II.4.2.2 Air quality with regard to the limit values for the protection of ecosystems and vegetation

In addition to the limit values for the protection of health the national legislation introduced, in compliance with EU Directives, also the limit values for the protection of ecosystems and vegetation. The survey of the limits is presented Chapter II.3.

II.4.2.2.1 Sulphur dioxide

In 2011 neither the limit value for the annual average concentration nor the limit value for the winter average concentration were not exceeded in rural localities. The situation from the previous year with the exceedance of the limit value for the winter average 2010/2011 in the locality Komáří Vížka did not repeat. The highest winter average concentration in 2011 was recorded in the locality Lom (17.6 μg.m^-3), the annual average concentration reached its maximum in the locality Komáří Vížka (17 μg.m^-3).

After the year 1998 there was recorded, in connection with coming into force of the Act No. 309/1991 Coll., and meeting the required emission limit values, a marked decrease of SO₂ concentrations. Since then the annual average SO₂ concentrations have not exceeded the set limit value 20 μg.m^-3 at rural stations (Fig. II.4.2.51). In 2008 there was further decrease of air pollution caused by SO₂ on the whole territory of the Czech Republic, in 2009 and 2010 the slight increase of annual average was recorded at most stations. In 2011 both the annual and winter average concentrations decreased again in two thirds of localities as compared with the previous year, and, on the contrary, they slightly increased in one third of the localities.
The map was constructed from the data of all background stations measuring SO₂ with regard to their classification; only rural stations are marked with spot symbols.

The results of SO₂ air pollution monitoring with regard to the limit values for the protection of ecosystems and vegetation for the annual and winter periods are shown in the Tables II.4.2.22 and II.4.2.23 and in Figs. II.4.2.53 and II.4.2.54.

This chapter is closed by the graphs of courses of 24-hour SO₂ concentrations at selected stations, related to the limit value for the winter and annual averages (Figs. II.4.2.55 and II.4.2.56).

Tab. II.4.2.22 Stations with the highest values of annual averages of SO₂ concentrations at rural stations

Tab. II.4.2.23 Stations with the highest values of winter averages of SO₂ concentrations at rural stations, 2011/2012

Fig. II.4.2.51 Annual average concentrations of SO₂ in 2001–2011 at selected rural stations

Fig. II.4.2.52 Winter average concentrations of SO₂ in 2001/2002–2011/2012 at selected rural stations

Fig. II.4.2.53 Field of annual average concentration of SO₂ in 2011

Fig. II.4.2.54 Field of average concentration of SO₂ in the winter period 2011/2012

Fig. II.4.2.55 24-hour concentrations at the stations with the highest annual concentrations of SO₂ in 2011

Fig. II.4.2.56 24-hour concentrations at the stations with the highest winter concentrations of SO₂ in the winter period 2011/2012

II.4.2.2.2 Nitrogen oxides

In 2011 the NO_x air pollution limit value for annual average concentrations (30 μg.m^-3) was not exceeded in any of 42 localities classified as rural (Tab. II.4.2.24 and Fig. II.4.2.57). Both the table and the map for NO_x include also the rural stations measuring only NO₂, because as concerns the rural stations, it can be estimated that NO_x concentrations correspond approximately to NO₂ concentrations, in other words, the difference between both concentrations is negligible.

In 2011 the number of rural stations at which the annual average NO_x concentrations decreased was slightly higher (24) than the number of those at which it increased (17 localities) (Fig. II.4.2.57).

The construction of the map of the spatial distribution of annual average NO_x concentrations is based on the combination of measurement and modelling. All stations measuring NO_x including the rural station measuring NO₂ were used for the construction of the map of the field of NO_x, and also the current data on emissions from mobile sources in the Czech Republic were regarded. The higher NO_x concentrations can occur also in the vicinity of local communications in the villages with intensive traffic and dense local transport network, where there is no measurement of concentrations. The spot symbols highlight only the rural stations (Fig. II.4.2.58) because the level of annual NO_x concentrations in these localities is evaluated with regard to the limit value.

