Ozone concentrations in the Netherlands tested against the standard for public health, 1992-2002
The falling trend in high ozone concentrations means that the Netherlands has remained well within the ozone standard for public health for 2010. The European emissions policy would appear to be bearing fruit.
Ozone concentration on the decrease
The number of days with high ozone concentrations (over 120 µg/m3) fell in 2002 to an average 5 days for the Netherlands as a whole. Most days with high concentrations occurred in the province of Zeeland, the Randstad urban agglomeration and below Eindhoven. The highest number was 9 days. The standard of 25 days has not been exceeded for a long time now. This pattern confirms the indications that high ozone concentrations here and elsewhere in Europe seem to be on the decrease. The most probable cause is the reduction in the emissions in Europe of substances from which ozone is formed (see text box, ozone formation).
The effect of the weather on ozone concentrations
The fluctuation in ozone concentrations is primarily caused by variations in the weather from year to year. More exceedances are measured during years with several fine, sunny days (such as 1994 and 1995) than in years with less sunny weather (such as 1998, which was a relatively wet year). Taking an average for three years reduces the effect of the weather on the ozone concentrations. This makes the effect of the European emissions-reduction policy clearer.
| Ozone formation | |
| Ozone is a natural component of air. It is formed from volatile organic compounds (VOC), carbon monoxide (CO), methane (CH4) and nitrogen oxides (NO and NO2, collectively referred to as NOx) under the catalytic action of sunlight. | |
| Ozone is formed at different levels in space and time. Far from densely-populated areas, ozone is mainly formed by the reaction of CH4 and CO. The increase in the amounts of these substances in our atmosphere in recent years may be contributing to the rise in the background level of ozone in the Northern Hemisphere. | |
| In densely-populated areas, excessive emissions of NOx and VOC are the main contributors to ozone formation. Under certain atmospheric conditions (sunlight, high temperature, little wind) this process is responsible for photochemical smog (summer smog). In these circumstances, average hourly ozone concentrations may rise to over 200 µg/m3. | |
| On average, the highest concentrations of ozone in the Netherlands are found in the south and east. The highest concentrations are found there because of the proximity of densely-populated and highly-industrialised areas with high emissions of VOC and NOx. These are the Randstad urban agglomeration and areas in Germany (such as the Ruhr) and Belgium. Ozone from other countries also makes a major contribution to ozone concentrations in the Netherlands. |
Standard for public health
The European standard for exposure of the population to high ozone concentrations (EU, 2002) provides for a target value of 120 µg/m3 for the highest 8-hour average ozone concentration a day. From 2010 onwards, this standard must not be exceeded on more than 25 days a calendar year on average over three years. The objective for the long term, after 2010, is that this target value should not be exceeded on any day.
Link between ozone standard and emissions policy
The EU has linked interim standards for 2010 for ozone concentrations in air to a maximum permitted emission per EU country of the 'ozone-forming' substances VOC and NOx (see text box). If it emerges that the target values and the objectives for the long term are not being achieved, the EU may reduce the permitted maximum for the emissions of VOC and NOx.
Technical note
The annual and three-year average number of days with ozone concentrations (highest 8-hour average) above 120 µg/m3 are based on regional measurements from the National Air Quality Measurement Network.
References
- EU (2002). Council Directive 2002/3/EC of 12 February 2002 relating to ozone in ambient air (link to PDF file). (Third daughter directive) Official Journal of the European Communities No L 67/14.
- RIVM (2003). Data based on measurements from the National Air Quality Measurement Network; processed by the Netherlands Environmental Assessment Agency. RIVM, Bilthoven.
Relevant sections and indicators in the Environmental Data Compendium
- Ozone concentrations in the Netherlands tested against the standard for vegetation, 1992-2002
- Dutch air quality: policy
- Concentration of greenhouse gases, 1980-2002
- Guide to Environmental theme of Acidification and transboundary air pollution
- Health effects in the Netherlands of particulate matter and ozone, 2000
- Zomersmog bulletin 2002
Relevant information outside of the Environmental Data Compendium
- More information about concentrations of substances in the air can be found on the site of the National Air Quality Measurement Network.
- RIVM (2001). Jaaroverzicht luchtkwaliteit 1998 en 1999. RIVM, report 725 301 006, Bilthoven.
- RIVM (2002). Jaaroverzicht luchtkwaliteit 2000. RIVM, report 725 301 008, Bilthoven.
- RIVM (2002). Jaaroverzicht luchtkwaliteit 2001. RIVM, report 725 301 009, Bilthoven.
- Information about current and future developments relating to local air pollution can be found in the Environmental Balance 2003 and the National Environmental Outlook 2000-2030.
