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NO2 Gas and its Sensor

Intro to Nitrogen Dioxide

Nitrogen dioxide (NO2) is one component of the highly reactive gases known as the oxides of nitrogen or nitrogen oxides (NOx). NO2 is created from the reaction of nitrogen and oxygen during the combustion process. Fuel and thermal are the most common formation types.

A higher risk area for industrial workers from NO2 is in poorly ventilated areas such as a confined spaces which can result in asphyxiation or toxic exposure. Emissions from power plants has also been found to cause lung function abnormalities in subsequent workers. Other common sources are from the emissions of cars, trucks, buses, and off-road equipment. Large cities with many motor vehicles, high temperatures, and lightning can heighten the levels in the air. NO2 and NOx is widely known for causing air pollution in the form of smog, acid rain, and tropospheric ozone.

Gas Characteristics

  • Yellowish-brown liquid or reddish-brown gas (above 70F)
  • Pungent, acrid odor
  • Heavier than air
  • Fatal if inhaled
  • May cause or intensify fire—oxidizer
  • Reacts with water to form nitric acid.
  • Contains gas under pressure, may explode if heated.
  • OTHER NAMES: NO2, nitrogen oxide, nitrogen dioxide, nitrogen peroxide, dinitrogen tetroxide, nitrito
  • CAS 10102-44-0

Industrial NO2 hazards and sources

  • Vehicle emissions is the largest source of atmospheric NO2
  • Industrial sources are the second largest cause
  • Power plants
  • Thermal power stations
  • Wastewater treatment plants
  • Petroleum production and refining
  • Pulp and paper processing
  • Diesel-powered equipment
  • Agriculture: Fermentation in domed cylindrical silos 
  • NO2 is produced industrially as an inhibitor to prevent polymerization of acrylates during distillation
  • Nitrating agent for organic compounds, oxidizing agent, rocket fuel, a flour bleaching agent
  • Indoor risks from kerosene or gas space heaters and gas stoves

NO2 is heavier than air, exposure in a poorly ventilated area, like a confined space can result in asphyxiation.


High Risk Scenarios

  • Nitrogen dioxide is heavier than air, exposure in a poorly ventilated area such as a confined space can result in asphyxiation.
  • Breathing air contaminated with NO2 can cause respiratory issues—coughing, wheezing, or difficult breathing. Longer exposures can cause asthma or respiratory infections.
  • Industrial power plant workers exposed to NO2 emissions are likely to experience lung function abnormalities.
  • Can cause severe skin burns and eye damage.

NO2 Sensor Info

Type: Electrochemical 
Range: 0-50 ppm (0.1 ppm resolution)

Default Alarm Levels

Low Alarm: 2.5 ppm
High Alarm: 5  ppm
STEL — 15 minute — Short Term Exposure Limit: 5 ppm 
TWA  — 8 hour time weighted average: 2.5 ppm 

Blackline devices that can detect NO2

Questions about the detection of NO2?


Special Applications and Considerations

  • Store locked up, in an upright secure container. Protect from sunlight. Store in a well-ventilated place.
  • Ensure adequate ventilation when using in an industrial setting. Use process enclosures, local exhaust ventilation, or other engineering controls to keep worker exposure at safe limits.
  • Avoid eating, drinking, or smoking in areas where NO2 is handled, stored, or processed. Thoroughly wash hands and face before engaging in break activities.


  • Highly reactive with: combustible materials, reducing materials, grease, and oil.
  • Nitrogen dioxide reacts with water, oxygen, and other chemicals in the atmosphere to from acid rain. Acid rain can cause harmful affects to lakes and forests.
  • Nitrogen oxides are irritating to the eyes, skin, mucous membranes, and respiratory tract.

Health Risks and Handling of NO2

0.2 ppm
Normal levels with no health impacts for a short period of time. 8 hours at this level minor symptoms can begin.
1 ppm
Mild headache, acute pulmonary edema, lower respiratory irritation (cough, dyspnea), eyes, nose, and upper respiratory irritation.
5 ppm
Chronic bronchitis, emphysema, irritation of the eyes, nose, and upper respiratory.
15 ppm
Coughing wheezing, difficulty breathing, and flu-like symptoms,. Can be exposed for 1 hour before experiencing irreversible symptoms.
20 ppm
Immediately dangerous to life or health.
  • Inhalation: Remove person to fresh air and keep comfortable for breathing. Call poison center or physician right away. Nitrogen oxides are irritating to the upper respiratory tract and lungs even at low concentrations. Even one or two breaths of a high concentration can cause toxicity.
  • Ingestion: Immediately call a poison center or physician. Rinse mouth. Don't induce vomiting. Nitrogen dioxide exists as a liquid below 21 degrees Celsius and can cause gastrointestinal irritation.
  • Skin contact: take off contaminated clothing. Rinse skin with water. Call poison control or a physician right away. Can cause severe burns and may cause frostbite.
  • Eye contact: Rinse cautiously with water for several minutes. Remove contact lenses if applicable. Continue rinsing. Call a poison center or physician. Can cause serious eye damage. Contact with rapidly expanding gas can cause burns and frostbite.

  • Take action only if you've been trained. Evacuate the surrounding area. Turn off all possible sources of ignition. Don't inhale gas and ensure the area is well ventilated. Wear a respirator if ventilation isn't adequate. Workers should be wearing personal protective equipment.
  • In case of a spill: Immediately contact emergency personnel. Stop leak if there isn't a risk to yourself. Use spark-proof tools and explosion-proof equipment.


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