An introduction to nitrogen dioxide air pollution

Air pollution is the largest environmental health risk in Europe, causing cardiovascular and respiratory diseases, contributing to poor health and even premature death. There are multiple factors that contribute to poor air quality such as PM2.5, formaldehyde, and nitrogen dioxide, which by Dr. Chunli Cao, CEO of Healthy Air Technology, examines in this article.

photograph of sky

Nitrogen dioxide (NO2) is caused by road transport, which emits NO2 close to the ground. It’s primarily concentrated in densely populated areas, resulting in population exposure. Other important contributors of NO2 are combustion processes in industry and the energy supply. In Europe, the highest concentrations were found in large cities with high traffic volumes.

The maps show the number of years of life lost per country attributable to air pollution (PM2.5 left and NO2 right).

What is Nitrogen Dioxide exactly?

Nitrogen oxides are common air pollutants, usually referring to nitrogen monoxide and nitrogen dioxide, often expressed as NOX. Nitric oxide is a colorless, odorless gas that quickly turns into nitrogen dioxide in the air. Therefore, it is mainly nitrogen dioxide that exists in the air for a long time and poses a threat to human health.

Nitrogen dioxide is corrosive, highly oxidizing, and easily soluble in water. Under the action of sunlight, nitrous acid and nitric acid can be formed. Nitrogen dioxide rapidly destroys lung cells, which can lead to emphysema and pneumonia, causing acute asthma.

Nitrogen dioxide in the atmosphere undergoes a series of chemical reactions to form nitric acid, which becomes a component of acid rain. With the increase of the number of motor vehicles in cities, the proportion of nitric acid in acid rain continues to rise. Nitrogen dioxide is also one of the main pollutants that cause urban photochemical smog pollution.

High-temperature combustion is the main source of nitrogen dioxide at low altitudes. Vehicle exhaust, boiler combustion, and kitchen fume emissions will all produce nitrogen dioxide. Nitrogen dioxide in the atmosphere will enter the room through leaks in buildings, open doors and windows and ventilation systems.

To further reduce global public health risks, the World Health Organization (WHO) revised released the “Global Air Quality Guidance Values (2021)” (AQG 2021). The guideline document proposes the guideline value levels (AQG) of six major air pollutants including NO 2, based on the results of scientific research to determine the minimum concentration value of air pollution at which people are exposed to air pollution and cause health risks.

The AQG applies to both indoor and outdoor environments and based on new evidence of the association between long-term NO 2 exposure and all-cause and respiratory disease mortality, the AQG changed the annual mean target for NO 2 from 40 µg/m³ to 10 µg/m³; The daily average target value is 25µg/m 3.

AQG is mainly aimed at infants, susceptible populations with cardiopulmonary and metabolic diseases and other diseases related to air pollution exposure. Many studies have revealed that for countries and regions with relatively serious air pollution (including China), the air pollution standards formulated according to the old WHO AQG have limited health protection effects on susceptible populations, and more stringent AQG will better protect vulnerable populations. Infected people are protected from the effects of air pollution.

An air purification research institution in the UK once carried out an experiment called “air backpack”, which contained a tester for nitrogen dioxide in the air. Two groups of primary school students were asked to take different routes to and from school with “air backpacks” on their backs.

The results showed that most of the students chose the route of walking more to and from school because the “air backpacks” told them that they inhaled less nitrogen dioxide. Industrially developed countries such as the United Kingdom attach great importance to nitrogen dioxide pollution. Most other countries still have difficulty reaching the previous guidance value, and it is even more difficult to catch up with the new AQG.

Removal of nitrogen dioxide in indoor air, reaching the daily average target value of 25µg/m 3 , may become the next outlet in the air purification industry. Infants and young children, family members suffering from cardiopulmonary and metabolic diseases, please pay attention to the new opponent of air pollution, nitrogen dioxide.

Last week, the US Consumer Product Safety Commission announced a plan to ban the sale of new gas stoves which cannot be ‘made safe’ due to fears over indoor nitrogen dioxide pollution

Top image: Tim Foster


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Dennis Heidner
Dennis Heidner
1 year ago

Last week, the US Consumer Product Safety Commission announced a plan to ban the sale of new gas stoves which cannot be ‘made safe’ due to fears over”

The story incorrectly states (paragraph above) that the CPSC announced a plan. THEY DID NOT!

One of the commissioners proposed that since kitchen hoods aren’t being used as they should, noisy, broken or not turned on – that the alternative may be to ban gas stoves to solve the problem.

The reporter should look into the laws and processes that setup up the CPSC. They’d need to do some research, demonstrate that the gas stoves have acceptable alternatives that can be easily used, demonstrate that the gas stove NOx problems can’t be fixed. Release the documents, accept public disclosure and publish the proposal for public comment.

But as it turns out there are possible solutions that have already been released by kitchen hood manufacturers. There also has been previous work that looked at reducing NOx from the stove tops.

Now back to the NOx levels – the measured kitchen values did not appear to be 1 hour averages – instantaneous measurements – yet it looks like they are being compared against the running averages to claim the stoves were much higher than even the outdoor air.

John Wilton-Davies
John Wilton-Davies
1 year ago

The ‘Years of Life Lost” map is completely wrong. The UK, for example, shows “478-634 years of life lost per 100,000 population for PM2.5”. So this means PM kills each of us about 1.5 days early. Rather an understatement. The same applies to all the other data on the map.
Understanding statistics and graphs is rather crucial in this business!

1 year ago

Thank you – but can you direct us to a better map then, please?

1 year ago

Very good to learn about NO2, thank you! Please can you do the same for the other pollutants, such as ozone & VOCs,benzene, butadiene, carbon monoxide, PM, SO2, etc. Which are the msot unhealthy and where do they come from?

1 year ago

Old fashion ozone generators also produce NOx. That’s the main reason ozone generators should not be used in a room while occupied. Medical ozone was developed without the input of air which naturally contains nitrogen. Pure oxygen tanks are used as an intake but it’s very expensive. Now there is a way to use an advanced ozone generator which doesn’t produce NOx like the others.

1 year ago
Reply to  John

Isn’t it also the case that some of the commerical “air purifying” machines use ionisers that produce ozone, or have I go that wrong? And the ozone is bad for anyone with asthma?

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