Welcome to our complete report 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 are therefore keen to explain simply what this visible and odorous gas is which does a lot of damage to our body.
You can also find our complete file to easily understand air pollution .
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, constitute the major pollutants of the earth's atmosphere.
It is a precursor to many harmful secondary pollutants, such as ozone and fine particulate matter.
NO2 is defined by its chemical composition, No. 2.
NO2 gas is easily recognizable since it is visible and odorous.
Indeed, it is recognized by its red-brown color and its characteristic pungent and pungent odor.
It is a smell typically found in streets polluted by car traffic.
Since, between you and us, the atom diagrams that we see in middle school chemistry are not very meaningful, here is what No2 gas actually looks like:
On a daily basis, to determine whether the atmosphere is polluted, we base ourselves 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 we breathe).
This nitrogen, under high temperatures, will oxidize and, on contact with oxygen, transform into No2 gas.
In practice, this gas is mainly produced by internal combustion engines (largely diesel) and thermal power plants.
Cars and industries are therefore the biggest culprits.
No2 is therefore not innocent of the fact that road traffic is often polluted, particularly during rush hours. The latter also contributes largely 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 reduction was -45%, on average over the duration of the system, therefore over one day.
Thanks to this study, we know the correlation between road traffic and the concentration of No2 in the air. However, there are other less suspected places of exposure to NO2.
Where are we most exposed to NO2 pollution?
We now know that the main culprits are cars, and that the highest concentrations are observed in road traffic.
Thus, it is the populations who live near major roads who suffer the most from pollution.
You can also be exposed to pollution at home if you have household appliances that run on gas.
We are talking here about devices such as gas cookers, water heaters and kerosene stoves.
You can also be exposed to it from home if you are a smoker: No2 is also produced by cigarette smoke.
You will have no doubt, 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 poses dangers not only to humans but also to our environment.
Indeed, once in the atmosphere, nitrogen dioxide will transform into nitric acid which will fall to the ground and in particular on 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 erode the stone, starting with the most fragile sculptures.
An equally well-known example is the Colosseum in Italy.
Dioxide therefore weakens buildings, metals, trees: we can then wonder what is happening to our lungs.
Is nitrogen dioxide dangerous for your health?
Nitrogen dioxide and No in general can deteriorate our respiratory conditions.
Indeed, due to its very small size, this gas will penetrate the finest respiratory branches.
Its toxicity will promote respiratory problems in people who are already fragile, such as asthmatics, and children.
Children are even more affected because they breathe faster than adults, combined with the fact that they are smaller, lower, and therefore closer to car exhaust pipes.
Significant cases of exposure can cause acute respiratory system poisoning such as coughing, dyspnea (respiratory discomfort), and hemoptysis (discharge of blood 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 from diesel vehicles contains the same toxic gases as cigarettes, such as No2, this observation seems obvious.
We now know that exposure 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 support it.
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 objective 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 limits of µg/m3 recommended by the WHO will represent a danger to human health.
How to protect yourself from it? What about anti-pollution masks?
When air quality is not good, 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. Two essential parameters must then be taken into account:
Efficiency : what pollutants will my mask filter, and to what size?
Hermeticity: in other words, will outside air enter my mask?
For example, if 40% of the air were to enter your mask, which is the most efficient in the world, there would not be much point in wearing it in the middle of road traffic.