Nitrogen oxide: Is it really that dangerous, lung doctors ask?

Several German pulmonary physicians question the current nitrogen oxide and particulate matter limits. These are inadequate and mainly based on questionable epidemiological studies, they say.

How dangerous arenitrogen oxides (NOx) and particulate matter really? Lung doctors have now joined the debate on driving bans in city centers, designed to enforce current pollutant limits. And they are by no means unanimous in their assessment.

First, the German Society for Pneumology and Respiratory Medicine (DGP) published a position paper on December 3, in which the authors point out the dangers of air pollutants. They list the effects of various pollutants on the lungs, heart, organ system, brain and on unborn children.

They insist that a "significant reduction in air pollution is required and a lowering of the legal limit values is necessary."  The authors call for a "culture of avoiding pollutants" combined with very concrete regulatory measures.

Read more: German cities get more funding for air quality, but retro-fitting plan still to come

Epidemiological studies or rather toxicological experiments?

In principle, however, the authors point to a difficulty in the scientific definition of legal limits. As a rule, statisticians use epidemiological studies as a basis for recommendations to politicians. On this advice, the legislators then set applicable limit values.

However, epidemiology, which deals with the causes and spread of diseases within population groups based on statistics, has its limits: Since "mixtures of pollutants usually occur in road traffic, a purely epidemiological separation of the effects of individual components on the organism can be difficult or impossible," the authors of the position paper posit. In contrast, experimental toxicological studies on cells, animals or humans are more meaningful. 

Europe's battle against deadly air pollution

Cutting back on diesel

Germany has launched a scheme to retrofit its diesel public buses with exhaust-scrubbing systems, and introduce charging points to encourage drivers to switch to e-cars. Still, environmentalists say that's not enough. They want all diesel vehicles — including private cars — retrofitted, or taken off the road.

Europe's battle against deadly air pollution

Taking cars off streets

Milan, one of Italy's most polluted cities, has banned cars from its downtown area during certain hours. Other cities in Italy and abroad have experimented with similar schemes, for example permitting only cars with odd or even license plates on the road at given times in order to limit the amount of traffic.

Europe's battle against deadly air pollution

Free public transport

The Macedonian capital of Skopje is battling with pollution levels up to 15 higher than permitted by the EU — though it's not yet a member state, so isn't facing fines. Macedonia's smog problem is largely down to burning coal and emissions from aging, inefficient industry and vehicles. To get people to leave their dirty old cars at home, the government has introduced free public transport.

Europe's battle against deadly air pollution

Sounding the alarm

One street in London exceeded the EU's annual nitrogen dioxide limit on January 30 — less than a month into 2018. Actually, this is an improvement — it's the first time in a decade the British capital has kept within the annual limit for more than six days. Mayor of London Sadiq Khan has announced he wants to alert the city's schools on days when pollution is particularly bad.

No agreement among lung doctors

A group of high-ranking pulmonary physicians has also criticized the inadequacy of epidemiological studies. They do not, however, share a central conclusion of the DGP position paper — namely that legal limits should be further reduced. To date, 112 German lung specialists have signed a document opposing the validity of current nitrogen oxide and particulate matter limits.

The pneumologist and intensive care physician Dieter Köhler is the initiator of the group and recruited supporters of his position within the medical profession at the beginning of 2019.

He published an article last September in the German medical journal "Ärzteblatt" denying the "scientific basis" of epidemiological studies, used to calculate the applicable pollution limits.

Coincidence or cause?

The core of his criticism is the confusion of causality and correlation by epidemiologists. In other words: In areas with high levels of particulate matter and NOx, people die on average somewhat earlier than elsewhere. But whether they also die fromparticulate matter and NOx is completely unclear.

It could also be due to other factors: smoking, alcohol consumption, lack of physical activity, lack of medical care, irregular use of medication and much more. "All these factors usually have a hundredfold stronger effect" than the increased risk from air pollutants, writes Köhler and his co-signatories.

Last but not least, the epidemiological studies completely ignore the question of a toxicological threshold dose for the respective air pollutant, the author posits, although "every poison, even the strongest, has a threshold dose."

More about that debate: How many people die from air or noise pollution?

Battling air pollution through driving bans

Too much traffic makes for bad air

Cities all over the world are fighting against smog. A German court has ruled that cities are allowed to impose driving bans. Many German cities — including Stuttgart, shown here — have developed an air pollution problem and are debating how best to approach the problem.

Battling air pollution through driving bans

Oslo, where the diesel ban is reality

A diesel ban is imposed in the Norwegian capital whenever air pollution levels rise above a prescribed limit. The ban went into effect for the first time on January 17, 2017. Ambulances and other public service vehicles running on diesel are exempt from the measure. The city plans to reduce even more cars by eliminating municipal parking spaces in the center starting in 2019.

Battling air pollution through driving bans

Paris is also planning a diesel ban

Starting in 2024, the French capital will ban diesel vehicles; in 2030 it intends to expand the ban to gas-powered cars. Vehicles manufactured before 1997 are already prohibited in the city on weekdays. When air pollution levels exceed prescribed limits, Parisians have to follow a rotation system in which only cars with either even- or odd-numbered plates are allowed to be driven in the city.

