Questions on Nitrogen Dioxide

1. What is Nitrogen Dioxide (NO₂)?
2. How does NO₂ affect human health?
3. How are we exposed to NO₂?
4. Should current NO₂ guidelines be reconsidered?
5. Conclusions on NO₂

See also:
General issues & Recommendations

1. What is Nitrogen Dioxide (NO₂)?

Nitrogen dioxide is part of a group of gaseous air pollutants produced as a result of road traffic and other fossil fuel combustion processes.

Its presence in air contributes to the formation and modification of other air pollutants, such as ozone and particulate matter, and to acid rain. More...

2. How does Nitrogen Dioxide (NO₂) affect human health?

2.1 Studies on human populations indicate that long-term exposure to NO₂ levels currently observed in Europe may decrease lung function and increase the risk of respiratory symptoms such as acute bronchitis and cough and phlegm, particularly in children. Even though some studies have shown associations between NO2 exposure and mortality, present evidence is not sufficient to conclude that effects on mortality can be attributed to long-term exposure to NO2 itself (see also 3.3). More...

2.2 NO₂ alone has been shown to cause acute health effects in controlled human exposure studies. Studies on human populations have not been able to isolate potential effects of NO₂, because of the complex link between concentrations in ambient air of NO₂, particulate matter, and ozone. More...

2.3 Several studies have shown that NO₂ exposure increases allergic responses to inhaled pollens. More...

2.4 People with asthma and children in general are considered to be more vulnerable to NO₂ exposure. More...

2.5 There is no evidence for a threshold for exposure to NO₂ below which no effects on health are expected. More...

3. How are we exposed to Nitrogen Dioxide (NO₂)?

3.1 In Europe, NO₂ air pollution is mainly caused by motor vehicles and, in some places, by energy production. More...

3.2 Individual exposure to NO₂ depends mainly on local outdoor concentrations. However, it can also be affected by indoor pollution sources such as tobacco smoking and unvented cooking or heating appliances using gas. More...

3.3 Populations living near busy roads are particularly exposed to and affected by NO₂ pollution . Studies have shown that short term peak exposures can increase respiratory allergic reactions. Even though some studies have shown associations between NO2 exposure and mortality, present evidence is not sufficient to conclude that effects on mortality can be attributed to long-term exposure to NO2 itself (see also 2.1). More...

The map below illustrates regions where traffic and fuel combustion contribute to NO₂ air pollution. It shows the mean ground level nitrogen dioxide (NO₂) concentration between January 2003 and June 2004, as measured by Satelite.

Source: European Space Agency www.esa.int/esaCP/ Credits: University of Heidelberg

4. Should current NO₂ guidelines be reconsidered?

4.1 No significant reductions in ambient NO₂ concentrations have been witnessed. Hence, it is not known how such reductions could affect public health. More...

4.2 When setting guidelines to protect human health, both short-term (one hour or one day) and long term (one year) average NO₂ concentrations are relevant. More...

4.3 Current WHO guideline values for NO₂ already address both short-term exposure to emission peaks and long-term exposure throughout the year. However, because adverse effects have been observed within a range that includes the current annual WHO guideline value, it is recommended to maintain or lower that value. More...