Nitrogen Dioxide (NO₂)

Description:

The reddish-brown gas is strongly oxidizing and readily soluble in water. Since it is also considered highly toxic and extremely corrosive, the utmost caution is required when handling NO₂.

Nitrogen dioxide is used primarily for producing nitric acid. Through the combination of two NO₂ molecules (dimerization), it also serves as an oxidizer in rocket technology and for producing ammonium nitrate. Nitrogen dioxide is also used as a non-aqueous solvent and in the production of addition compounds with metals. Nitrogen dioxide is heavier than air and collects near the ground.

Limit Values for Nitrogen Dioxide - NO₂:

Different limit values currently apply to outdoor air and indoor spaces. For a one-hour period, the European Union has set a maximum value of 200 µg/m³, 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 multiple locations representative of the respective region, appropriate reduction measures must be taken immediately. This limit value and the recommended measures are still under discussion at the WHO, since simultaneous exposure to other pollutants does not allow for an unambiguous causal relationship.

The Indoor Air Guide Values Committee (AIR) established by the Federal Environment Agency now recommends setting the weekly average value at 40 µg/m³ for indoor spaces as well. However, the one-hour guide value of 80 µg/m³ and the short-term hazard value of 250 µg/m³ still apply here. If this is exceeded, action must be taken immediately.

A workplace exposure limit of 950 µg/m³ has been set for NO₂. This must be observed over a period of eight hours. It may be briefly exceeded by up to twice this value up to four times per shift. This value applies in particular to workers who are exposed to elevated nitrogen dioxide levels at their workplace.

Effects of Excessive Concentration:

Inhaling NO₂ narrows the bronchi. This is why patients with bronchial asthma or chronic bronchitis react particularly sensitively to high nitrogen dioxide exposure.

Highly toxic nitrogen dioxide can only be perceived by its characteristic pungent odor at higher concentrations. However, even a small proportion of NO₂ in the air we breathe can cause dizziness and headaches. Higher nitrogen dioxide concentrations can lead to shortness of breath and fluid accumulation in the lungs (pulmonary edema). These carry the risk of resulting chronic lung damage, irritation of the respiratory tract, or chest pain, and in the worst case, death.

Further long-term health effects of high nitrogen dioxide exposure are still being investigated. These include cardiovascular disease, diabetes mellitus, and immune system disorders. There is also evidence of reduced fertility.

Formation of NO₂:

The combustion of fossil fuels (mainly coal, gas, and oil) also produces nitrogen dioxide. NO₂ is thus emitted through exhaust from motor vehicles and aircraft, coal- and gas-fired power plants, and various heating boilers. Indoors, nitrogen dioxide is released by open fireplaces (stoves, fireplaces, candles, etc.) and tobacco smoke.

Nitrogen dioxide is also produced during paper manufacturing. In addition, there are natural NO₂ sources. These include, besides the nitrogen dioxide present in the atmosphere, microbiological conversion processes in the soil.

Sensor Used:

Nitrogen dioxide is measured using an electrochemical sensor. NO₂ molecules that "dock" onto the sensor's surface cause a small current in the sensor. The advantage of our sensor is the manufacturer's individual sensitivity calibration, its particularly long service life, and greatly reduced cross-sensitivities.

The sensor we use has a slight cross-sensitivity to ozone (O₃). It also reacts somewhat to this gas, showing a slight deflection even when no NO₂ is present.

Measuring Nitrogen Dioxide:

As a particularly powerful and comprehensive air analyzer, the air-⁠Q also features a sensor that can measure nitrogen dioxide in indoor air. Many facts about the air-⁠Q's technology can be found here. You can order the air-⁠Q in the online shop.