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Particulate matter and nitrogen oxides from traffic are not good for your health - hardly anyone doubts that. How much pollutants but make sick, is controversial and difficult to formulate. For example, in a recent study, scientists have calculated that traffic worldwide is responsible for 385,000 premature deaths, in Germany for 13,000 premature deaths. The figures come from the environmental research institute ICCT (International Council on Clean Transportation), which uncovered the diesel scandal at VW in September 2015.

In terms of population size, according to the ICCT study, nowhere do more people die of road exhaust emissions at an early stage than in Germany. According to the report, there are 17 premature deaths per 100,000 inhabitants in this country. According to the ICCT, this death rate is three times higher than the global average and is just over 50 percent above the average for all EU countries. One of the main reasons for this is the high proportion of diesel vehicles that emit particulate matter and nitrogen oxides (NOX), according to the study.

What is the problem?

A death is premature if a person dies before reaching their statistical life expectancy at birth. The unit says nothing about how much shorter a person lives, so whether he or she statistically died on average a few hours or several years earlier.

In the current ICCT study, the researchers calculated what percentage of the deceased would have statistically been alive in a year if the pollutant load from the car exhaust had not existed. "In the report, we focused on premature deaths because it is easier for the public to understand," the researchers explain in a statement.

Exactly that is questionable, because even among statisticians, the unit of measurement is controversial. "At first, not a single person dies of particulate matter in Germany, but rather of diseases that may (have) been caused by particulate matter, but they do not have to be," criticized statistician Katharina Schüller recently. At that time it was about a study of the Max Planck Institute, which also used the unit of measure "premature deaths". Schüller called the concept a "prime example of an unstatistic".

The ICCT study also critically assesses them. Behind the identification of premature deaths was not just data, but also assumptions about reality. These are associated with an uncertainty of at least 30 percent. "More serious from my point of view, that the study suggests a precision and security, which is simply not given," she said on request of SPIEGEL. This type of science communication is grossly negligent. "It leads to significant misjudgments in the validity of data and statistical models in the general public," says Schüller.

The problem is that the numbers obviously carry something different than what they think. Because premature deaths are not clinically identifiable deaths, even if it sounds like that. The Federal Environment Agency (UBA) had used premature deaths as a unit in a study and was scolded by scientists.

In a statement, the Uba rejected the criticism, however: With the indication of premature deaths do not give - as it reads for most laymen - how many real people died before reaching their statistical life expectancy of fine dust and nitrogen oxides. Much more of these are "indicators of the state of health of the whole population", that is to say: exhaust gases are assigned risks that have a general impact on the life expectancy of the population, but not individuals, which cause real deaths.

Which alternatives are there?

Another measure of the health effects of particulate matter and ozone are years of life lost (YLL). The life expectancy that a person has at birth also serves as a comparative measure. In the current ICCT study, the authors state that in 2015, humanity would lose 7.8 million years of life worldwide due to particulate matter and ozone. Spread over a world population of about 7.3 billion people at that time, it is just over nine hours that a person has lost on average.

That sounds a lot less dramatic. But it should also be clear that this measure alone is not good enough to quantify the health risks of particulate matter and NOX - at least not globally. More precise would be a consideration at least for nations, better still for regions. For air pollution in India, for example, is greater than in Canada. But even within a country, there are massive differences: New Delhi is considered the smog capital of the world, in the north Indian mountainous region, however, the air is likely to be quite good.

A study from August 2016 puts the lost lifetime through particulate matter pollution in Germany, for example, at 0.39 years. By contrast, in some African and Asian countries, where particulate matter in the air is particularly high, people lose on average up to 1.9 years of age. However, the study was concerned with general air pollution and not explicitly with traffic caused by it.


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Another way to show how much a particular factor affects health within a population is called disability-adjusted life years (Dalys). They are calculated as the sum of lost years of life (YLL) and the years of life lost due to illness. The unit of measure thus gives an impression of how much a certain factor affects the health during life.

Such projections are generally faced with the problem of correctly assessing the health risk of a single factor. An example can clarify this: Statistically, a person living on a busy street dies earlier than one who lives in the countryside. The unproven conclusion that exhaust fumes from busy roads should be responsible for premature death alone would be wrong. Because other factors could play a much bigger role: Maybe the person lives on the street, because he has little money and the rent is cheaper there? Does it therefore eat unhealthier and less sports than the one who can afford a detached house in the countryside?

There are models that can be used to calculate such factors, but they are associated with uncertainties. The results are therefore to be understood as an approximation and do not represent a clearly measurable, actually existing quantity.

How do nitrogen oxides affect your health?

Nitrogen oxides are two gaseous compounds that are abbreviated together as NOX. The corrosive irritant nitrogen dioxide reaches the body mainly during breathing and penetrates to the lungs. Above a certain level, it can irritate the respiratory system causing chest pain, shortness of breath and coughing. People who are exposed to increased exposure to nitrogen dioxide for an extended period of time are at increased risk for asthma, respiratory infections, and cardiovascular disease. Particularly at risk are persons with underlying diseases as well as children, as their respiratory tracts are still developing.

In addition to ammonia and other gases, nitrogen oxides are a precursor to the formation of particulate matter - the other group of air pollutants in the current debate.

How does particulate matter affect the body?

The problem with particulate matter is that the smaller the particles, the more they penetrate the body when inhaled. Particles of less than ten microns in size (PM10) remain mostly in the upper respiratory tract, the throat, trachea or bronchi. By contrast, PM2.5 (less than 2.5 microns) can reach the alveoli.

The ultrafine particles (UFP) can even pass into the bloodstream and thus in principle reach all body regions and cause damage there. It is believed that UFP, among other things in the blood vessels trigger inflammation processes in the vessel walls and thus promote arteriosclerosis and the formation of blood clots.

Unlike nitrogen oxides, the harmful effects of particulate matter are clearly demonstrated. Particulate matter irritates the respiratory tract and mucous membranes, causing respiratory problems such as coughing, dyspnoea, and asthma. The particles can also be involved in the development of lung cancer. If they get into the blood, they also cause damage there, the risk of cardiovascular diseases - cardiac arrhythmia, arteriosclerosis and infarction - increases.

In summary: Fine dust and nitrogen oxides burden the health. However, extrapolations that quantify the health damage caused by premature deaths are controversial because they suggest that real people have died as a result of exhaust fumes. In fact, the measure should convey an impression of the general state of health of the population. In relation to Germany, therefore, not 13,000 "real" people have died from exhaust fumes. The unit lost lifetime avoids this misunderstanding, but is so far rarely used.