The results have prompted environment officials to look at strategies to reduce the number of cars, revealed Public Commission for the Protection of Marine Resources, Environmental and Wildlife director-general Dr Ismail Al Madani.

"The number of vehicles has increased by nine per cent in the last year, which is very worrying," he told the GDN.

"For the time being I don't think pollution levels are that dangerous, but they are definitely a warning for the future." One of the main concerns is an increase in ozone gas (O3), which protects the earth against ultraviolet radiation but is harmful when inhaled at ground level.

The amount of low-level O3 in Bahrain has increased from 37 parts per billion (ppb) in 1996 to 51ppb.

It is the result of vehicle exhaust and industrial emissions, petrol vapours and chemical solvents - as well as natural sources - emitting NOx and volatile organic compounds, which form ozone when combined with sunlight.

According to the US Environmental Protection Agency (EPA), ozone triggers a variety of health problems and may cause permanent lung damage after long-term exposure, as well as damage plants and the ecosystem.

There has also been a sharp rise over the past 10 years of nitrogen oxides (NOx), which the EPA says are among the main causes of smog, acid rain, respiratory problems, global warming and poor quality of water. Vehicles are a primary source of NOx, which rose in Bahrain from 15ppb 10 years ago, reaching a peak of 30ppb in late 2002 and dropping again to 24ppb according to the latest tests.

Sulphur dioxide (SO2), which is pumped into the atmosphere by industries such as petroleum refineries, cement manufacturers and metal processing facilities, have been relatively stable in Bahrain at under 5ppb over the last 10 years.

There were spikes upwards to 10ppb in 1998 and 9ppb in 2002, but the figure currently stands at 7ppb. SO2 also contributes to respiratory illness and acid rain. However, Bahrain's air quality tests showed that certain parts of the country are more polluted than others.

"The Central and the Northern Governorates are the most polluted due to the large number of vehicles and industries," said Dr Al Madani.

He added that although industries do contribute to air pollution, they are being forced to clean up their act.