Difference between outdoor air and workplace limit value for NO2, Federal Environment Agency

The values for office workplaces and private rooms are significantly lower.

Source: kerkezz / Fotolia.com”>click to enlargeThe workplace limit value for NO2 applies to workers at some industrial workplaces.

The values for office workplaces and private rooms are significantly lower.

The EU limit value (annual average) for the concentration of nitrogen dioxide (NO2) in the outside air is 40 µg/m³ – the occupational exposure limit value of 950 µg/m³ is considerably higher. An occupational exposure limit value is a value for the temporary exposure of healthy workers, while NO2 in the outside air can also affect sensitive people around the clock.

When deriving limit values for nitrogen dioxide in the outside air, the same standards cannot be applied as for workplace limit values (deriving from the maximum workplace concentration, MAK). The MAK value for NO2 is a scientific recommendation of the Standing Senate Commission for the Testing of Health Hazardous Substances of the German Research Foundation (DFG) and also corresponds to the workplace limit value (AGW) of the Ordinance on Hazardous Substances (GefStoffV). Occupational exposure limit values only apply to workers at industrial workplaces and in trades where an increased nitrogen dioxide load is to be expected due to the use or production of certain substances. Nitrogen dioxide, for example, is produced – or used – in welding processes, in the production of dynamite and nitrocellulose or in the use of diesel engines. Among other things, the workplace limit value has a different time and personal reference than the outdoor limit value: the value applies to healthy workers eight hours a day and for a maximum of 40 hours a week. Workers who are exposed to occupational pollutants also receive occupational health care and are therefore more closely monitored than the general population.

Nitrogen dioxide in the outside air, on the other hand, is exposed to everyone around the clock, although the concentration can vary depending on where they are. Sensitive people such as children, pregnant women, the elderly or people with pre-existing conditions such as asthma are in some cases much more sensitive to environmental influences. Limit values for pollutants in the outside air are based on their long-term health effects on the population groups studied, which have been observed in studies over decades.

MAK values do not apply to office workplaces or private rooms. The guideline values of the Committee for Indoor Air Quality Standards (AIR), formerly the ad hoc working group of the Indoor Air Hygiene Commission (IRK) and the Working Group of the Supreme State Health Authorities (AOLG), apply. At the end of 2018, the Committee revised and updated the previously applicable guideline values. The short-term guide value II is 250 µg NO2/m3 (hazard value) and the short-term guide value I (precautionary value) is 80 µg NO2/m 3. The measurement period is one hour. If a long-term assessment is required, AIR recommends the use of the WHO’s indoor air conductance of 40 µg NO2/m³ as the assessment standard for the assessment of long-term exposure. The short-term guide value II is an effect-related value which must be acted upon immediately if it is reached or exceeded. This higher concentration can be a health hazard, especially for sensitive persons staying permanently in the rooms.

Very high concentrations of nitrogen dioxide can be produced indoors, particularly as a result of combustion processes such as the use of fireplaces, gas stoves or wood-burning stoves. However, in the absence of such sources indoors, the quality of indoor air is directly affected by outdoor air pollution: high concentrations of nitrogen dioxide in the outdoor air, for example near busy roads, can also lead to a higher level of pollution indoors.

The derivation of occupational exposure limit values is usually based on studies of test persons or animal experiments. As a rule, the subject studies are designed in such a way that healthy middle-aged persons (so-called “healthy workers”) participate in these studies. In addition, the persons are often not examined in an everyday environment but, for example, at the respective workplaces, so that a possible interaction with other pollutants of everyday life is excluded. The underlying studies are not always long-term and cannot therefore reflect the consequences of decades of comparatively low nitrogen dioxide concentrations from everyday life outside the workplace. The total lifetime of a human being contains considerably longer exposure times than a pure working life. This must also be taken into account here.

The EU limit value for the annual average concentration of nitrogen dioxide in ambient air is in line with World Health Organisation (WHO) recommendations. The limit value is derived from population-based studies, which also include sensitive groups of people and sensitive periods of life. Thus, for the assessment of the health protection of the general population against nitrogen dioxide in the outside air, the EU limit value or the WHO guideline value of 40 µg/m³ on an annual average is to be used.

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Christina Cherry
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