II.4.1 Agglomerations

With regard to the Communication of the Air Quality Protection Division of the Ministry of Environment on delineating zones and agglomerations within the territory of the Czech Republic, air quality assessment in the proposed agglomerations (Prague, Brno and the Moravian-Silesian Region) has been treated with more attention since 2005. In addition to the above agglomerations, special attention is paid in this Yearbook also to the zone Ústí nad Labem Region due to the concentration of industrial plants, higher population density and also due to the recorded above-the-limit concentrations of pollutants.

II.4.1.1 Prague

The Capital City of Prague is the area in which a lot of people are exposed to ambient air pollution. Most of the limit values exceedances are connected with significant traffic loads ensuing from the fact that the main routes lead directly through the city centre.

In 2008 the PM₁₀ particles concentrations were monitored in Prague in 15 CHMI localities and in 7 ZÚ localities. The most frequent exceedances of 24-hour PM₁₀ limit value (50 μg.m^-3) were recorded in the following localities: Prague 2-Legerova (84x), Prague 5-Smíchov (67x) and Prague 5-Mlynářka (43x). The tolerated number of exceedances is 35. All three cases are the localities with very heavy traffic loads. Of the total number of 19 localities with valid annual average (with sufficient number of measurements with regard to the requirement of minimum data collection) 5 stations recorded 24-hour PM₁₀ limit value exceedances. The annual PM₁₀ limit value (40 μg.m^-3) was exceeded only in the locality Prague 5-Svornosti (41 μg.m^-3).
The PM_2.5 particles concentrations were measured in 5 CHMI localities and in 1 ZÚ locality in 2008. In spite of the fact the valid air pollution limit value for PM_2.5 has not been set in the Czech legislation so far, the comparison of the measured concentrations with the target limit value for annual average concentration set by the Directive of the European Parliament 2008/50/EC (25 μg.m^-3) is very interesting. The highest average annual concentrations in Prague localities were as follows: Prague 5-Smíchov 21 μg.m^-3, Prague 10-Šrobárova 20 μg.m^-3 and Prague 4-Libuš 18 μg.m^-3. It is quite evident that the target value for PM_2.5 fraction set by the Directive 2008/50/EC was not exceeded at any Prague station.
The graphs in Figs. II.4.1.1, II.4.1.2 and II.4.1.3 show the annual course of monthly PM₁₀ and PM_2.5 concentrations, numbers of exceedances of 24-hour PM₁₀ limit value and monthly PM_2.5/PM₁₀ ratios in 2008.

The highest number of exceedances of the 24-hour limit value of PM₁₀ (50 μg.m^-3) was recorded in November in the locality Prague 5-Smíchov. The highest average monthly PM₁₀ concentration was recorded in February in the locality Prague 5-Mlynářka (58 μg.m^-3) and the highest average monthly PM_2.5 concentration also in February in the locality Prague 9-Vysočany (36 μg.m^-3).

The PM_2.5/PM₁₀ ratio at 5 stations in Prague (where PM_2.5 and PM₁₀ are measured simultaneously) ranged from 0.3 (February: Prague 5-Mlynářka) to 0.9 (December: Prague 4-Libuš). NO₂ concentrations were measured in all 22 localities in Prague in 2008. The AMS station Prague 2-Legerova (hot spot) which is located in the immediate vicinity of a communication with heavy traffic, exceeded the hourly NO₂ limit value plus the margin of tolerance (200+20 μg.m^-3). The value of 200 μg.m^-3 was exceeded 106x, the value of 220 μg.m^-3 was exceeded 38x. .The tolerated number of exceedances is 18. The highest 19th hourly concentration at this AMS reached 280μg.m^-3. As concerns other localities, there was also one exceedance of the hourly NO₂ concentration 200 μg.m^-3 in 2008, and namely at the station Prague10-Průmyslová, which is also significantly influenced by traffic.

The annual air pollution limit value plus the margin of tolerance for NO₂ (40+4 μg.m^-3) was exceeded in the following localities: Prague 5-Svornosti (79 μg.m^-3), Prague 8-Sokolovská (67 μg.m^-3), Prague 2-Legerova (66 μg.m^-3), Prague 1-Národní muzeum (52 μg.m^-3) and Prague 5-Smíchov (46 μg.m^-3).
It can be expected that the exceedance of air pollution limit values can occur also in other localities exposed to traffic, where there are no measurements.

