Molecular formula: NOx/NO2
Characteristics: The two most common oxides of nitrogen are nitric oxide (NO) and nitrogen dioxide (NO2). This gas has a reddish-brown colour and a pungent smell.
Occurrence: Oxides of nitrogen form a natural part of the environment. They generally occur in industry as a result of fossil fuel combustion at high temperatures. Oxides of nitrogen can be deposited to households from the air, smoking, or a gas heater. They also get into the air from vehicle exhausts. NO is one of the substances that contribute to the greenhouse effect.
Impact: The primary toxic effect of nitrogen dioxide is irritation of the mucous membranes. The first signs of intoxication manifest themselves by smarting eyes, a drop in blood pressure, headaches, and respiratory problems. Chronic poisoning may cause a heightened frequency of tooth decay or conjunctivitis. Nitrogen dioxide easily gets into the lungs and bloodstream, and since it is poorly soluble in water, it penetrates inside the lower airways. Children, sensitive individuals, and asthmatics are more vulnerable to this risk.
Limit: The safe limit for short-term concentrations – 30 minutes – according to the EU and WHO is 200 µg/m3 (micrograms per cubic metre).