Key message
Good

Concentrations of nitrogen dioxide and total nitrogen oxides in ambient air do not exceed the prescribed limit values. Consequently, they are not harmful for human health and vegetation.


This indicator shows the frequency of exceeding of the hourly human health limit value for NO2 concentration, mean annual NO2 concentrations that are also important for human health (annual limit value 40 μg/m3) and NOx concentration (plant protection critical value 30 µg/m3) at measuring sites throughout Slovenia in the period 1992–2016. As monitoring of the plant protection critical value is relevant in the natural environment, the Zavodnje, Kovk and Vnajnarje measuring sites are representative for its monitoring.

Nitrogen oxides (the sum of nitrogen monoxide and nitrogen dioxide concentrations) play an important role in the impact of polluted air on the environment, especially through acidification and eutrophication (excessive amount of nutrients in water bodies) as well as formation of photochemical smog. The main sources of nitrogen oxides are traffic, small heating units and thermal power plants using fossil fuels. Nitrogen oxides are formed when nitrogen combines with oxygen at high temperatures. The percentage of nitric oxide (NO) in exhaust gases is over 90%. In the atmosphere, it gradually oxidises into NO2. The rate of transport-related NO oxidation into higher oxides increases with its distance from the emission source. The presence of ozone in outdoor air greatly accelerates the oxidation reaction. Participation of ozone molecules in the oxidation reaction may reduce the concentration of ozone harmful to humans. Therefore, concentrations of ozone are usually lower along busy roads. In addition to traffic, which causes an increase in NO2 concentrations at traffic measuring sites during morning and evening hours and on workdays, meteorological conditions (especially solar radiation, temperatures and seasons of the year) also affect NO2 concentrations.


Charts

Figure ZR06-1: Number of hours with an exceeded average of 1-hour limit concentration of NO2 (200 µg/m3) (permitted exceeding is 18 hours)
Sources:

Air quality monitoring database (DMKZ), Slovenian Environment Agency, 2020.

Note:

Note to Figure ZR6-1: The measuring station Ljubljana center, which is operated by the Municipality of Ljubljana, has moved from its location at the intersection of Figovec to Vošnjak and Tivoli streetsat at the end of 2009. The station was renovated in accordance with the requirements of the law. 

np = no data

Show data
Urban background[number of hours] Ljubljana Bežigrad[number of hours] Celje[number of hours] Nova Gorica[number of hours] Koper[number of hours] Suburban background[number of hours] Trbovlje[number of hours] Urban-traffic type[number of hours] - Ljubljana center[number of hours] - Maribor center[number of hours] Rural/Agricultural type[number of hours] Murska Sobota - Rakičan[number of hours] permitted exceedance[number of hours]
1992 5 0 5 0 0 0 0 15 15 0 0 0 18
1993 9 0 9 0 0 0 0 21 21 3 0 0 18
1994 14 0 14 0 0 0 0 2 0 2 0 0 18
1995 6 0 6 0 0 0 0 0 0 0 0 0 18
1996 1 0 1 0 0 0 0 0 0 0 0 0 18
1997 0 0 0 0 0 0 0 0 0 0 0 0 18
1998 0 0 0 0 0 0 0 3 3 0 0 0 18
1999 0 0 0 0 0 0 0 2 2 0 0 0 18
2000 0 0 0 0 0 0 0 7 0 7 0 0 18
2001 0 0 0 0 0 0 0 0 0 0 0 0 18
2002 0 0 0 0 0 0 0 0 0 0 0 0 18
2003 0 0 0 0 0 0 0 0 0 0 0 0 18
2004 0 0 0 0 0 0 0 0 0 0 0 0 18
2005 0 0 0 0 0 0 0 0 0 0 0 0 18
2006 0 0 0 0 0 0 0 1 0 1 0 0 18
2007 0 0 0 0 0 0 0 2 0 2 0 0 18
2008 0 0 0 0 0 0 0 0 0 0 0 0 18
2009 0 0 0 0 0 0 0 0 0 0 0 0 18
2010 0 0 0 0 0 0 0 7 7 0 0 0 18
2011 0 0 0 0 0 0 0 0 0 0 0 0 18
2012 0 0 0 0 0 0 0 1 0 1 0 0 18
2013 0 0 0 0 0 0 0 0 0 0 0 0 18
2014 0 0 0 0 0 0 0 0 0 0 0 0 18
2015 0 0 0 0 0 0 0 0 0 0 0 0 18
2016 0 0 0 0 0 0 0 0 0 0 0 0 18
2017 0 0 0 0 0 0 0 1 1 0 0 0 18
2018 0 0 0 0 0 0 0 0 0 0 0 0 18
2019 0 0 0 0 0 0 0 0 0 0 0 0 18
Figure ZR06-2: Annual average concentration of NO2 (annual limit value is 40 µg/m3) 
Sources:

Air quality monitoring database (DMKZ), Slovenian Environment Agency, Air quality monitoring database of Thermal power plant Šoštanj, Trbovlje and TE-TO Ljubljana, Insitute Milan Vidmar, 2020.