Fig. II.4.1.6 shows the graphs of annual courses of monthly NO₂ concentrations at selected localities in Prague in 2008. Groups of stations with similar courses of NO₂ concentrations are visible in the figure. They are related to the traffic loads at individual localities. The first group is represented by three stations Prague 2-Legerova (hot spot) and two ZÚ stations Prague 5-Svornosti and Prague 8-Sokolovská that are also situated in the immediate vicinity of the communication. NO₂ concentrations exceed the limit value at these localities in the whole yearly course. It is followed by the second group of localities also markedly influenced by traffic, with similar courses of the levels ranging around the limit value (Prague 9-Vysočany, Prague 8-Karlín and Prague 5-Smíchov), and finally there are two localities (Prague 2-Riegrovy sady and Prague 4-Libuš) representing urban background where the influence of traffic is not as high and the measured concentrations are below the limit value.

Another problem is caused by above-the-limit benzo(a)pyrene concentrations which exceeded the target value in two of three localities which measured it in Prague, and namely Prague 10-Šrobárova and Prague 5-Smíchov. The Prague 4-Libuš locality recorded the annual average equal to the level of the limit value.
The results of the measured concentrations of PM₁₀, NO₂ and benzo(a)pyrene suggest the serious need to find the solution for the traffic situation within the agglomeration.

In Prague, at the station Prague 5-Řeporyje, where the annual average arsenic concentration has increased gradually during the recent four years, the target value was exceeded for the first time in 2007 (for the recent 11 years). The annual average reached the level 6.7 ng.m^-3. The exceedance of the target value of the average annual concentration in this locality was recorded also in 2008. The annual average increased again and reached the maximum for the whole Czech Republic in 2008 (9.2 ng.m^-3).

The exceedances of the target value for the ground-level ozone was also recorded. It was exceeded in 3 of 8 localities in Prague, which have carried out the measurements in the recent three years at least for the period of one year (pursuant to the definition of the target value in the Government Order). The exceedance was recorded in the following localities: Prague 6-Suchdol, Prague 4-Libuš and Prague 5-Stodůlky.

Fig. II.4.1.1 Annual course of monthly PM₁₀ concentrations and number of 24-hour PM₁₀ limit exceedances, Prague agglomeration, 2008

Fig. II.4.1.2 Annual course of monthly PM_2.5 concentrations, Prague agglomeration, 2008

Fig. II.4.1.3 Monthly PM_2.5/PM₁₀ proportions, Prague agglomeration, 2008

Fig. II.4.1.4 Annual course of monthly benzo(a)pyrene concentrations, Prague agglomeration, 2008

Fig. II.4.1.5 Annual course of monthly O₃ concentrations, Prague agglomeration, 2008

Fig. II.4.1.6 Annual course of monthly NO₂ concentrations at selected AMS stations, Prague agglomeration, 2008

Fig. II.4.1.7 Field of the annual concentration of NO₂, Prague agglomeration, 2008

Fig. II.4.1.8 Field of the annual concentration of benzo(a)pyrene, Prague agglomeration, 2008

II.4.1.2 Brno

Air pollution monitoring network
In 2008 the Brno agglomeration carried out air quality measurements at 12 stations of air pollution monitoring owned by 3 institutions: Czech Hydrometeorological Institute (air pollution monitoring incl. sampling accredited according to ČSN EN ISO/IEC 17025:2005), the Municiple Council of the city of Brno and the Health Institute in Brno.

