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Air pollutants: Nitrogen Dioxide

What’s nitrogen dioxide?

burning of fossil fuels

Nitrogen Dioxide is a chemical compound with the formula NO2, but it is usually defined as an indicator for a highly reactive gases group known as oxides of nitrogen or nitrogen oxides (NOx).

Its smell and color are the only properties of nitrogen dioxide perceptible for humans without any special equipment. NO2 has a biting and pungent odor and it is easily recognizable with a red-brown color at gas stage (over 21.2 °C) and yellow-brown looking at liquid’s (between 21.2 and -11.2 °C).

Nitrogen dioxide uses

Nitrogen dioxide is released in wide variety of situations and processes that involve nitrogen. Here are some examples:

  • Nitric acid manufacturing.
  • Nitrating agent in chemical explosives manufacturing.
  • Room temperature sterilization agent.
  • Oxidizing rockets fuel.
  • Polymerization inhibitor for acrylates.

Sources of nitrogen dioxide pollution

Nitrogen dioxide emissions to the atmosphere are processes that contribute to worsen the air quality, and this is the reason why it is considered criteria pollutant. Nitrogen oxides are produced by human activity 99% of the time, and produced naturally the other 1% during thunderstorms by electric discharge.

Outdoors, cars and combustion engines burning fossil fuels are the number one responsible for nitrogen dioxide emissions. Indoors, NO2 emissions are mainly produced by sources like cigarettes, butane, kerosene heaters and stoves.

traffic jam

Indirectly, nitrogen monoxide emissions also contribute to the formation of nitrogen dioxide since the first reacts with oxygen or ozone to produce the second.

Nitrogen dioxide health and environmental effects

As indicator of the NOx group, nitrogen dioxide is responsible for several health and environmental effects. NO2 reacts with other gases to create adverse meteorological conditions, such as acid rain or ground-level ozone, known for being a threat to humans and wildlife.

Health effects on humans

Nitrogen dioxide, as well as its NOx siblings, lead to respiratory problems when inhaled since they can penetrate deeply into sensitive lung tissue. Some symptoms are coughing, wheezing or difficulties to breathe.

However, these nitrogen oxides need to react with other compounds like ammonia, volatile organic compounds (VOCs) or common organic chemicals to become extremely harmful, causing then similar health effects than NO2.

Long-term exposure could carry the development of asthma, emphysema, bronchitis or other respiratory diseases and infections. It can also aggravate cardiovascular problems such as heart diseases. Moreover, in extreme conditions, breathing polluted air with high levels of nitrogen dioxide may even cause premature death.

Sensitive groups such as children, elderly or people with respiratory problems are more affected by the exposure to this pollutant. For these groups, it is recommended controlling NOx levels and emissions, especially for NO2 and NO, with devices such as nitrogen dioxide detectors (that can even be portables).

How does nitrogen dioxide pollution affect our planet?

Nitrogen dioxide’s main partner in the NOx group is nitric oxide or nitrogen monoxide (NO). As already said, both help in the development of environmental effects like smog, acid rain or tropospheric ozone.

Nitrogen dioxide or any others NOx react with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain damages vegetation, buildings, water bodies and all the living beings on these environments.

Despite nitrogen is essential for plants nutrition, high levels of nitrogen dioxide or nitrogen monoxide may damage their lives. Nitrogen oxides in the atmosphere contribute to nutrient pollution in coastal waters and nitrate particles affect the visibility and create hazy air.

How is NO2 pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Nitrogen dioxide is considered both a primary and secondary criteria pollutant, as it can be extremely dangerous for the environment and the public safety. As mentioned, it acts as the indicator for the nitrogen oxides group, and the maximum permitted or recommended levels for NO2 are:

  • World Health Organization (WHO) guidelines: 200 μg/m³ and 40 μg/m³ for an average periods of 1 hour and 1 year, respectively.
  • NAAQS: 0,1 ppm of 1-hour daily maximum concentrations, averaged over 3 years, while annual mean cannot exceed 0,053 ppm (100 μg/m³).

EU Air Quality Directive: exactly the same as WHO guidelines, 200 μg/m³ for 1 hour (cannot be exceeded more than 18 times per year) and 40 μg/m³ annually.

2 thoughts on “Air pollutants: Nitrogen Dioxide

  1. Thanks for explaining that high levels of nitrogen dioxide can damage the lives of plants. I’ve been trying to learn more about how fumes and dust are controlled, especially in industrial settings. I’m glad I read your article because it helped me understand the importance of pollution control.

    1. We are glad to know our article helped you. If you have any other questions related to nitrogen dioxide or other kind of air pollution don’t hestitate to ask it.

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