Battling air pollution through driving bans

London has a congestion charge

If you want to drive into the center of London, a day's ride through the city will cost you 10 pounds ($13.80, €11.20). London introduced the congestion charge in 2003. Automatic number plate recognition is used to enforce the measures. Anyone who does not pay the fee faces a heavy fine of up to 240 pounds.

Battling air pollution through driving bans

Copenhagen – the most bike-friendly city in the world

Copenhagen's mayor, Frank Jensen, wants to prevent new diesel cars from entering the city starting in 2019. Currently, over 300 kilometers of roads in the Danish capital can only be used by cyclists. With the new regulations, cycling will become easier, more convenient and cheaper than driving a car. About half of Copenhageners now cycle to work.

Battling air pollution through driving bans

Pedestrian zones spreading in Madrid

Car-free zones like the square in front of Madrid's Teatro Real are set to become a common sight in the city. Almost the entire center of the Spanish capital will be turned into pedestrian zones in the next five years. Madrid has high smog levels, due to being surrounded by mountains, which cause bad air to get trapped in the city.

Battling air pollution through driving bans

Helsinki offers a traffic app

Riding public transport will become even easier in the near future in Helsinki. In the next ten years, a mobility on demand system will be developed to include all forms of public transport in one app, including buses, self-driving cars and minibuses with flexible routes. The goal of the app is to be so good that no one will want to own a car.

Battling air pollution through driving bans

Driving electric rickshaws in Delhi

Smog chokes Delhi and levels of air pollution regularly go off the scale. Electric rickshaws will hopefully alleviate the problem. By 2030, all new vehicles will be electrically powered and the city will phase out gas powered vehicles.

Many victims of smoking, but where are the NOx deaths?

Should there actually be many causal deaths from particulate matter and NOx, then lung doctors should notice this in their daily practice, Köhler argues. But this is not the case at all.

Köhler cites an epidemiological study commissioned by Germany's Federal Environment Agency (UBA) as an example. This study calculates additional deaths per year for NOx at 6,000 - 13,000 and for particulate matter at 60,000 - 80,000. That would be about as many people as dying a result of smoking.

"In their practices and clinics, pulmonary physicians see [deaths caused by cigarette smoke] on a daily basis; however, deaths caused by particulate matter and NOx, even after careful investigation, never," write the pulmonary physicians in their counterposition.

So it is "very likely" that the scientific data leading to these estimates "contains a systematic error." Apparently, they have been "interpreted extremely one-sidedly" and "always with the objective that particulate matter and NOx must be harmful," they write. 

Appeal for a fair and open discussion

Köhler and his colleagues see their paper as helping to bring more objectivity to the emotional debate about driving bans, pollution limits and diesel exhaust gases. At least here they agree with the representatives of the established associations of pulmonary physicians.

The DGP, the Association of Pneumological Clinics (VPK), and the German Lung Foundation regard the publication "as an impetus for necessary research activities and a critical examination of the effects of nitrogen oxides and particulate matter," write the respective chairmen of the three associations Klaus F. Rabe, Thomas Voshaar and Claus Vogelmeier in a joint press release. 

Delhi is choking in smog


As the nations of the world discuss strategies to reduce emissions at COP23 in Bonn, on the other side of the world, thick smog has engulfed the Indian capital Delhi.

Delhi is choking in smog

Worst air champion

Smog is quite common in Delhi. In fact, the city on the Yamuna river is a sad record holder: it is the capital city with the worst air quality in the world.

Delhi is choking in smog

Winter makes things worse

While the advent of winter doesn't bring snow in Delhi, it habitually makes conditions worse in the megacity. That's because the cooler air traps the smog close to the ground.

Delhi is choking in smog

That damn traffic!

An important contributor to smog is usually motorized traffic, which holds true for Delhi as well. Beyond that, farmers in nearby rural areas traditionally burn their fields after harvest, thereby making their own contribution to air pollution. This practice is technically banned but authorities tend to turn a blind eye.

Delhi is choking in smog

The festival of light

This year, Diwali added to the pollution. The Hindu festival of light not only brought a lot of traffic to the city, it also involved burning large amounts of firecrackers. And it goes on for five days!

Delhi is choking in smog

Can't breathe, can't see

The smog in the city has gotten so thick that it has become difficult to breathe. It burns the eyes and throat and many people complain of headaches. It even obscures the sun.

Delhi is choking in smog

Face mask

People try to protect themselves against the fine particle pollution as best they can using scarves and face masks. But there is really no escaping it.

Delhi is choking in smog

More than a little too high

On Wednesday, pollution levels in the city reached almost 30 times those considered safe by the World Health Organization.

Delhi is choking in smog

Pollution, the great equalizer?

Even heads of state can't escape the thick air. The Belgian King Philippe, inspecting a military guard of honor during his state visit to Delhi is shrouded in smog just like everyone else.

Delhi is choking in smog

Cheap fares and expensive parking

In a first measure to reduce pollution, the city government has targeted motorized transportation. By lowering fares on public transport and raising the fees for parking, it hopes to keep people from driving.

Delhi is choking in smog

No school this week

The chocking smog has also led the city to shut all schools for the remainder of the week.

Delhi is choking in smog

Protesting pollution

People in Delhi are fed up with the chronically bad air quality in their city. These women wearing face masks are on their way to a protest. So far, the city's response to the crisis has been half-hearted at best.

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