The estimate of the size of polluted areas
The 24-hour limit value for PM₁₀ is constantly exceeded in the territory of the Brno agglomeration. The largest area of the agglomeration affected by the increased concentrations was recorded in 2005, the lowest coverage was measured in 2004. The marked increase of the share of the territory with the exceeded 24-hour limit value for PM₁₀ in 2005 and 2006 was caused mainly by meteorological conditions (long cold winter 2005/2006, frequent occurrence of temperature inversions etc.) and the related anthropogenic activities (longer heating season, the necessity of road spreading, cold starting of the cars etc.). Similar situation occurred after the year 2002. In addition to the 24-hour limit value also the limit value for the average annual PM₁₀ concentration was exceeded. In 2008 the limit value for the average annual concentration was exceeded in traffic localities Brno-Úvoz (hot spot) and Brno-Svatoplukova. The limit value for 24-hour concentration was exceeded again in traffic localities Brno-Úvoz (hot spot), Brno-Svatoplukova, Brno-Zvonařka, Brno-Výstaviště, Brno-střed and Brno-Masná. On the contrary, for the first time since 2002 there has not been any exceedance of the 24-hour limit value at the background station Brno-Tuřany. The highest concentration of the PM_2.5 particles, for which the limit value 25 μg.m^-3 will come into force in 2010, are also measured mainly in traffic localities. If the limit value was valid already in 2008, the exceedance would occur in the following localities: Brno-Svatoplukova, Brno-Zvonařka and Brno-Výstaviště. The remaining locality Brno-Tuřany with its average annual PM_2.5 concentration (19 μg.m^-3) would not exceed the mentioned limit value. The above facts suggest that the exceedance of the limit values for PM₁₀ in the Brno agglomeration has its most significant contribution in traffic.

In the recent years the number of exceedances of the annual average NO₂ concentration has also increased. The limit value exceedances occurred at traffic stations, whose number has increased thanks to the stations of the Municipal Council of the city of Brno and the station Brno-Úvoz (hot spot). It can be therefore expected that the limit value could be exceeded in these localities also in the previous years. The increased concentrations are contributed by the increased intensity of traffic and also by meteorological conditions. In 2008 the localities Brno-Svatoplukova and Brno-Úvoz (hot spot) exceeded the LV+MT, the locality Brno-střed recorded the level closely above the limit value. As for the hourly limit value most localities in the Brno agglomeration ranged between the lower and upper assessment thresholds in 2008.

Other limit values for SO₂, CO, Pb and benzene are not exceeded in the Brno agglomeration, on the contrary, the concentrations of individual pollutants, except of benzene, range below the lower assessment threshold. Thus the number of selected measurements was limited in the Brno agglomeration – particularly SO₂ – the measurements were abolished in the localities Brno-Kroftova and Brno-střed.

In the territory of the Brno agglomeration also the target values for tropospheric ozone and benzo(a)pyrene are exceeded. Tropospheric ozone exceeds the target value in the whole territory of the agglomeration, but the results are not practically different from those in remaining part of the Czech Republic.

Benzo(a)pyrene is one of the polycyclic aromatic hydrocarbons (PAH), originating mainly by the combustion of solid and liquid fuels. The increased concentrations of benzo(a)pyrene in the Brno agglomeration can thus be expected mainly in the vicinity of the major line sources. At present benzo(a)pyrene is measured in 2 localities in the Brno agglomeration and both of them exceed the limit value. The station Brno-Masná (background type), situated, however in the locality strongly influenced by traffic, the concentration reached 1.4 μg.m^-3., the locality Brno-Kroftova 1.3 μg.m^-3. The dispersion study processed for the Municipal Council shows that the most loaded area as concerns benzo(a)pyrene concentrations is situated in the vicinity of the large Brno ring road in the locality Zvonařka and near the Brno main railway station.
The remaining pollutants with the set target values (heavy metals arsenic, cadmium and nickel) have been reaching the concentrations only below the lower assessment threshold during several latest years.

The trend of concentrations of major pollutants in 2008
The pollutants exceeding the limit values or the target value were selected to show more detailed development of the concentrations, and namely PM₁₀ (and PM_2.5) particles, NO₂, benzo(a)pyrene and tropospheric ozone.
In case of average annual PM₁₀ concentrations individual types of stations were averaged and compared with the regional background station Mikulov-Sedlec. Fig. II.4.1.9 shows clearly that there is relatively good correlation between the trends of concentrations from background stations and the regional background station. The trend, as compared with the traffic stations, differs just in the year 2008, when the background stations together with the station Mikulov-Sedlec recorded the decrease of concentrations as compared with the year 2007. Traffic stations recorded a slight increase. This, however, may be caused by the increase of the number of traffic stations, and mainly by launching the measurements at the station Brno-Úvoz (hot spot). As for the absolute concentrations, the highest concentrations are measured in traffic localitites, the Brno background localities have lower concentrations (by about 5–10 μg.m^-3) and regional background station Mikulov-Sedlec reaches the lowest concentrations (by about 2–6 μg.m^-3 lower than the Brno background concentrations).

