I have written before about air pollution and pollution peaks . Let us now focus on nitrogen dioxide (NO2) which is quite possibly the most harmful of all gases. I believe that a deeper understanding of air pollution should facilitate a faster change in mentalities. What is this gas that is so damaging to our environment and our bodies?
What is nitrogen dioxide?
Nitrogen dioxide is a member of the nitrogen oxide family. Its two constituents, nitrogen dioxide and nitric oxide, are the main air pollutants on earth.
It serves as a precursor to various hazardous secondary pollutants, including ozone and fine particles.
Because we can see and smell it, NO2 gas is easy to identify. In fact, it can be identified by its reddish-brown color and its strong, distinctive odor. It is a foul smell that is usually present in heavily congested streets.
How is nitrogen dioxide created?
Concretely, it is the transformation of nitrogen, which constitutes 80% of the air we breathe, which is at the origin of NO2. This nitrogen will oxidize at high temperature and transform into nitrogen dioxide gas when it comes into contact with oxygen.
Internal combustion in car engines – mainly diesel engines – and thermal power plants are the main sources of this gas. Therefore, the main culprits are industry and cars.
This was clearly highlighted (as below in China) during the 2020 lockdowns, when teleworking prevented workers from using their cars.
How is nitrogen dioxide measured?
Air Quality Index (AQI) determines whether our atmosphere is polluted. It's calculated by taking into account measurements of the six main pollutants, including PM10 and PM2.5 particles, and especially NO2, which is the most frequent air pollutant in this index.
There are many applications to monitor pollution levels in most major cities of the world.
Where is NO2 pollution most prevalent?
We know that cars are the main culprits and that road traffic produces the largest quantities. Therefore, people who live near jammed roads are the most affected by this air pollution. If you have domestic appliances running on gas, you may also be exposed. These include appliances such as gas and oil boilers, as well as water heaters. If you smoke, you may also be exposed to it at home, as cigarette smoke also contains NO2.
There is no doubt that this gas is toxic to humans. What is more unexpected is that it is dangerous for individuals but also for the environment.
The environmental effects of nitrogen dioxide?
The rust-colored toxic gas nitric acid is created from nitrogen dioxide once it is in the atmosphere and then falls to the ground, especially on vegetation. This mechanism contributes to the development of acid rain as well as the acidity of lakes and soils. Nitric acid, which is produced when NO2 is converted, can also corrode metals and stain fabrics and stone of buildings.
Nitrogen dioxide seriously damages plants and crops, causing nutrient pollution, so some traces of it can end up in our food.
Is nitrogen dioxide dangerous for humans?
NOx in general, including nitrogen dioxide, can harm our respiratory systems. In fact, this gas will have the most serious respiratory impacts because of its extremely small size. Its toxicity will make respiratory problems more likely in people who are already vulnerable, such as young people and people with asthma. Children are particularly vulnerable because they breathe more rapidly than adults, and because they are smaller, and therefore closer to vehicle exhausts.
Cases of high exposure, such as during pollution peaks, can lead to acute respiratory poisoning, which manifests itself as coughing, dyspnea (difficulty breathing) and haemoptysis (blood produced when coughing). Finally, all malignant lung tumours that are not linked to smoking are linked to ambient air pollution.
A recent large study found evidence that NO2, ozone, and other airborn pollutants increase the risk of lung cancer in humans. This 2016 study tracked the air pollution levels to which more than 350,000 cancer patients were exposed between 1988 and 2011 in California. The researchers found that their survival was reduced by exposure to these air contaminants.
Beyond the lungs, more recent studies have linked NO2 to cardiovascular damage, lower newborn weights and an increased risk of premature mortality.
What are the WHO recommendations?
The World Health Organization and European guidelines agree that the annual average concentration of NO2 should not exceed 40 g/m3. Similarly, the hourly average concentration is limited to 200 g/m3.
Exceeding the WHO recommended limits of g/m3 poses a risk to human health whether as an hourly or annual average.
What is being done to reduce NO2 pollution?
Using low-nitrogen fuels is an interesting option to reduce NOx emissions. Another one is to modify the combustion process to produce less NOx. NOx can be removed using flue gas treatment methods, including Selective Catalytic Reduction (SCR) technologies.
In developed countries, nitrogen dioxide concentration levels are decreasing every year thanks to:
- The expansion of public transports
- More efficient and "greener" car engines
- Reducing speed limits on motorways and downtown
- The development of hydrogen/electric engines for trucks and buses
- The expansion of hybrid and electric cars
- To the incredible explosion of bike commuting
This is reflected in this graph, which shows the radical fall in nitrogen dioxide levels in the UK between 1998 and 2020.
Do anti-pollution masks protect from nitrogen dioxide?
More and more people are concerned about this issue when air quality deteriorates, for example during episodes of pollution peak, and seek to protect themselves.
They can then use a anti-pollution mask.
Two crucial criteria must be taken into consideration:
- Efficiency: What contaminants and at what particle size will my mask filter?
- Will inhaled air get through filters? Is it airtight enough?
That's why I created Frogmask anti-pollution masks which precisely meet these two requirements:
- They filter at least 94% of inhaled airborn particles up to 0.4µm thanks to FFP2/N95 filters.
- Frogmask is one of the few brands proposing 3 different sizes (M, L and XL) because one size fits all is a complete nonsense. How can one size of mask fit all face sizes and shapes?
