The introduction of catalytic converters into cars and other vehicles may have helped reduce childhood asthma rates, new research has found.
Episodes of acute asthma in children in the Republic rose steadily in the latter part of the 20th century and have since declined.
Researchers at the National University of Ireland Galway (NUIG) suggest the reduction in environmental pollution that resulted from lower emissions from cars is the reason why the number of asthma attacks in children has reduced.
Gerard Loftus, professor of paediatrics at NUIG, and colleagues from the Environmental Change Institute at the college looked at admission rates for acute asthma for children aged one to 14 years at University College Hospital Galway from 1985 until 2004.
They also examined environmental pollution data for the same period in the form of black smoke concentration levels measured at three different sites in Galway city.
They found that the admission rates for children with asthma and air pollution levels followed the same pattern, with both rising to a peak in the mid-1990s.
Then from 1995 onwards, both the smoke levels and the asthma admission rates dropped steadily.
According to the authors of the study, which was presented at the annual meeting of the Irish Thoracic Society, it shows an apparent one-year time-lag between air pollution levels and admission rates.
The relationship was especially marked among pre-school children aged one to four years but the drop in hospital asthma admissions also occurred in five to 14 year-olds.
Prof Loftus told The Irish Times that the drop in asthma cases in those aged one to four was particularly significant, as these children were not treated with preventive inhalers, making it more likely the reduction in asthma was due to lower pollution levels rather than preventive treatment.
The relationship between air pollution from cars and childhood asthma was probably due to the children's exposure to nitrogen oxide and other particulate matter while they were travelling in cars and buses, the authors suggested.
They detected a seasonal increase in smoke levels in September of each year, coinciding with the beginning of the school commute.
Catalytic converters remove nitrates, carbon monoxide and volatile organic compounds from car exhaust emissions.
Prof Loftus said the results of the study needed to be replicated in other cities in Ireland and the UK.
However, he said that if the Galway studies were reproduced internationally, then it would be clear that engine emissions were hazardous to children and should be reduced.
Asthma is a chronic breathing condition causing wheeze and breathlessness which worsens during an acute attack.
There are some 470,000 people with asthma in the Republic; an estimated 80-100 asthma-related deaths occur here each year. Ireland has the fourth highest prevalence of asthma in the world.