The average monthly PM₁₀ concentrations in individual stations in the Brno agglomeration are depicted in Fig. II.4.1.10. The figure shows the apparent convex course of concentrations during the calendar year, the maximum values are thus reached at the beginning and at the end of the year, the minimum concentrations in the middle of the year. Fig. II.4.1.11 is based on averaging the traffic and background stations and adding the regional background station Mikulov-Sedlec and the function of temperature. It is apparent that the average monthly PM₁₀ concentration is inversely related to the air temperature. Further, during the summer months the background of the city of Brno is comparable with the regional background, in the winter months the background concentrations in Brno are approx. by 5–13 μg.m^-3 higher. The average monthly concentrations at traffic stations in the Brno agglomeration are approx. by 5–15 μg.m^-3 higher.
The fine fraction PM_2.5 was measured at 4 station in the Brno agglomeration in 2008 – 3 traffic and 1 background. All traffic stations would exceed the limit value for the average annual PM_2.5 concentration 25 μg.m^-3. On the contrary, the background locality Brno-Tuřany would not exceed this limit. The average monthly shares of PM_2.5 in PM₁₀ are depicted in Fig. II.4.1.12. It is apparent that the share of PM_2.5 in PM₁₀ has also the convex character. The slightest result is achieved in the background locality Brno-Tuřany, where the interval PM_2.5 in PM₁₀ ranges from 68 to 80 %. This locality, as the only one, uses radiometry (accredited according to ČSN EN ISO/IEC 17025:2005), and moreover, two separate instruments. In other remaining traffic stations the convex character is more apparent. These stations measure all particle fractions by one apparatus using the optoelectronic method (orthogonal nephelometry).

The average monthly concentrations of NO₂ (Fig. II.4.1.13) are to a certain extent dependent on the locality disposition – traffic localities are exposed to the highest air pollution loads of NO₂ due to emissions from traffic, which in case of NOx represent about 80 % in the Brno agglomeration. After the averaging of traffic and background localities, incl. the comparison with the regional background locality in Mikulov-Sedlec and the temperature, the highest loads were confirmed in traffic localities (Fig. II.4.1.14). The graph shows clearly that the background concentrations in Brno are approx. by 10 μg.m^-3 higher than the regional background, air pollution load in the localities exposed to traffic is by another 15–20 μg.m^-3 higher than the background of the Brno agglomeration.

Benzo(a)pyrene is measured only in two localities in the Brno agglomeration. The average monthly concentrations in these two localities are, together with the average monthly temperatures, depicted in Fig. II.4.1.15. At the beginning of the year higher concentrations were measured in the traffic locality Brno-Kroftova, at the end of the year, markedly higher concentrations were recorded at the station Brno-Masná, classified as a background station, but situated in the locality with strong traffic influence near the large Brno ring road. In summer the concentrations at both stations were comparable.

Tropospheric ozone exceeds the limit value set by the Government Order No. 597/2006 Coll. in most part of the territory of the Czech Republic. In the Brno agglomeration the coverage is in fact 100 %; the exceedances occur mainly in summer as there are most suitable conditions for photochemical creation of tropospheric ozone from NO₂ and VOC. These photochemical reactions are influenced by solar radiation (necessary for the reactions). The graph in Fig. II.4.1.16 presents the average monthly concentrations of tropospheric ozone in traffic and background localities of the Brno agglomeration, the comparison with the regional background station in Mikulov-Sedlec and the average monthly values of solar radiation in W/m². Unlike the previous pollutants the highest concentrations are measured in the locality Mikulov-Sedlec, the concentrations measured at the background localities are roughly by 5–10 μg.m^-3 lower, and the lowest concentrations are measured in traffic localities (by another 10–15 μg.m^-3 lower). These differences are connected with ozone reactivity, i.e. with the amount of possible reactants in the ambient air. Ozone is a very strong oxidation agent which easily reacts with a lot of compounds in the ambient air, incl. the pollutants (as for instance NO emitted by the traffic), and therefore in the localities with the highest pollutants� concentrations ozone is able to react much more intensively (and thus reduce its concentration in the ambient air). This is the reason why the lowest concentrations of tropospheric ozone are measured in traffic localities and the highest ones, on the contrary, in the localities not much influenced by the pollutants.
The above facts show that the Brno agglomeration has its delineated areas with deteriorated air quality, mainly due to high traffic intensity. The traffic localities record the exceedances of the limit value for PM₁₀, NO₂ and target value for benzo(a)pyrene. The draft and the implementation of the measures aimed at the transport and the line sources should be the priorities for the solution of the problem of ambient air quality in the Brno agglomeration.

