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

3.1 Critical sources of NO₂ responsible for health effects?
3.2 Relationship between ambient levels and personal exposure to NO₂
3.3 Short-term exposure to high peak levels or exposure in hot spots for NO₂

3.1 Which are the critical sources of NO₂ responsible for health effects?

WHO states: "In most urban environments in Europe, the principal source of NO₂ is NO_x from motor vehicles of all types and energy production in some places [e.g., power plants, domestic heating]." More..

Source & © : WHO Europe (2003)

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

3.2 What is the relationship between ambient levels and personal exposure to NO₂?

Can the differences influence the results of studies?

WHO states: "In any particular setting the answer will depend on the relative contributions of outdoor and indoor sources and on personal activity patterns. A direct relationship between personal exposure and outdoor concentrations is found in the absence of exposure to indoor sources such as unvented cooking or heating appliances using gas, and tobacco smoking. However, since outdoor NO₂ is subject to wide variations caused by differences in proximity to road traffic and local weather conditions, the relationship of personal exposure to measurements made at outdoor monitoring stations is variable. Results of epidemiological studies relying on outdoor NO₂ concentrations may be difficult to interpret if account is not taken of exposure to indoor sources." More...

Source & © : WHO Europe (2003)

3.3 What is the health relevance and importance of short-term exposure to high peak levels or exposure in hot spots for NO₂?

Adverse health effects have been documented after short-term exposure to peaks, as well as after long-term exposure to relatively low concentrations of NO₂. Experimental studies indicate that short-term exposure to high concentrations of NO₂ increases responsiveness to allergens. NO₂ exposure over time has also been linked to mortality and disease progression. A direct comparison of the health relevance of short term and long-term exposures has not been reported for NO₂.

Some studies have documented that subjects living close to busy roads experience more short- term and long-term effects of air pollution than subjects living further away. In urban areas, up to 10% of the population may be living at such “hot spots”. The public health burden of such exposures is therefore significant. Unequal distribution of health risks over the population also raises concerns of environmental justice and equity. More...