Nitrogen dioxide is a chemical compound with the formula NO2.
It is one of several nitrogen oxides.
NO2 is an intermediate in the industrial synthesis of nitric acid, used primarily in the production of fertilizers.
At higher temperatures it is a reddish-brown gas that can be fatal if inhaled in large quantity.
Nitrogen dioxide is a reddish-brown gas above 21.2 °C with a pungent, acrid odor.
Nitrogen dioxide becomes a yellowish-brown liquid below 21.2 °C and converts to the colorless dinitrogen tetroxide below −11.2 °C.
The reddish-brown color is a consequence of preferential absorption of light in the blue region of the spectrum (400 – 500 nm).
although the absorption extends throughout the visible (at shorter wavelengths) and into the infrared (at longer wavelengths). Absorption of light at wavelengths shorter than about 400 nm results in photolysis (to form NO + O, atomic oxygen); in the atmosphere the addition of O atom so formed to O2 results in ozone formation.
Nitrogen dioxide appears via the oxidation of nitric oxide by oxygen in air:
2 NO + O2 → 2 NO2
Nitrogen dioxide is formed in most combustion processes using air as the oxidant.
At elevated temperatures nitrogen combines with oxygen to form nitric oxide.
NO2 is introduced into the environment by natural causes: stratosphere, bacterial respiration, volcanos, and lightning.
NO2 is a trace gas in the atmosphere absorbing sunlight and regulating the chemistry of the troposphere, especially in determining ozone concentrations.
NO2 is used in the manufacturing of nitric acid, as a nitrating agent in chemical explosives, as a polymerization inhibitor for acrylates, as a flour bleaching agent, and as a room temperature sterilization, and as an oxidizer in rocket fuel.
The most prominent sources of NO2 are internal combustion engines burning fossil fuels.
Outdoors, NO2 can be a result of traffic from motor vehicles.
Indoors, exposure arises from cigarette smoke, and butane and kerosene heaters and stoves.
Industrial workers exposed to NO2 is are at risk for occupational lung disease.
Agricultural workers exposed to NO2 arising from grain decomposing in silos;
lung damage in a condition called “Silo-filler’s disease”.
Nitrogen dioxide is also produced by atmospheric nuclear tests, and is responsible for the reddish color of mushroom clouds.
Gaseous NO2 diffuses into the epithelial lining fluid of the respiratory epithelium and dissolves, chemically reacting with its antioxidant and lipid molecules.
The health effects of NO2 are caused by the reaction products or their metabolites.
NO2 metabolites are reactive nitrogen species and reactive oxygen species that can drive bronchoconstriction, inflammation, reduced immune response, and may have effects on the heart.
Acute harm due to NO2 exposure is only likely to arise in occupational settings.
NO2 exposure to the skin can cause irritations and burns.
At high concentrations of the gaseous form cause immediate distress: 100–200 ppm can cause mild irritation of the nose and throat : 250–500 ppm can cause edema, leading to bronchitis or pneumonia, and levels above 1000 ppm can cause death due to asphyxiation from fluid in the lungs.
Initial symptoms at the time of exposure include transient cough, fatigue or nausea, and over hours inflammation in the lungs causes edema.
Management:
For skin or eye exposure, flushing with saline.
For inhalation, oxygen, bronchodilators may be administered, and if there are signs of ((methemoglobinemia)), methylene blue may be administered.
It is classified as an extremely hazardous substance in the United States, and it is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
Chronic exposure to NO2 can cause respiratory effects including airway inflammation and increased respiratory symptoms in people with asthma.
NO2 creates ozone which causes eye irritation and exacerbates respiratory conditions, leading to increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma.
Home insulation is improving, and this can result in greater retention of indoor air pollutants, such as NO2.
Indoor home exposure to NO2 occurs with the use of gas stoves for cooking or heating.
Indoor exposure levels of NO2 are, on average, at least three times higher in homes with gas stoves compared to electric stoves.
While using a gas stove, it is advised to also use ventilation.
The highest levels of NO2 are in multifamily homes.
Exposure to NO2 is especially harmful for children with asthma: children with asthma who live in homes with gas stoves have greater risk of respiratory symptoms such as wheezing, cough and chest tightness.
Gas stoves use is associated with reduced lung function in girls with asthma.
NO2 toxicity is dangerous for children.
The interaction of NO2 and other NOxides with water, oxygen and other chemicals in the atmosphere can form acid rain which harms sensitive ecosystems such as lakes and forests.
Elevated levels of NO2 can also harm vegetation, decreasing growth, and reduce crop yields.
Replacing gas stoves with electric ranges could greatly reduce the exposure to indoor NO2 and improve the respiratory function of children with asthma.
You can also prevent NO2 exposure by avoiding cigarette smoking and not idling your car whenever possible.
EPA has set safety levels for environmental exposure to NO2 at 100 ppb, averaged over one hour, and 53 ppb, averaged annually.
In-vehicle concentrations can be 2–3 times higher than measured at nearby area-wide monitors.
Near-roadway concentrations of NO2 have been measured to be approximately 30 to 100% higher than concentrations away from roadways.
Individuals who spend time on or near major roadways can experience short-term NO2 exposures.
There is a connection between breathing elevated short-term NO2 concentrations, and increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma.
NO2 roadway exposure concentrations endanger susceptible individuals, including asthmatics, children, and the elderly.