[ZR07]
Air pollution with ozone
Assessments published: [ 2008 2013 ]
The indicator shows the frequencies in the exceeding the target ozone value and the ozone alert threshold per calendar year. The target value for 2010 is set according to the World Health Organisation guidelines for Europe (Fact Sheet No 187, WHO's 1999 Guidelines for Air Pollution Control). It is determined in such a way that the highest average 8-hour running value is calculated from 1-hour concentrations for each day. The highest 8-hour concentration of ozone may not exceed 120 μg/m3 for more than 25 days per year (calculated as a three-year average). The alert threshold is defined as 1-hour concentration higher than 180 μg/m3. This value, as well, is set according to the World Health Organisation guidelines for Europe. It is intended for the protection of human health from short-term exposure to high concentrations of ozone. With such a high level of concentration there is a need to start warning the population of excessive ozone concentrations. The alert value is set at 240 μg/m3; however, during the last decade it has rarely been reached in Slovenia.
Image ZR7-1: Number of days with exceeded target value for ozone in Slovenian urban areas with highest average 8-hour floating value > 120 μg/m3 (annual limit value 25 days)

Source: Automatic Air Quality Measurement Database (ANAS), Environmental Agency of the Republic of Slovenia, 2008


Image ZR7-2: Number of days with exceeded warning value for ozone in Slovenian urban areas (highest 1-hour value > 180 μg/m3)

Source: Automatic Air Quality Measurement Database (ANAS), Environmental Agency of the Republic of Slovenia, 2008


Image ZR7-3: Parameter AOT40

Source: Automatic Air Quality Measurement Database (ANAS), Environmental Agency of the Republic of Slovenia, 2008


In accordance with the Decree on Ozone in Ambient Air (OJ RS, No 8/03) containing the provisions from Directive 2002/3/EC, our objective is that by 2010, no monitoring site will indicate exceedance of both target and alert threshold values. These values are determined with a view to protect human health from long-term exposure to high ozone concentrations.

Being a product of photochemical reactions, tropospheric ozone differs from certain other pollutants. Its precursors, especially nitrogen oxides, are substances forming ozone through the above mentioned photochemical reactions. In Slovenia, transport is regarded to be the greatest source of ozone precursors, accountable for about two thirds of them. Ozone concentrations exhibit an explicit annual curve which is strongly connected with the mode of ozone formation requiring an adequate amount of sunlight. Another crucial contributor to the ozone formation is a long-range (transboundary) transport as the Po Valley in Italy is one of the areas in Europe producing the greatest amounts of ozone.

The data do not display a clear trend. Levels of ozone concentrations are determined by emissions of ozone precursors as well as spring and summer weather conditions, and are subject to change year on year. The year 2003 was extremely hot summer with a lot of solar radiation, which caused strong deviation from other years concerning air pollution with ozone.

Slovenia is divided into areas by different levels of air-pollution threat. With regard to ozone, all areas fall within the lowest quality class, as the ozone concentrations exceed the target values throughout the country, including its rural and mountainous areas. The most polluted area in Slovenia is the Primorska region due to ozone transport from the Po Valley.

With the exception of the monitoring site in Velenje, which is part of information system managed by the TE Šoštanj, all the data are taken from the Automatic air quality measurement database (ANAS) maintained by the Monitoring Office (Environmental Agency of the Republic of Slovenia). The data from individual monitoring sites are not directly comparable due to different types of locations with regard to the influence of pollution sources. The Ljubljana, Celje, Velenje and Nova Gorica monitoring sites are not directly affected by the influence of traffic-related emissions. The Maribor and Trbovlje monitoring sites are placed at roadside locations, where ozone reacts with nitrogen oxides from exhaust gases, thus causing the indices of ozone concentrations to be appreciably lower. The monitoring site in Hrastnik is located at the verge of the urban area; in the event of south-western winds it is exposed to the influence of flue gases from the Trbovlje Thermal Power Plant, which may also have a lowering effect on ozone concentrations.

Although provided by a smaller number of monitoring sites, the data on ozone concentrations have otherwise been available since 1992. The number of monitoring sites increased in 2002.

In order to illustrate the trend, the exceedances of target and alert threshold values are also shown for previous years, according to the current Decree on ozone in ambient air, since the limit values as determined in formerly applicable regulations are not comparable with the present target and alert threshold values.

14. November 2008

Apology: Texts in English haven't been updated yet.

Anton Planinšek, Environmental Agency of the Republic of Slovenia