Tab. II.4.1.1 The development of the limit value (LV) and target value (TV) exceedances in the Brno agglomeration, % of area of the administrative unit, 2001–2008

Fig. II.4.1.9 The average annual PM₁₀ concentrations of individual types of stations, Brno agglomeration, 2005–2008

Fig. II.4.1.10 The average monthly PM₁₀ concentrations, Brno agglomeration, 2008

Fig. II.4.1.11 The average monthly PM₁₀ concentrations of individual types of stations and the average monthly temperature, Brno agglomeration, 2008

Fig. II.4.1.12 The average monthly shares of PM_2.5 in PM₁₀, Brno agglomeration, 2008

Fig. II.4.1.13 The average monthly NO₂ concentrations, Brno agglomeration, 2008

Fig. II.4.1.14 The average monthly NO₂ concentrations of individual types of stations and the average monthly temperature, Brno agglomeration, 2008

Fig. II.4.1.15 The average monthly benzo(a)pyrene concentrations and the average monthly temperature, Brno agglomeration, 2008

Fig. II.4.1.16 The average monthly O₃ concentrations of individual types of stations and the average monthly values of solar radiation, Brno agglomeration, 2008

Fig. II.4.1.17 Field of the annual concentration of NO₂, Brno agglomeration, 2008

Fig. II.4.1.18 Field of the annual concentration of benzo(a)pyrene, Brno agglomeration, 2008

II.4.1.3 The Moravian-Silesian Region

The average annual concentrations measured in 2008 in the Moravian-Silesian Region were comparable with the concentrations measured in 2007. During the both years the measured concentrations were lower than in the previous years owing to very favourable dispersion conditions, only at the end of the year 2008 there was an episode with the increased concentrations of suspended particles in the ambient air. The average values of air pollution in 2008 are comparable with the levels reached in 2000. In 2008 the number of days with the PM₁₀ limit value exceedance decreased as compared with the year 2007; the most marked decrease of PM₁₀ concentrations was recorded at the station Ostrava-Bartovice. (Fig. 4.1.34). In spite of this, there occurred exceedances of the limit values set by the Government Order No. 597/2006 Coll. in the most of the territory of the region.

In the period 12–18 December 2008 the average 24-hour concentrations of suspended particles of PM₁₀ fraction increased in most localities in the Ostrava-Karviná area; they were repeatedly four times higher than the daily limit value 50 μg.m^-3, in several localities the value of the limit was exceeded even seven times (Fig. II.4.1.19). The multiple limit exceedance occurred again on 29–30 December 2008.
Similarly as in the previous years, there are the same problem pollutants: suspended particles of PM_2.5 and PM₁₀ fractions, benzo(a)pyrene, benzene and tropospheric ozone.

Ambient air pollution caused by PM₁₀ suspended particles in the Ostrava-Karviná area
The highest PM₁₀ concentrations and the highest number of days with average 24-hour concentrations higher than the level of the daily limit value 50 μg.m^-3 are reached during the winter months. The average 24-hour concentrations higher than 100 μg.m^-3 occur in the period May–September only sporadically. On average, during the recent ten years there were 116 days with the concentrations exceeding the daily limit value, out of which 24 days with the concentration higher than 100 μg.m^-3. Fig. II.4.1.20 shows the frequency of the average 24-hour PM₁₀ concentrations in the period X/1999–II/2009 based on the measurements at the stations Bohumín, Havířov, Karviná, Orlová, Studénka, Věřňovice and Ostrava (Bartovice, Českobratrská, Fifejdy, Mariánské Hory, Poruba/CHMI, Přívoz, Zábřeh).
The occurrence of high PM₁₀ concentrations is an order higher in cold periods (October–March) than in the summer periods (April–September), which is connected firstly with higher emissions but particularly with worse dispersion conditions (Fig. II.4.1.21 and Fig. II.4.1.22; the difference in meteorological conditions during the winter periods is characterized by the average air temperature and the average wind velocity for the months December–February).

