Nitrogen Dioxide


Other names: nitrogen oxide, nitro, nitrito, NO 2
Chemical Formula: NO 2
Mass fractions: N (nitrogen) 30.4%, O (oxygen) 69.6%
CAS Number: 10102-44-0
Molecular weight: 46.0055 g/mol
Solubility:  reacts in water
Melting point: -11o C
Boiling point: 21o C









Structure diagram:


What is Nitrogen Dioxide?


Nitrogen Dioxide is emitted from high temperature combustion. This can be seen as the brown haze downwind of cities. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants. It is present in vehicle exhaust and the fumes from burning fuel oil, kerosene, propane, natural gas or wood. When NO2 is exposed to water, it can form nitric acid, which is a chemical that contributes to acid rain. Nitrogen dioxide is also a major cause of smog. 

How can one be exposed to nitrogen dioxide?

People are exposed to NO2 by breathing in the gas from polluted air. The levels of O2 are usually higher outdoors than indoors. The operation of gas or diesel engines can result in a build up of dangerous levels of NO2 in the air. Most of the nitrogen dioxide in cities comes from motor vehicle exhausts (about 80%).

What are the effects of exposure to nitrogen dioxide?

Individual exposure to NO2 depends mainly on local outdoor concentrations. However, it can also be affected by indoor pollution sources such as tobacco smoking and unvented cooking or heating appliances using gas. Populations living near busy roads are particularly exposed to and affected by NO2 pollution. Studies have shown that short term peak exposures can increase respiratory allergic reactions.

Measurements of nitrogen dioxide?

Because high concentrations of nitrogen dioxide can have adverse effects on human health, Governments around the world are taking steps to manage and reduce the amount of nitrogen dioxide produced. These include implementing fuel quality standards, implementing vehicle emission standards, developing alternative fuels and developing pollution forecasting systems. All this depends upon the ability to measure nitrogen dioxide cost effectively. Monitoring air quality in the microenvironment is critical in understanding epidemiological effects, for environmental assessments, for transportation planning, and for making decisions about air pollution mitigation strategies.

Sources of Nitrogen Dioxide

Kerosene heaters, un-vented gas stoves and heaters, environmental tobacco smoke.

Standards or Guidelines

No standards have been agreed upon for nitrogen oxides in indoor air.  ASHRAE and US EPA National Ambient Air Quality Standards list 0.053 ppm as the avearage 24-hour limit for NO2 in outdoor air.

Link to US EPA page on NO2: https://www.epa.gov/air/nitrogenoxides/


Toxicity properties:

Short-term exposure limit 9 mg/m3
Long-term exposure limit 5 mg/m3