This chapter is closed by the graphs of courses of 24-hour NO_x concentrations for the selected localities with higher annual averages of NO_x concentrations in 2011 (Fig. II.4.2.59).

Tab. II.4.2.24 Stations with the highest values of annual average of NO_x and NO₂ concentrations at rural stations

Fig. II.4.2.57 Annual average concentrations of NO_x and NO₂ in 2001–2011 at selected rural stations

Fig. II.4.2.58 Field of annual average concentration of NO_x in 2011

Fig. II.4.2.59 24-hour concentrations at the stations with the highest annual concentrations of NO_x in 2011

II.4.2.2.3 Ground-level ozone

For the assessment of vegetation protection against ozone exceedances the national legislation uses, in compliance with the respective EU Directive, the exposure index AOT40¹.

Of the total number of 37 rural and suburban stations for which the AOT40 calculation is relevant according to the legislation, the target value for ozone for the protection of vegetation was exceeded in 8 localities in 2011 (the average for the years 2007–2011). The highest value was recorded in the locality Štítná n.Vláří (20,801.5 μg.m^-3.h).The survey of stations with the highest values of AOT40 is given in Table II.4.2.25.

As compared with the previous assessment for the period 2006–2010, the number of localities with exceedances slightly decreased (from 20 to 8). The decrease of the value of the AOT40 exposure index for the year 2011 as compared with the year 2010 was recorded in comparable number of localities (19 localities) as its increase (15 localities).

The comparison of the temperatures of the period April–September 2006 (which was not included in the assesssed five-year period) and the year 2011 shows that there was recorded the marked decrease of the average temperature in July 2011 (by 5� C), in April and August, on the contrary recorded its slight increase. In the average, the temperatures increased by 0.6 � in this period of 2011. On the contrary, the maximum temperatures in 2011were lower at almost three quarters of localities in comparison with the year 2006 and similarly, the levels of the sum of daily averages of global solar radiation were lower in ca 65 % of localities monitoring the given parameter. Air pollution concentrations of precursors showed similarly as meteorological parameters various trends. While NO₂ concentrations decreased in 2011 as compared with the year 2006 in most localities, the concentrations of 30 substances included in the VOC group, monitored in Košetice and in Libuš, slightly increased in 2011 in more than 60 % of them. With regard to rather complicated atmospheric chemical reactions during the creation and disintegration of ozone, to its dependence on the absolute amount and the relative share of its precursors in the ambient air connected also with long-range transport of pollutants, as well as on meteorological conditions, it is difficult to make more detailed comments on the year-to-year changes.

The spatial distribution of AOT40 exposure index for the 2011 assessment is shown in Fig. II.4.2.62. Fig. II.4.2.60 presents the AOT40 development in average for 5 years in the period 2007–2011 in selected localities. Fig. II.4.2.61 shows the development of AOT40 values calculated for each year in the period 2007–2011. The stations with the highest values of AOT40 exposure index are depicted in Fig. II.4.2.63.

Tab. II.4.2.25 Stations with the highest AOT40 values of ozone at rural and suburban stations

Fig. II.4.2.60 Annual values of ozone exposure index AOT40 in 2001–2011 at selected stations, average for 5 years

Fig. II.4.2.61 Annual values of ozone exposure index AOT40 in 2007–2011 at selected stations

Fig. II.4.2.62 Field of exposure index AOT40 values, average for 5 years, 2007–2011

Fig. II.4.2.63 Stations with the highest exposure index AOT40 values in recent 5 years, 2007–2011

¹AOT40: accumulated exposure is calculated as the sum of the difference between hourly ozone concentrations and the threshold level of 80 μg.m^-3 (= 40 ppb) for each hour when this threshold value was exceeded. Pursuant to the requirements of the Government Order No. 597/2006 Coll. AOT40 is calculated for the period of three months (May to July) measured between 8:00 and 20:00 Central European Time (= 7:00 and 19:00 UTC).