Nitrogen Dioxide


Nitrogen dioxide is the chemical compound with the formula NO2. It is one of several nitrogen oxides. [1] Nitrogen dioxide is non-flammable and colourless to brown at room temperature. It has a strong, harsh odour and is a liquid at room temperature, becoming a reddish-brown gas above 70F. [2] NO2 is an intermediate in the industrial synthesis of nitric acid. [1] Some nitrogen dioxide is formed naturally in the atmosphere by lightning and plants, soil and water produce some. However, only about 1% of the total amount of nitrogen dioxide found in our cities’ air is formed this way. Nitrogen dioxide is an important air pollutant because it contributes to the formation of photochemical smog, which can have significant impacts on human health. [3]

Uses [4]

Nitrogen dioxide has been used as a catalyst in certain oxidation reactions; as an inhibitor to prevent polymerisation of acrylates during distillation; as a nitrating agent for organic compounds; as an oxidising agent; as a rocket fuel; as a flour-bleaching agent and in increasing the wet strength of paper.

Sources & Routes of Exposure

Sources of Exposure [3]

The major source of nitrogen dioxide in Australia is the burning of fossil fuels: coal, oil and gas. Most of the nitrogen dioxide in cities comes from motor vehicle exhaust (about 80%). Other sources of nitrogen dioxide are petrol and metal refining, electricity generation from coal-fired power stations, other manufacturing industries and food processing. Unflued gas heaters and cookers are the major sources of nitrogen dioxide in Australian homes.

Routes of Exposure [2]

  • The general population is primarily exposed to nitrogen dioxide by breathing in air. People who live near combustion sources such as coal burning power plants or areas with heavy motor vehicle use may be exposed to higher levels of nitrogen dioxide.
  • Households that burn a lot of wood or use kerosene heaters and gas stoves tend to have higher levels of nitrogen dioxides in them when compared to houses without these appliances.
  • Nitrogen dioxide is found in tobacco smoke, so people who smoke or breathe in second-hand smoke may be exposed to it.
  • Workers employed in facilities that produce nitric acid or certain explosives like dynamite and trinitrotoluene (TNT), as well as workers involved in the welding of metals may breathe in nitrogen dioxide during their work.

Health Effects [5]

Acute Effects

  • Contact can irritate and burn skin and eyes with possible eye damage.
  • Breathing nitrogen dioxide can irritate the throat and nose.
  • Breathing nitrogen dioxide can irritate the lungs causing coughing and/or a shortness of breath. Higher exposures can cause a build-up of fluid in the lungs (pulmonary oedema), a medical emergency, with severe shortness of breath.
  • High levels can interfere with the ability of the blood to carry oxygen causing headache, fatigue, dizziness, and a blue colour to the skin and lips (methemoglobinemia).
  • Higher levels can cause trouble breathing, collapse and even death.

Chronic Hazard

  • Repeated exposure to high levels may lead to permanent lung damage.

Cancer Hazard

    • Nitrogen dioxide may cause mutations (genetic changes).
    • There is no evidence that nitrogen dioxide causes cancer in animals.

Reporductive Hazard

  • There is limited evidence that nitrogen dioxide may damage the developing foetus; and
  • Decrease fertility in females.

Safety [6]

First Aid Measures

  • If inhaled: If breathed in, move person into fresh air. If not breathing, give artificial respiration. Consult a physician.
  • In case of skin contact: Take off contaminated clothing and shoes immediately. Wash off with soap and plenty of water. Take victim immediately to hospital. Consult a physician.
  • In case of eye contact: Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
  • If swallowed: Do NOT induce vomiting. Never give anything by mouth to an unconscious person. Rinse mouth with water. Consult a physician.

Exposure Controls & Personal Protection

Engineering Controls

  • Avoid contact with skin, eyes and clothing.
  • Wash hands before breaks and immediately after handling the product.

Personal Protective Equipment

The following personal protective equipment is recommended when handling nitrogen dioxide:

Eye/face protection

  • Tightly fitting safety goggles.
  • Faceshield (8-inch minimum).
  • Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).

Skin protection

  • Handle with gloves.
  • Gloves must be inspected prior to use.
  • Use proper glove removal technique (without touching gloves’ outer surface) to avoid skin contact with this product.
  • Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices.
  • Wash and dry hands.
  • The selected protective gloves have to satisfy the specifications of EU Directive 89/686/EEC and the standard EN 374 derived from it.

Body Protection

  • Complete suit protecting against chemicals.
  • The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.

Respiratory Protection

  • Where risk assessment shows air-purifying respirators are appropriate use a full-face respirator with multi-purpose combination (US) or type AXBEK (EN 14387) respirator cartridges as a backup to engineering controls.
  • If the respirator is the sole means of protection, use a full-face supplied air respirator.
  • Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).


United States [7]

Exposure Limit
Limit Values
HE Codes
Health Factors and Target Organs

OSHA Permissible Exposure Limit (PEL) General Industry

(9 mg/m3) Ceiling


Chronic bronchitis, emphysema


Eye, nose, and upper respiratory irritation

OSHA PEL Construction Industry

(9 mg/m3) Ceiling


Chronic bronchitis, emphysema


Eye, nose, and upper respiratory irritation

OSHA PEL Shipyard Employment

(9 mg/m3) Ceiling


Chronic bronchitis, emphysema


Eye, nose, and upper respiratory irritation

National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL)

(1.8 mg/m3) STEL


Mild headache


Bronchiolitis obliterans


Acute pulmonary oedema; lower respiratory irritation (cough, dyspnea)


Eyes, nose, and throat irritation

American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) (2012)

(0.38 mg/m3)



Lower respiratory irritation


(1.8 mg/m3) STEL



Australia [8]

Safe Work Australia

Chemical name


TWA (ppm)







Advisory carcinogen category

Nitrogen dioxide






Carc. 2