Headline: Lung doctors for more pollution? – A Q&A on the debate about limit values

How dangerous is air pollution for my health? Many cyclists in German cities ask themselves the same question.
How dangerous is air pollution for my health? Many cyclists in German cities ask themselves the same question. istock/Thomas_EyeDesign

Last week in Germany, retired pulmonary physician Dieter Köhler made waves by publishing a statement, signed by over one hundred other fellow lung doctors, calling into question the science behind air quality standards and suggesting that current EU-wide limits for nitrogen oxides and fine particulate matter are unnecessarily strict. Not coincidentally, this comes at a time when diesel driving bans are being imposed in many German cities because of their inability to meet the EU-wide limit value for nitrogen dioxide (NO2), for which diesel cars are the main source. This has sparked debate on many levels, from the journalistic to the political. In this blog post we specifically address the topic of air quality limit values based on our expertise in the fields of air quality and public health.

Who are the experts here?

Pulmonary physicians are experts in treating individual people with lung diseases. Epidemiologists study incidences of diseases in a whole population, making use of toxicological data and large health datasets. In the field of toxicology, experimental studies are designed to investigate the impacts of single pollutants on the body. A limitation of these studies, however, is that they cannot investigate the chronic health effects of air pollution. This is where the field of epidemiology comes in: epidemiological studies are designed to investigate acute, sub-acute and chronic effects of air pollution in large populations. This means that epidemiologists – who take toxicological studies into account – are the right experts to turn to when it comes to evaluating environmental health risks. Just like you don’t go to an epidemiologist (or a neurologist, or a pediatrician) to treat your chronic lung disease, you don’t go to a pulmonary physician to evaluate environmental health risks. In Dr. Köhler’s statement, he stresses that statistical correlation is not the same as causality, and that confounding factors such as lifestyle and smoking are problematic when trying to evaluate the health effects of air pollutants. Yet all of these aspects are well known in the field of epidemiology and are already taken into account in epidemiological studies.

It is also important to note that a statement made by one doctor, even when signed by a hundred other doctors, should not be taken to represent the position of doctors in general. Indeed, these doctors are in the minority – the approximately one hundred signatories of the statement represent less than 3% of the 3,800 members of the German Society for Pneumology and Respiratory Medicine who were invited to sign it. The same medical society recently published a detailed position paper advocating for the reduction of air pollution based on scientific data.

Where do the NO2 air quality standards come from anyway?

Air quality standards in Germany and Europe are based on a precautionary approach and designed to protect human health. This means protecting everybody’s health, including the health of the most vulnerable – children and the elderly, whose respiratory tracts are especially sensitive.

To make a recommendation on what constitutes a “safe level” for this purpose, hundreds of peer-reviewed scientific studies, primarily in the fields of toxicology and epidemiology, were considered by the World Health Organization. And what is the scientific consensus? That NO2 is a lung irritant and that short-term exposure to it can cause breathing problems and asthma attacks. Children are at higher risk of respiratory illness induced by NO2, which is of particular concern since repeated lung infections in children can cause lung damage later in life. Studies on the long-term effects of NO2 exposure have found robust associations with worsened symptoms of bronchitis in asthmatic children, respiratory and cardiovascular disease, hospital visits, and overall mortality. It is not possible to say unambiguously that the relationship between these health outcomes and long-term NO2 exposure is causal, although the latest research does point in that direction. There is also evidence of NO2 health impacts even at concentrations below legal limits, and new studies are emerging that demonstrate an association between NO2 and the incidence of dementia in areas with relatively low air pollution like Ontario, Canada.

Deciding on the appropriate limit value for NO2 comes down to considering the available science, our level of risk tolerance, and making a judgement call. The German and European ambient air quality standard for NO2 of 40 micrograms per cubic meter (µg/m3) is based on the WHO’s recommendation. Switzerland has a more stringent limit of 30 µg/m3, while the US standard is higher.

If cigarettes are more harmful, why bother regulating air pollution?

We’ve seen versions of this question raised several times in the media coverage surrounding Dr. Köhler’s statement, which itself brought up the comparison to smoking. The implied logic goes something like this: We still smoke, and that’s bad for our health, so maybe driving diesel cars should just be added to the list of unhealthy things that we like to do (and then we can forget about those driving bans).

Yes, if you live in Germany, smoking cigarettes is more harmful than breathing the ambient air. But unlike smoking, air pollution is not a lifestyle choice but rather an involuntary environmental exposure. When you smoke a cigarette, the main person being harmed by the cigarette smoke is you (though second-hand smoke also affects those around you); when you drive your fossil fuel-powered car, its emissions affect the whole community – and indeed the whole world if you also consider climate impacts (via emissions of CO2 and co-emitted air pollutants) in addition to direct health impacts. At the first WHO Global Conference on Air Pollution and Health last fall, Dr. Tedros Adhanom Ghebreyesus, WHO Director General, called air pollution a “silent public health emergency” and described this health risk as the “new tobacco,” calling on us to tackle this epidemic. But in contrast to tobacco, lifestyle change at an individual level is not enough to protect us – which is why we need air quality standards and regulations as safeguards. Health is a fundamental human right, which we have a moral and societal obligation to protect – and that means protecting our clean air.

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