What is nitrogen oxide and how do cars create it?
Car pollution isn’t all about carbon dioxide. Before 2015, a low-emission car was simply one that produced a low volume of carbon dioxide – the pollutant was seen as the major concern, so others weren’t given as much focus.
However, in 2015, car manufacturer Volkswagen found itself at the heart of a scandal known as “dieselgate”. The manufacturer was caught red-handed intentionally using emissions controls during laboratory testing only, meaning its cars produced up to 40 times more nitrogen oxide in actual driving than reported.
This put nitrogen oxide, and its damaging effects on public health, into the limelight. Now, carbon dioxide isn’t the only emission car manufacturers need to control.
Why is nitrogen oxide pollution so dangerous, how do cars produce it, what are its effects and why are car manufacturers so concerned about it? We’ll tell you all the car pollution facts you need to know, below.
What is nitrogen oxide and how do cars produce it?
Nitrogen oxide in cars is nothing new. Airborne nitrogen, in isolation, isn’t harmful to humans. It makes up 80% of our atmosphere, but it becomes particularly troublesome when it becomes bonded with another element: oxygen.
So, how are nitrogen oxides produced and formed? When a car engine runs, it causes combustion by heating up quickly. This process acts as a catalyst which binds together nitrogen (N) and oxygen (O2) to form nitric oxide (NO) or nitrogen dioxide (NO2). Both are described generically as nitrogen oxide (NOx). This isn’t the intended result, so nitrogen oxide is just a by-product.
In sterile lab conditions, pure combustion uses hydrocarbons (gasoline, diesel, etc.) and oxygen to produce carbon dioxide and water. The world, however, isn’t a lab, and car manufacturers need to factor in and reduce the production of unwanted by-products.
Nitrogen oxide in car engines, explained
One key aspect of achieving more power through a car engine is to produce more oxygen. More oxygen allows gas to burn even quicker, which results in more power. The cylinders used within car engines can only hold so much oxygen, to which a process called ‘forced induction’ acts as a potential cure via turbochargers.
Turbochargers act much like engine pistons, in the sense that they push even more air into oxygen cylinders. This results in a higher volume of fuel combustion and, subsequently, produces more power.
However, there is one other way of injecting even more oxygen into a cylinder using nitrous oxide. Nitrous oxide is a gas that was discovered in the late 1700s and it was primarily used for medical reasons like pain relief.
In the motoring industry, nitrous oxide is more commonly referred to as ‘NOS’. NOS stands for ‘Nitrous Oxide System’, a process by which nitrous oxide is used within a car to push more oxygen into the cylinder. As shown by movies like Fast and Furious, the nitrous gas is kept within a cannister and connected to the car’s fuel delivery system. When the driver wishes to use the nitrous for an increased jolt of speed, they simply press a button that releases the nitrous oxide into their engine.
It is important, however, to remember the difference between nitrogen oxide and nitrous oxide. Nitrogen is an element made from two nitrogen atoms (N2), whereas nitrous oxide is a chemical compound made of two nitrogen molecules and one oxygen molecule (N2O).
The negative effects of nitrogen oxide
If nitrogen oxide was harmless, then there wouldn’t be any problems. Even if the effects were small, there wouldn’t be as much widespread concern over its production.
Nitrogen oxide pollution, however, has profound negative effects on public health. In the UK, the Committee on the Medical Effects of Air Pollutants has stated that “studies of long-term exposure to NO2 report associations with all-cause, respiratory and cardiovascular mortality, children’s respiratory symptoms and lung function.”
For those who live in urban and metropolitan areas, this exposure to nitrogen oxide is high. Some of the short-term and long-term consequences of the pollutant include:
- Nausea
- Difficulty breathing
- Coughing
- Aggravation of respiratory diseases
- Asthma
- Infection
- Links to decreased fertility
There is a range of other diseases that have had a causal link to nitrogen oxide, too. As you can see from just this shortlist, the side effects of NOx emissions from cars is a cause of concern for manufacturers, city councils and governments.
What type of fuel produces more nitrogen oxide?
When it comes to buying a car, you may want to consider the environmental consequences of your purchase.
While diesel engines tend to have better fuel efficiency, it comes at a cost. You may expect diesel to win the NOx emissions diesel vs gasoline fight, but the result is the opposite.
Better efficiency means diesel engines operate at a higher temperature and pressure than their petrol counterparts. This increases the volatility of combustion, leading to the production of stronger, more abundant nitrogen oxide.
Petrol engines still produce nitrogen oxide, but not to the same volume as diesel engines. This doesn’t mean petrol engines don’t need to be modernised and changed, as the volume they produce can still be a threat to public health.
Do older cars produce more nitrogen oxide?
By and large, yes. Newer models have made an effort to reduce the production of nitrogen oxide, with these models producing more carbon dioxide than older versions to compensate.
While newer cars may produce more carbon dioxide than older vehicles, they produce considerably less carbon monoxide and nitrogen oxide. The increase in carbon dioxide is minimal, too, compared to the much larger decrease in other pollutants.
For modern cars, it’s better to have a slight increase in carbon dioxide production if it means harmful gases are reduced.
How to reduce nitrogen oxide emissions in cars?
With the negative effects of nitrogen oxide well documented, car manufacturers have been on the hunt for ways to reduce its presence in modern vehicles. Here’s how to reduce NOX emissions in cars:
Euro emission standards
The Euro emissions standards are a set of rules that all car manufacturers must comply with that dictate the maximum number of emissions that a car can legally produce. First introduced in 1992 alongside the mandatory inclusion of catalytic converters, these standards have played a crucial role in reducing the number of emissions that our cars produce.
Statistics show that as of 2017, nitrogen oxide emissions are down 84% as a result of these rules since 2001.
Real driving emissions
To further optimise the number of emissions that our cars produce, an additional metric has been introduced to the Euro emissions standards.
From September 2017 onwards, cars must undergo a series of tests to ensure that they meet any new standards in actual driving circumstances. Real Driving Emissions (RDE) tests shall include a mixture of regular and motorway driving to determine how a car performs in the real world. This will push manufacturers to focus on the real-world effects of their emission reduction, instead of focusing on synthetic benchmarks.
Exhaust gas recirculation
One critical way in which nitrogen oxide emissions is reduced in cars is through the use of exhaust gas recirculation (EGR). In a process like condensing boilers, EGR uses exhaust gas from a car’s engine and rediverts it back into the engine cylinder.
This effectively reduces both the amount of oxygen in the cylinder and the temperature of the cylinder to help produce fewer volatile emissions.
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