Air pollution
NO2 is a killer
Whilst the harmful impact of nitrogen dioxide (NO2) on various medical conditions was already known, only now is there evidence that NO2 in air pollution is a killer. According to the APHEA-2 study the chief culprits are emissions from diesel engines, which are increasingly popular in Europe.
In the 1990s, the Air Pollution and Health - A European Approach (APHEA) study demonstrated air pollution’s harmful impact on human health using data from some 15 major European cities. The European Commission (EC) and World Health Organisation considered these results when amending their air quality recommendations.
To enlarge the database and provide more information the second study - APHEA 2 - involving several European laboratories and 34 large cities from Scandinavia to Israel, set out to identify what specific effects could be attributed to each of the main pollutants, focusing on sooty fumes, suspended particulate matter of under 10 microns diameter (PM10), sulphur dioxide (SO2), ozone (O3) and NO2.
The European Respiratory Journal (ERJ) has published the results for NO2, a study conducted by Klea Katsouyanni, Evangelia Samoli and team at the Department of Hygiene and Epidemiology, University of Athens, Greece. Their research raises serious concerns.
The team used the largest existing European database of c. 60 million people, with pollution measurements for at least three consecutive years. Mortality and hospital admissions were compared with measurements for various atmospheric pollutants taken by the ambient air monitoring stations in each of the APHEA-2 cities.
The comparison produced some alarming results. ‘They show that short-term mortality rates (i.e. in the days directly after exposure to the pollutant) are very clearly linked to daily variations in the level of NO2, essentially an urban pollutant mainly produced by diesel engines and heating systems. A rise in atmospheric NO2 levels of ten microgrammes per cubic metre (10µg/m3) was found to increase short-term mortality by 0.30%. The statistical link retained its significance even when various confounding factors, such as the effect of other pollutants, or a flu epidemic, were taken into account. The correlation with NO2 concentrations is clearer still if we focus specifically on deaths from cardiovascular and respiratory causes in the days directly following exposure. Indeed, a rise of 10µg/m3 in NO2 levels increases deaths from cardiovascular and respiratory conditions by 0.40% and 0.38% respectively.’
The impact also varies according to length of exposure. Comparison of levels measured over six days (date of death and preceding five days) with those measured over two days (date of death and previous day) shows that 22% more cardiovascular deaths and 45% more respiratory deaths were connected with the six-day exposure. ‘This most likely reflects different physiopathological effects’, the authors point out. ‘NO2’s cardiovascular effects are generally associated with mortality in the short-term (sudden deaths without hospitalisation), while its respiratory effects tend to involve disease that will cause death at a later date,’ Klea Katsouyanni adds.
The east-west variation
In north-western and southern Europe the impact of NO2 pollution is greater than in cities in their central and eastern European counterparts. The researchers suggest a reason: ‘In the 1990s, atmospheric pollution in southern and western European cities was caused mainly by road traffic, while Eastern Europe had fewer cars at the time.’ Older people, they also add, are more vulnerable to the short-term effects of air pollution, probably due to existing respiratory conditions or other diseases. Eastern Europe’s lower life expectancy in the past might therefore account for the lower NO2 pollution impact.
Diesel
The study also shows that the effects of NO2 and PM10 can interact. NO2 seems to have a stronger impact when combined with high levels of suspended particulate matter. Both pollutants are mainly emitted by diesel engines.
Because diesel vehicles emit 40% more particulate matter, Klea Katsouyanni believes the monitoring of diesel fuel quality and diesel vehicle maintenance should be improved, and the use of these vehicles should be reduced. Diesel-powered vehicles are on the rise throughout Europe, she points out.
However, the APHEA-2 data show that urban NO2 levels do not yet exceed the EU limits - which are now being reviewed on the basis of new data from further studies. No doubt, say the authors, APHEA-2 will be considered when setting future standards.
01.07.2006
