ROAD traffic is now considered by the Environmental Protection Agency to be the most significant source of air pollution.
Before 1990 the worst offender was bituminous coal, which caused high levels of smog in Dublin.
The principal pollutants emitted by traffic are listed in the report as nitrogen dioxide, ground level ozone, fine particles, carbon monoxide and a variety of "volatile organic compounds".
At College Street, Dublin, the levels of nitrogen dioxide have twice almost breached the EU limit. The lower guideline value has been exceeded in each of the six years since a monitoring station was established there.
Nitrogen dioxide, which affects "the respiratory system, also 55 ground level ozone levels have increased by about 50 per cent since 1980, and traffic is the most important cause.
Measures such as exhaust filters on cars can help but, the report says, it will be some time before enough vehicles to make a difference are equipped with controls such as three way catalysts.
Maximum recorded hourly concentrations of ground level ozone "very rarely exceed" the threshold level (180 microgrammes per cubic metre), it says, adding that a national network to monitor this pollutant has now been set up.
A special investigation of volatile organic compounds and fine particulate matter is also under way. Lead, the report finds, is no longer a serious problem unleaded petrol now accounts for 58 per cent of all petrol sales.
The report also singles out transport - both road traffic and aircraft - as a major source of environmental noise. It says bypass roads can cut down significantly on the number of people exposed to high noise levels.
Although Dublin's coal smog problem has been solved and similar controls are now in place in Cork, the report notes that the EU smoke limit has been approached in Dundalk.
Referring to climate change, it says Ireland's emissions of carbon dioxide - the main greenhouse gas - are set to increase by 20 per cent, while the EU target is to abilise emissions at 1990 levels by the year 2000.
The report repeats earlier assessments that the consequences, of climate change could include serious damage to peatlands, more winter flooding and inundation and erosion of some coastal areas due to sea level change.
According to the EPA, radio activity is the most serious pollutant from abroad; notably that caused by the accident at Chernobyl 10 years ago, the risk of other accidents, and Sellafield's contamination of the Irish Sea.
Regarding acid rain, it says that although serious effects are not apparent in Ireland, it has been estimated that "imports" account for half the annual deposition of sulphur and up to 90 per cent of nitrate.
Emissions of sulphur dioxide, which also affects the respiratory system, fell by 30 per cent from 1980 to 1993, mainly through switching to natural gas and reducing the sulphur in coal burned at Moneypoint, Co Clare.