What is NO2 gas (nitrogen dioxide)?

Welcome to our complete file on air pollution, with today a focus on nitrogen dioxide NO2.

At R-PUR, we are convinced that a global understanding of air pollution would make it possible to change mentalities more quickly.

We therefore have at heart to explain simply what is this visible and odorous gas which does a lot of damage to our organism.

You can also find our dedicated article on the air quality index , which will explain why this tool is essential for your health.

What is Nitrogen Dioxide? Definition and measurement.

Called nitrogen dioxide, No2 is part of the family of nitrogen oxides, No. Its two members, nitrogen monoxide and dioxide, are the major pollutants of the Earth's atmosphere.

It is a precursor to many harmful secondary pollutants, such as ozone and fine particles.

NO2 is defined by its chemical composition, No 2.

NO2 gas is easily recognizable since it is visible and smells.

Indeed, it is recognized by its reddish-brown color and its characteristic acrid and pungent smell.

It is an odor that is typically found in streets polluted by automobile traffic.

Since, between you and us, the diagrams of atoms that we see in chemistry in college are not very telling, here is what the gas No2 really looks like:

On a daily basis, to determine whether the atmosphere is polluted, we rely on the AQI, which is the Air Quality Index.

The AQI is calculated by taking into account the measurements of the six main pollutants, including PM10 and PM2.5 in particular: NO2 is the most polluting gas in this index.

Where does NO2 gas come from?

Let's start first with a theoretical approach.

Concretely, the formation of No2 in chemistry results from a transformation of the nitrogen present in the air (nitrogen represents 80% of the air that we breathe).

This nitrogen, under high temperatures, will oxidize and, in contact with oxygen, will turn into No2 gas.

In practice, this gas is mainly produced by internal combustion engines (largely diesel) and thermal power stations.

Cars and industries are therefore the biggest culprits.

The No2 is therefore not innocent of the fact that road traffic is often polluted, particularly at rush hour. The latter also largely contributes to the formation of smog (cloud of pollution).

Moreover, the AirParif organization is carrying out its 5th edition of the car-free day in the Paris region in 2019 in order to observe the correlation between nitrogen dioxide and urban traffic.

The most marked decrease was -45%, on average over the duration of the device, so over one day.

Thanks to this study, we know the correlation between road traffic and the concentration of No2 in the air. There are, however, other less suspected NO2 exposure sites.

Where are we most exposed to NO2 pollution?

We therefore now know that the main culprits are cars, and that the highest concentrations are observed in road traffic.

Thus, it is the populations living near major highways that suffer the most from pollution.

You can also be exposed to pollution at home, if you have gas-powered household appliances.

We are talking here about appliances such as gas stoves, water heaters and oil stoves.

You can also be exposed to it from home if you are a smoker: No2 is also produced by cigarette smoke.

You will not doubt it, this gas is therefore toxic. What is more surprising is that this gas is not only toxic to humans, but also to our environment.

What are the dangers for nature?

The toxic red-brown gas No2 not only poses dangers to humans but also to our environment.

Indeed, once in the atmosphere, the nitrogen dioxide will be transformed into nitric acid which will fall to the ground and in particular on the vegetation.

This process will contribute to the acidification of soils and lakes, and to the formation of acid rain.

No2 transformed into nitric acid can also damage metals by corroding them and clothing by discoloring the fabric.

Nitrogen dioxide, ultimately, causes heavy losses to trees and crops, and even to our buildings.

The consequences are such that certain monuments known to all, such as the Taj Mahal , are damaged.

This phenomenon is explained by the fact that acid rain will not only yellow and tarnish the facade of buildings, but also by eroding the stone, starting with the most fragile sculptures.

Another well-known example is the Colosseum in Italy.

The dioxide therefore weakens buildings, metals, trees: we can then wonder what is happening to our lungs.

Is nitrogen dioxide dangerous for health?

Nitrogen dioxide and NO in general can deteriorate our respiratory conditions.

Indeed, due to its very small size, this gas will penetrate into the finest respiratory ramifications.

Its toxicity will promote respiratory problems in already fragile people, such as asthmatics, and children.

Children are all the more affected because they breathe faster than adults, combined with the fact that they are smaller, lower, and therefore closer to car exhausts.

Significant cases of exposure can cause acute respiratory tract poisoning such as coughing, dyspnea (respiratory discomfort), and hemoptysis (blood discharge during coughing).

Finally, according to Olivier Blond , president of the Respire association, all lung cancers that are not linked to cigarettes are linked to ambient air pollution.

When we know that the smoke of diesel vehicles contains the same toxic gases as cigarettes, such as No2, this observation seems obvious.

We now know that an exhibition in an urban environment is now almost inevitable.

We also know the effects of No2 on health, in the event of more or less significant exposure.

Now let's see how we should regulate this exposure, with concrete figures to back it up.

What does the World Health Organization (WHO) recommend?

European directives are in agreement with the World Health Organization on this point: the average annual concentration of NO2 should not exceed 40 µg/m3.

The aim is to protect public health.

In this sense, there is also an hourly average concentration limit: this is 200 µg/m3.

Whether on an hourly or annual average, exceeding the µg/m3 limits recommended by the WHO will represent a danger to human health.

How to protect yourself from it? What about anti-pollution masks?

When the air quality is poor, such as during episodes of pollution or pollen , more and more people affected by the problem seek to protect themselves.

They can then turn to an anti-pollution mask. It is then necessary to take into account two essential parameters:

Efficiency : what pollutants will my mask filter, and up to what size?

Hermeticity: in other words, will the outside air enter my mask?

For example, if 40% of the air were to enter your mask, which is the most effective in the world, there would not be much point in wearing it in the middle of road traffic.

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