The episodes with the average 24-hour concentrations higher than 100 μg.m^-3 measured simultaneously at several stations occur almost exceptionally in the period October–March. The most frequent episodes last one or two days, in the average there are twelve such episodes during each cold period and 4–5 longer episodes; the one-day and two-day episodes with the average 24-hour concentrations higher than 150 μg.m^-3 occur in average six times and the longer episodes once per one cold period (Tab. II.4.1.2).
During the episodes with high ambient air pollution the meteorological conditions are different from the usual situations. Meteorological characteristics, however, differ also during one-day and several-day episodes; during several-day episodes the air temperature is usually markedly lower and the layering of the boundary layer of the atmosphere is more stable. All episodes are characterized by lower wind velocity and different wind direction. The frequency of the usually prevailing south-west wind markedly decreases during the episodes due to the increased frequencies of northern and eastern winds; also calm, i.e. wind velocity lower than 0.5 m.s^-1 is much more frequent (Fig. II.4.1.23, Fig. II.4.1.24, Fig. II.4.1.25); the data on temperature and wind velocity are supplied from the meteorological stations Mošnov-Ostrava airport (251 m a.s.l.), Červená in Nízký Jeseník Mts. (750 m a.s.l.) and Lysá hora in the Moravskoslezské Beskydy Mts. (1324 m a.s.l.).

Tab. II.4.1.2 The length of the episodes with high ambient air pollution caused by PM₁₀ in the Ostrava-Karviná area for 10 cold periods (October–March), from 1999/2000 to 2008/2009 (except March 2009)

Fig. II.4.1.19 Ostrava during the winter episode with the increased air pollutants' concentrations

Fig. II.4.1.20 The frequency of the average 24-hour PM₁₀ concentrations in the period X/1999–II/2009

Fig. II.4.1.21 The level of PM₁₀ concentrations in the cold parts of the year (October–March)

Fig. II.4.1.22 The level of PM₁₀ concentrations in the warm parts of the year (April–September)

Fig. II.4.1.23 The average air temperature and the average vertical temperature gradient during the episodes with high levels of air pollution in the Ostrava-Karviná area

Fig. II.4.1.24 The average wind velocity during the episodes with high levels of air pollution in the Ostrava-Karviná area

Fig. II.4.1.25 Relative frequencies of wind direction in % during the episodes with high levels of air pollution in the Ostrava-Karviná area

Fig. II.4.1.26 Field of the annual concentration of NO₂, Moravian-Silesian agglomeration, 2008

Fig. II.4.1.27 Field of the annual concentration of benzo(a)pyrene, Moravian-Silesian agglomeration, 2008

II.4.1.4 Other areas with air pollution loads with higher density of population

The Ústí nad Labem Zone

The Ústí nad Labem Region is defined as a zone. This area has high population density and is highly industrialized, and thus a number of pollutants have above-the-limit concentrations.
In 2008, data on pollutants� concentrations were submitted to the ISKO database from the measurements in 43 localities in the Ústí nad Labem Region (21 CHMI, 9 ČEZ, 11 ZÚ, 1 SŠZE Žatec). At several localities the measuring programme was not complete.

PM₁₀ concentrations were measured in 23 localities. The exceedances of the 24-hour limit value for PM₁₀ were measured in 6 localities: Ústí n.L.-město (the LV 50 μg.m^-3 exceeded 54x), Lovosice-MÚ (49x), Lom (59x), Děčín (55x), Ústí n.L.-Všebořická hot spot (50x, in 2007 57x), Most (39x, in 2007 57x). As compared with the year 2007, when the limit value exceedances occurred in 8 localities, the situation has improved. In 2008 the exceedance of the PM₁₀ annual limit value was not recorded at any station in the Ústí nad Labem Region, the highest annual average concentration of PM₁₀ was measured at the station Ústí n. L.-město (33.2 μg.m^-3, in 2007 it was 32.5 μg.m^-3).