Note:

Note to Figure ZR6-2: Measuring Station Ljubljana center, which is operated by the Municipality of Ljubljana, has moved from its location at the intersection of Figovec to Vošnjak and Tivoli streets at the end of 2009. The station was renovated in accordance with the requirements of the law. Data for the new station Ljubljana center will be available from 2010.

np = no data

Show data
Urban background[µg/m3 ] Ljubljana Bežigrad[µg/m3 ] Celje[µg/m3 ] Nova Gorica[µg/m3 ] Koper[µg/m3 ] Suburban background[µg/m3 ] Trbovlje[µg/m3 ] - Škale[µg/m3 ] Urban-traffic type[µg/m3 ] Ljubljana center[µg/m3 ] Maribor center[µg/m3 ] Rural/Agricultural type[µg/m3 ] Murska Sobota - Rakičan[µg/m3 ] Rural/Industrial type[µg/m3 ] - Zavodnje [µg/m3 ] - Kovk[µg/m3 ] - Vnajnarje[µg/m3 ] annual limit value[µg/m3]
1992 32 0 32 0 0 0 0 0 49.50 49 50 0 0 6.50 3 10 0 40
1993 37 0 37 0 0 0 0 0 50 47 53 0 0 6.50 5 8 0 40
1994 37 0 37 0 0 0 0 0 43 41 45 0 0 9.50 11 8 0 40
1995 35 0 35 0 0 0 0 0 38.50 38 39 0 0 10 9 11 0 40
1996 33 0 33 0 0 0 0 0 39 39 39 0 0 3.50 5 2 0 40
1997 0 0 0 0 0 29 29 0 37 36 38 0 0 5 7 4 4 40
1998 29 0 29 0 0 18.50 29 8 40.50 42 39 0 0 6 7 7 3 40
1999 28 0 28 0 0 17 26 8 44 49 39 0 0 7 6 9 5 40
2000 30 0 30 0 0 18 28 8 41 38 44 0 0 6 7 7 4 40
2001 26 0 26 0 0 6 0 6 37 36 38 0 0 6 6 6 5 40
2002 27 29 24 27 0 28 28 0 36 0 36 14 14 6 0 6 6 40
2003 29 32 27 27 0 20 32 8 37 0 37 15 15 5 6 3 5 40
2004 26 29 24 25 0 18 27 9 31 0 31 11 11 8 5 13 5 40
2005 26 27 26 24 0 14.50 24 5 33 0 33 14 14 6 3 10 4 40
2006 27 29 28 24 0 16 23 9 39 0 39 15 15 7 4 12 5 40
2007 25 28 23 25 0 15 22 8 37 0 37 17 17 7 3 12 5 40
2008 25 29 21 30 21 15.50 23 8 34 0 34 16 16 7 3 12 5 40
2009 25 31 22 28 19 13 17 9 32 0 32 14 14 6 4 9 4 40
2010 27.75 35 26 29 21 14 20 8 48.50 63 34 0 0 6 5 9 4 40
2011 26.50 31 25 28 22 12.50 17 8 44.50 55 34 16 16 9 9 11 7 40
2012 23.25 22 27 26 18 12 17 7 42.50 52 33 19 19 8 8 6 10 40
2013 25.25 29 26 25 21 12.50 16 9 37.50 43 32 16 16 10 8 13 9 40
2014 22.50 26 28 19 17 12 17 7 35 40 30 12 12 7.33 7 8 7 40
2015 24.50 30 29 22 17 13 18 8 33.50 36 31 12 13 8 7 8 9 40
2016 22.50 29 22 24 15 13.50 18 9 29.50 32 27 12 12 6.67 5 6 9 40
2017 26.50 30 28 30 18 14.50 21 8 38.50 50 27 12 21 11.50 6 0 17 40
2018 23.75 26 26 25 18 11.50 16 7 22 0 22 12 12 5 5 0 0 40
2019 22.75 25 25 26 15 12.50 19 6 25 0 25 12 13 5 5 0 0 40
Figure ZR06-3: Critical values of NOx for the protection of plants (annual limited value of NOx concentration in the natural environment 30 µg NOx/m3)
Sources:

Air quality monitoring database (DMKZ), Slovenian Environment Agency, Air quality monitoring database of Thermal power plant Šoštanj, Trbovlje and TE-TO Ljubljana, Insitute Milan Vidmar, 2020.

