Air pollution 'kills 13,000 a year' says study

“Air pollution from exhaust fumes kills more than twice as many people as road accidents,” The Daily Telegraph has reported. The paper said that around 1,850 people die in traffic accidents annually, but that each year over 5,000 people will die as a result of heart attacks and lung cancer caused by vehicle exhaust fumes.

These estimates are based on a study that modelled the levels of pollution across the UK and predicted its impact on premature deaths. The study combined UK and EU emissions data with models of weather and the ways in which chemicals disperse. This allowed researchers to estimate the impact of pollution across the UK. According to the model, pollution from overall UK combustion emissions causes approximately 13,000 premature deaths a year, with road transport being the biggest source. A further 6,000 deaths are estimated to be due to European Union emissions produced outside the UK.

Long-term exposure to particulate matter (pollution) has been associated with premature death in many previous studies. By analysing the spread of people across the country, this new research provides an interesting estimate of how the UK population is specifically affected. However, although this sort of study can provide useful projections, its results are only estimates. In particular, although particulate matter has been associated with premature mortality in other studies, a definitive cause-and-effect link has not yet been demonstrated.

Where did the story come from?

The study was carried out by researchers from the Massachusetts Institute of Technology and was funded by the UK Engineering and Physical Sciences Research Council. The study was published in the journal Environmental Science and Technology.

The research was covered accurately in the newspapers.

What kind of research was this?

This modelling study estimated the number of early deaths each year in the UK due to combustion emissions. Sources of combustion emissions include vehicle engines, power stations, aircraft, manufacturing and burning fuel in the home. The research used estimates of emissions produced in the UK and mainland Europe and modelled how they affect regional air quality in the UK. The researchers then estimated how emissions from various sources contributed to air quality-related deaths in the UK.

This sort of study can provide useful estimates, but the figures are only based on theoretical models. In particular, although particles of pollution have been associated with premature mortality in other studies, a definitive causative link has not yet been demonstrated. The authors of this research say that there is a 90% chance that long-term exposure to fine pollution particles can lead to early death (in other words, there is a 10% chance that it does not).

While most research seems to support associations between pollution and negative health outcomes, there are many variable factors that may not be reflected by such models. For example, the study did not look in close detail at groups of people sometimes suggested to be at greater risk from traffic fumes, such as young children, people with lung problems and cyclists riding through heavy traffic. Therefore, the research provides generalised estimates across the population, but not much detail on who might be affected or how.

What did the research involve?

The researchers created a model to assess the levels of emissions across the UK and how they could affect the health of the population. They particularly looked at particulate matter with a diameter of less than 2.5µm, as research has generally suggested that long-term exposure to this type of fine particulate matter is associated with early death. A µm is also known as a micrometre, and there are 1,000µm in 1mm.

The researchers used a weather forecasting model and a regional chemistry-transport model to see how UK and European emissions could become distributed. Emissions and their sources were taken from the 2007 National Atmospheric Emissions Inventory for the UK, and EU emissions from similar European audits. The researchers validated their model by comparing it to the UK National Air Quality Archive, which has data on levels of ozone, nitrogen dioxide and particulate matter from a set of measurement stations. Ozone and nitrogen dioxide are both pollutants produced as a result of combustion, and measuring their levels in air samples provides an indicator of the amount of pollution in a location. Although ozone is important for blocking out harmful rays from the sun, this occurs when it is suspended in the ozone layer many kilometres up in the atmosphere. When found at ground level, ozone is toxic to living organisms.

Previous studies have consistently found that long-term exposure to small particulate matter of 2.5µm or less is associated with increased risk of premature mortality. For example, the US Environmental Protection Agency has estimated that there would be a 1% decrease in annual all-cause deaths for each microgram of small particulate pollution removed per cubic metre of air per year. The researchers used this association to estimate early deaths in the UK due to long-term exposure to particulate matter.

What were the basic results?

By applying emissions data to weather and chemical distribution models and the distribution pattern of the UK population, the researchers estimated that particulate matter from UK combustion emissions causes approximately 13,000 premature deaths a year. When the source of emissions was analysed, transport emissions (from road and other transport) were found to be the biggest cause of death, causing approximately 7,500 premature deaths a year. Road transport alone is estimated to cause 4,900 deaths. Power generation caused approximately 2,500 and industrial emissions approximately 830 premature deaths a year. A further 6,000 deaths are caused by non-UK emissions produced in the European Union.

How did the researchers interpret the results?

The researchers concluded that “the road transport sector is found to be the major contributor” of particulate matter and that “the resulting premature mortalities are comparable to the 2,946 deaths due to road traffic accidents in 2007, indicating that the public health impacts of road transport are likely to be 50% greater than fatal accidents.”

They also concluded that “policy measures should be coordinated at an EU-level” given the major way particulate matter from pollution can spread between nations. They also said that “the EU as a whole is responsible for air quality in any given member state.”

Conclusion

Previous research has suggested an association between long-term exposure to some forms of air pollution and an increased risk of premature death. While the link has not yet been conclusively proven, it is an important area for health research given the patterns of exposure some people may face. This study combined data on emissions in the UK and EU and models of weather and chemical distribution to model how particulate emissions (pollution) could be distributed across the UK.

By comparing their model with population density at sites across the UK, the researchers estimated how many premature deaths occur in the UK due to pollution. They estimated that particulate matter from UK combustion emissions causes approximately 13,000 premature deaths a year, with transport emissions being the biggest source. A further 6,000 deaths are estimated to be due to non-UK European Union emissions.

This sort of study can provide useful projections of the impact of pollution. However, the figures are only predictions and have been calculated using estimates and assumptions. That is not to say they are not important or valuable. However, on their own they highlight an issue for further exploration rather than definitively showing how many extra deaths are caused by pollution in the UK. As the researchers say, although particulate matter has been associated with premature mortality in other studies, there is still a degree of uncertainty over its effects and a causative link has not yet been definitively demonstrated.