In getting caught in a cheating scandal, Volkswagen was called out for emitting 10-40 times the legal limit of nitrogen oxides, or NOx.

In short, nitrogen oxides are toxic gases produced under high pressure in the engine by combining nitrogen and oxygen.

SEE ALSO: What Volkswagen’s ‘Dieselgate’ Is, and Why it Matters

NOx may cause myriad adverse effects to the environment and human health, and derivatives of the family of nitrogen oxides include nitrogen dioxide, nitric acid, nitrous oxide, nitrates, and nitric oxide.


NOx has been linked to smog and acid rain which harm plant and animal life; the land and the water.

Acid in the environment may also come down not just as “rain” but as fog, snow, or dry particles.

It can travel hundreds of miles on the winds, and acid damage surfaces it comes in contact with, including to buildings, cars, monuments, and more.

Early morning emissions in London. © Simon Birkett 2014.

Early morning emissions in London. © Simon Birkett 2014.

As for smog, this is not desirable anywhere, but California has long raised a flag against any threat to its air quality. Its Air Resources Board once got its charter in large part because of dense blankets of smog that characterized its regions.

Authorities in the U.S. and Europe are still combating NOx which comes predominantly from human technologies such as the engines that drive vehicles and equipment.

In the air, NOx may form nitric acid and related particles by reacting with ammonia, moisture, or other compounds.

SEE ALSO: How Volkswagen Tricked the EPA’s Emissions Test

It can contaminate and deteriorate water quality in lakes and streams and oceans by nitrogen loading.

The Chesapeake Bay is currently under siege by nitrogen pollution, as one example. A condition leading to oxygen depletion called eutrophication can diminish the population of fish and shelfish.

Last but not least, NOx is a greenhouse gas, leading to global warming and climate change.

Human Health

NOx is made up of nitric oxide (NO) and poisonous nitrogen dioxide (NO2) in smaller quantities.

In the atmosphere, NOx reacts with organic compounds and ozone.


It has been linked to childhood asthma, as well as asthma in all ages. Asthma from the environment can be like a stimulus-response event. A “trigger” including smog can induce a person’s lungs to go into spasms which have been conditioned to be more sensitive in the asthmatic.

Other issues may include loss of appetite, tooth corrosion, genetic mutations, vision impairment or eye irritation, and headaches.

SEE ALSO: VW CEO Winterkorn Resigns As Emission Scandal Unfolds

Obviously different people react with varying levels of tolerance. People living in clustered areas, such as cities and near highways are more susceptible because of the higher concentrations of the exhaust of internal combustion vehicles.


NOx emissions are a byproduct of combustion accepted nearly as a necessary evil. Society has long-since been set up to function on the backbone of the internal combustion engine, and more-efficient diesels do much of the product transport and heavy work.

Today most diesel passenger vehicle manufacturers employ urea injection – also known as diesel exhaust fluid – to reduce NOx to legal levels set by the EPA’s tier 2, bin 5 standards.

Authorities take NOx so seriously, this diesel exhaust fluid – filled about the same intervals as an oil change – must always be maintained and present in the vehicle. If a car or truck runs out, it goes into a severely handicapped limp-home mode.

VW had promoted its “clean diesel” tech from 2009 onward as an amazing engineering feat that passed tests without urea injection. It was cheaper to produce, and made for a simpler car and owner experience.

Its cars also performed like champs, beating the EPA mpg oftentimes with stump-pulling torque, all while touted as “green.”

Ironically Volkswagen’s issues came to a head just when it had rolled out 2.0-liter diesel engines this model year with urea injection that might have let them make the grade.

The 2009-2014 EA188/189 U.S./EU spec engines in question are for now the only named culprit, though the new EA288 in 2015 Golf, Jetta, Passat, Beetle, and Audi A3 models was also culled.

Apparently the “defeat device” was left in place for the EA288 but even if it had been able to pass emissions without it, 11 million pieces of evidence were also left in place in the hands of owners around the world.

A fix for VW’s NOx problem has yet to be announced.