killarney.

Although the pollution was bad, the city council received only one complaint from the public, which may indicate that Capetonians have become used to dirty skies in winter.

There was also photochemical smog over the city on some days last week, where sunlight turns nitric oxides from vehicle tailpipe emissions into another pollutant, nitrogen dioxide.

The City of Cape Town, which has been monitoring air pollution for 20 years, is in the process of developing an air quality management plan.

The plan has been put out for public comment, and the authorities are now consolidating the input. The plan focuses on setting air pollution guidelines for the city.

Air pollution affects not only the natural environment and human health but, for a city which sells its scenery to foreign visitors, may have a negative impact on tourism.

Anton Moldan, environment adviser for the South African Petroleum Industries Association, said by next year sulphur in fuel would have to be reduced from 3 000 parts per million to 500: "This will have a significant effect on air pollution and will reduce particulate matter."

By February last year all new models of cars had to be fitted with catalytic converters and by 2008 all new cars will have to have them.

"The converters will reduce pollution, but it is essential for vehicles to be properly maintained. There is no point in having cleaner fuel if poorly maintained vehicles are going to continue to belch out black smoke," Moldan said.

Andy Gubb, of the Wildlife and Environment Society, said it was critical that the authorities solved the public transport problem. This would not only reduce air pollution but would help the economy and society.

He said the Transport Act had identified public transport as a priority.