Air quality around the world is poor - according to the World Health Organization (WHO), more than 90 percent of the earth's inhabitants suffer as a result.
About 3 million people die from outdoor dirty air each year - the European Environment Agency estimates that some 430,000 Europeans die prematurely each year as a result.
Traffic plays a major role, especially in cities. This is due above all to deadly particulate matter generated by tire, brake and street abrasion. Traffic also kicks up a lot of dust. And lastly, internal combustion engines generate large quantities of fine particles.
"Many major studies, some of which included hundreds of thousands of participants, have shown that fine matter particles and diesel soot lead to health problems, including cardiovascular illnesses - such as heart attack and stroke, lung disease, diabetes, low birth weights among newborns and asthma in young children," explained Barbara Hoffmann, who heads the department of environmental epidemiology at the University of Düsseldorf Hospital.
"Furthermore, diesel soot contains carcinogens that can lead to lung cancer. These health threats are very well-documented - one can generally state that every 1 microgram increase in fine matter in the air increases the number of certain illnesses," Hoffmann told DW.
The WHO suggests a maximum of 20 micrograms of particulates, designated PM10 (or 10 micrometers in diameter), per cubic meter of air.
According to Germany's Federal Environment Agency (UBA), that number is regularly exceeded at more than a quarter of all the agency's measuring stations throughout the country. Nevertheless, modern filtering techniques installed in most new cars have led to a vast improvement over past levels.
The WHO, however, says that air in many cities around the world is much worse than in countries like Germany and the United States. Beyond old cars and trucks, much of that pollution is caused by coal-fired power plants, factories and open fires.
Automakers violate health protection requirements
Another health threat comes from nitrogen oxides (NOx). In Europe, 40 percent of that poisonous gas is emitted from diesel motors, next to about 20 percent each by power plants and industry.
Nitrogen oxides cause two major problems. Firstly, they reacts in the atmosphere to create more fine particle matter; and secondly, the gas directly attacks the respiratory system.
"People with preexisting respiratory illnesses are the most greatly affected," says Hoffmann. "Such acute stress to their system can cause serious damage to their health." Moreover, studies show that long-term exposure decreases life expectancy and increases the likelihood of cardiovascular disease, she added.
The European Environment Agency estimates that 75,000 Europeans died prematurely as a result of nitrogen oxide poisoning in 2012 - among them 22,000 in Italy, 14,000 in Great Britain and 10,000 in Germany.
In an attempt to protect the health of EU citizens, nitrogen oxide emissions limits have been established across Europe. Since 2010, that limit has been set at an annual maximum of 40 micrograms of NOx per cubic meter. Beyond that, all automobiles produced after January 2000 have been required to meet NOx emission reduction standards.
Yet automakers have shamelessly flouted such emissions and health protection standards. Automobiles were equipped with software designed to trick laboratory ratings tests, and in normal driving conditions emissions far exceeded legal limits.
The discovery of this systematic criminal behavior in September 2015 eventually led to the so-called "dieselgate" emissions scandal.
According to the Federal Environment Agency, the newest diesel cars (category Euro 6) on German streets are emitting an average of six times more NOx than is allowed by law; older cars (Euro 5) emit five times as much, and (Euro 4) three times as much as is allowed.
Unnecessary deaths due to inadequate emission controls
The UBA says that average NOx limits were exceeded at some 57 percent of all air quality measuring stations installed near German streets last year.
"In the cities, old diesel automobiles are clearly to blame," said UBA President Maria Krautzberger when presenting the data. "As a matter of public health, it is simply unacceptable that municipalities have no tools at their disposal to allow them to ban soot-producing diesel cars from entering their cities."
"Ultimately, we are talking about protecting the health of our citizens."
The effects of worldwide emissions manipulations by the automobile industry have been documented in a study recently published by the trade journal "Nature." For the project, an international team, under the leadership of the International Council on Clean Transportation (ICCT) and Environmental Health Analytics, evaluated more than 30 studies on diesel emissions, air pollution and disease.
Researchers concluded that some 107,600 premature deaths were directly related to air pollution caused by nitrogen oxide emissions from diesel motors in the most automobile-intensive regions of the world in 2015.
Researchers estimate that roughly 38,000 people died as a result of automobiles exceeding legal emissions standards. Around 28,000 people died as a result of buses and trucks exceeding those limits, and a further 10,000 as a result of cars doing the same.
Diesel emission controls easily applied
Auto industry and environmental experts agree that emission controls can be easily applied when it comes to diesel motors - that is, if effective catalytic converters are correctly installed and not programmed to cut out when in use in traffic.
Emissions measurements conducted by the nongovernmental organization German Environmental Aid (DUH) found that Mercedes and Audi cars (both Euro 6) currently emit far less than regulatory limits.
A new study by ICCT also found that so-called selective catalytic reduction (SCR) functions so well on new buses and large trucks that these emit far less nitrogen oxide than most new diesel cars (all Euro 6).
SCR catalytic converters use urea (German brand-name AdBlue) as an additive in the car's fuel. The technique is also used to scrub emissions at large industrial facilities, such as waste incinerators.
Dirty air is expensive
Health, environment and consumer experts, as well as lawyers and a growing number of politicians, have increasingly been calling for automakers to retrofit diesel vehicles at their own cost. They say that complying with legal emissions standards for cars and trucks fulfills citizens' rights to clean air and good health in European cities.
So far, the automobile industry has balked at the idea of footing the bill for what is, in fact, its own responsibility. The German government has neglected to apply sufficient pressure on domestic automobile manufacturers to this end, as well.
According to emissions expert Axel Friedrich, most cars could be sufficiently retrofitted for an average price of 1,500 euros ($1,750) per vehicle. This retrofitting would put the vehicles in compliance with emissions standards.
Many see this as a small price to pay in light of the health and economic damage caused by such emissions.
In environmental epidemiologist Hoffmann's view, the one thing that has been missing in the diesel debate has been any reference to the societal costs that dirty diesel emissions generate.
Many people have no idea of the effects of air pollutionm, she says: "If you calculate what premature deaths and additional illnesses alone really mean in terms of costs, then you quickly realize how relevant the topic is in societal terms - and what an enormous financial burden it is."
"Then, perhaps people would also see that investing in cleaner air is really worth it."