Nitrogen dioxide (NO₂) belongs to the group of nitrogen oxides. It is a reddish-brown, chlorine-like and pungent smelling gas.NO₂ has a strong irritating effect on the respiratory tract and promotes asthma.
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The reddish-brown gas is strongly oxidising and highly soluble in water. As it is also considered highly toxic and extremely corrosive, extreme caution is required when handling NO₂.
Nitrogen dioxide is mainly used in the production of nitric acid. By combining two NO₂ molecules (dimerisation), it also serves as an oxidising agent in rocket technology and for the production of ammonium nitrate. Furthermore, nitrogen dioxide is used as a non-aqueous solvent and in the production of addition compounds with metals. Nitrogen dioxide is heavier than air and accumulates on the ground.
Until now, different limit values have applied to outdoor air and indoor spaces. For the period of one hour, the European Union has designated a value of 200 µg/m³ as the maximum limit, which may not be exceeded more than 18 times per year. If the binding annual limit value of 400 μg/m³ is exceeded within three hours at several locations that are representative for the respective region, suitable measures for reduction must be taken immediately. This limit value as well as the recommended measures are still under discussion for the WHO, since simultaneous exposure to other pollutants does not allow for a one-to-one causal relationship.
The Committee for Indoor Reference Values (AIR) set up by the Federal Environment Agency now recommends setting the weekly mean value at 40 µg/m³ indoors as well. However, the one-hour guideline value of 80 µg/m³ and the short-term danger value of 250 µg/m³ still apply here. If this is exceeded, immediate action must be taken.
The occupational exposure limit value for NO₂ was set at 950 µg/m³. This must be complied with over a period of eight hours. It may be exceeded up to four times per shift for a short period of time. This value applies in particular to those workers who are exposed to increased nitrogen dioxide pollution at their workplace.
Breathing in NO₂ causes the bronchial tubes to constrict. Therefore, patients with bronchial asthma or chronic bronchitis are particularly sensitive to high nitrogen dioxide exposure.
The highly toxic nitrogen dioxide can only be perceived in larger concentrations by its characteristic pungent odour. However, even at lower levels of NO₂ in the air we breathe, dizziness and headaches can occur. Higher nitrogen dioxide concentrations can lead to shortness of breath and water accumulation in the lungs (pulmonary oedema). These carry the risk of resulting in chronic lung damage, irritation of the respiratory tract or chest pain, and in the worst case lead to death.
Other late health effects of excessive nitrogen dioxide pollution are still under review. These include cardiovascular diseases, diabetes mellitus and immune system disorders. There are also indications of reduced fertility.
The combustion of fossil fuels (especially coal, gas and oil) also produces nitrogen dioxide. This means that NO₂ is emitted by exhaust gases from motor and aviation vehicles, coal and gas-fired power plants and various boilers. Indoors, nitrogen dioxide is released by open fires (stoves, fireplaces, candles, etc.) and tobacco smoke.
Furthermore, nitrogen dioxide is produced during paper production. There are also natural NO₂ sources. In addition to nitrogen dioxide in the atmosphere, these also include microbiological conversion processes in the soil.
Nitrogen dioxide is measured by means of an electrochemical sensor. NO₂ molecules that "dock" on the surface of the sensor cause a small current in the sensor. The advantage of our sensor is the individual sensitivity calibration by the manufacturer and the particularly long service life as well as greatly reduced cross-sensitivities.
The sensor we use has a slight cross-sensitivity to ozone (O₃). It therefore also reacts somewhat to this gas and then shows a slight deflection even if no NO₂ is present.
As a particularly powerful and comprehensive air analyser, the air-Q also has a sensor that can measure nitrogen dioxide in the room air. Many facts about the technology of the air-Q can be found here. You can order the air-Q in the online shop.