Note:

Note to Figure ZR6-3: Measuring Station Ljubljana center, which is operated by the Municipality of Ljubljana, has moved from its location at the intersection of Figovec to Vošnjak and Tivoli streets at the end of 2009. The station was renovated in accordance with the requirements of the law. Data for the new station Ljubljana center will be available from 2010.

np = no data

Show data
Urban background[µg/m3 ] Ljubljana Bežigrad[µg/m3 ] Celje[µg/m3 ] Nova Gorica[µg/m3 ] Koper[µg/m3 ] Suburban background[µg/m3 ] Trbovlje[µg/m3 ] - Škale[µg/m3 ] Urban-traffic type[µg/m3 ] Ljubljana center[µg/m3 ] Maribor center[µg/m3 ] Rural/Agricultural type[µg/m3 ] Murska Sobota - Rakičan[µg/m3 ] Rural/Industrial type[µg/m3 ] - Zavodnje [µg/m3 ] - Kovk[µg/m3 ] - Vnajnarje[µg/m3 ] annual limit value for protection of vegetation[µg/m3]
1997 0 0 0 0 0 0 0 0 0 0 0 0 7 9 6 5 30
1998 0 0 0 0 0 0 0 0 0 0 0 0 6 8 7 3 30
1999 0 0 0 0 0 9 0 9 0 0 0 0 0 8 7 11 6 30
2000 0 0 0 0 0 29.50 50 9 0 0 0 0 0 9 9 9 30
2001 44 0 44 0 0 8 0 8 68 64 72 0 0 7 8 7 5 30
2002 42 48 37 41 0 35 52 18 61 0 61 19 19 6.50 7 6 30
2003 45 49 44 43 0 32.50 54 11 61 0 61 20 20 6 7 5 6 30
2004 43 46 41 43 0 28.50 47 10 54 0 54 17 17 10 7 17 5 30
2005 43 43 45 41 0 23.50 41 6 60 0 60 20 20 7 5 12 5 30
2006 45 45 46 43 0 24.50 39 10 71 0 71 23 23 8 5 14 5 30
2007 43 45 40 44 0 25.50 38 13 70 0 70 24 24 10 11 14 5 30
2008 42.50 52 40 50 28 25 40 10 63 0 63 22 22 7 6 10 5 30
2009 45 57 47 53 24 23 37 9 61 0 61 20 20 6 5 8 6 30
2010 50.25 64 53 56 28 24.50 40 9 95 122 68 0 0 7.33 7 11 4 30
2011 47 56 47 57 28 21.50 33 10 87.50 105 70 0 0 10.67 11 13 8 30
2012 43.75 47 50 50 28 20.50 32 9 80.50 96 65 28 28 9.33 10 7 11 30
2013 40.50 45 51 45 21 22 34 10 74.50 84 65 21 21 11.33 10 15 9 30
2014 38.50 41 57 35 21 19 29 9 70.50 75 66 17 17 8.67 10 9 7 30
2015 47 56 67 43 22 21.50 33 10 70.50 72 69 17 19 8.67 8 9 9 30
2016 42.25 58 44 45 22 24 37 11 60 58 62 17 20 7.67 6 7 10 30
2017 45 53 51 55 21 27 43 11 84.50 111 58 17 28 14.50 8 0 21 30
2018 39.75 45 47 46 21 17.50 27 8 55 0 55 17 19 6 6 0 0 30
2019 39.25 44 47 48 18 8 8 50 0 50 17 17 6 6 0 0 30

Goals

Compliance with limit values for nitrogen oxides for human health and vegetation protection:

  • 1-hour NO2 limit value for human health protection: 200 μg/m3 (permitted overage: 18-times within a year);
  • annual NO2 limit value for human health protection (in force since 1 January 2011): 40 μg/m3;
  • critical annual concentration for protection and ecosystems in the natural environment: 30 μg/m3.

    The alert threshold for nitrogen oxide concentrations measured over three consecutive hours at locations representative for air quality in an area of at least 100 km2, an entire area or an agglomerated area may not exceed 400 µg/m3.


High concentrations of nitrogen oxide are mostly limited to a narrow band along busy roads and streets. The highest NO2 concentrations are measured at the central Ljubljana traffic measuring site, where the measured values almost reach or exceed the annual limit value. From the perspective of human health, the Ljubljana centre, Maribor centre, Nova Gorica and Celje measuring sites are the most problematic.

Since 1994, NO2 concentration has not been exceeding the legally prescribed hourly limit value for human health protection. Also the annual limit value of 40 µg/m3 has not been exceeded anywhere in Slovenia since 2014.

The annual limit NOx concentration for the protection of vegetation and allowable in the natural environment has not been exceeded in a long time.

As a rule, NO2 concentrations are higher in wintertime, which is largely a result of unfavourable weather conditions (temperature inversion). They are lower during the summer since NO2 is used for the formation of ozone and because wind conditions are more favourable. Elevated NO2 concentrations are mostly measured along busy roads. The NO2 concentration decreases the further away you get from busy roads. Thanks to the introduction of catalytic converters in cars, NO2 emissions from transport have decreased; however, the decrease was not substantial, due to the permanently increasing volume of traffic. Large thermal power plants that use fossil fuels are another source of nitrogen oxides; however, increased concentrations have not been observed in the vicinity of large thermal power plants in recent years.


Methodology

Date of data source summarization