PM_2.5 particles were measured in 5 localities in the Ústí nad Labem Region. The highest annual average PM_2.5 concentration was recorded in the locality Most; it reached the value of 17.3 μg.m^-3. This value is below the target value for the annual average concentration pursuant to the Directive 2008/50/EC. In 2008 NO₂ concentrations were measured in 35 localities in total in the Ústí nad Labem Region (out of which 20 CHMI). The station Ústí n.L.-Všebořická, which is significantly influenced by traffic, exceeded the annual limit value of NO₂ but not the limit value plus the margin of tolerance (43.9 μg.m^-3, 2007 42.1 μg.m^-3).

In 2008 the limit value for 24-hour SO₂ concentration was exceeded only in the Ústí nad Labem Region, and namely in the locality Úštěk (1x), the limit value was not exceeded (the tolerated number of LV exceedance – 3x).
The 1-hour limit value of SO₂ was not exceeded, the highest 1-hour value (353 μg.m^-3) was measured at the station Komáří Vížka.

Benzo(a)pyrene concentrations were measured in 5 localities, in one of them the target value for the annual average concentration was exceeded (Ústí nad Labem-ZÚ Pasteurova –1.45 ng.m^-3, in 2007 it was 1.34 ng.m^-3).

The target value for ground-level ozone was exceeded similarly as in other parts of the Czech Republic. Totally the exceedances of the target limit value for the three-year period 2006–2008 were recorded in 5 localities of the total number of 12 localities measuring ground-level ozone in 2008.

Air pollution situation in individual months of the year 2008 at selected stations of the Ústí nad Labem Region is depicted in the graphs in Figs. II.4.1.28–II.4.1.33. The graph in Fig. II.4.1.30 shows the PM_2.5/PM₁₀ ratio at the stations in the Ústí nad Labem Region measuring both fractions. It is apparent that the ratio is changed not only during the year but also according to the station location, and namely from 40.46 (June, rural background station Lom) and 87.48 (rural background station Doksany).

In general the 2008 pollutants� concentrations decreased as compared with 2007, and primarily as compared with the years 2005 and 2006. Similarly as in other parts of the Czech Republic this is due to favourable meteorological, and mainly dispersion conditions, but also due to the decrease of emissions in 2008, when the drop in industrial production began to be felt.

Fig. II.4.1.28 Annual course of monthly PM₁₀ concentrations and number of 24-hour PM₁₀ limit exceedances, Ústí nad Labem Region, 2008

Fig. II.4.1.29 Annual course of monthly PM_2.5 concentrations, Ústí nad Labem Region, 2008

Fig. II.4.1.30 Monthly PM_2.5/PM₁₀ proportions, Ústí nad Labem Region, 2008

Fig. II.4.1.31 Annual course of monthly benzo(a)pyrene concentrations, Ústí nad Labem Region, 2008

Fig. II.4.1.32 Annual course of monthly O₃ concentrations, Ústí nad Labem Region, 2008

Fig. II.4.1.33 Annual course of monthly NO₂ concentrations, Ústí nad Labem Region, 2008

4.1.5 Trends of annual air pollution characteristics of SO₂, PM₁₀ and NO₂ for the period 1996–2008

Fig II.4.1.34 shows the trends of SO₂, PM₁₀, NO₂ and CO annual air pollution characteristics in 1996–2008 and PM_2.5 for the period 2004–2008 for the following agglomerations: Prague, Brno and Moravian-Silesian Region and for the zone Ústí nad Labem Region.

Up to 1999 there was a significant decreasing trend in SO₂ and PM₁₀ concentrations in the agglomerations, the NO₂ concentrations decreased only slightly. In 2001 the decreasing trend was interrupted and, on the contrary, the SO₂ and NO₂ concentrations slightly increased; PM₁₀ concentrations increased significantly, mainly in the Ostrava agglomeration. In 2004, on the contrary, concentrations of all pollutants monitored in the agglomerations decreased, and SO₂ concentrations slightly increased in the Ústí nad Labem Region. Starting from 2005 all agglomerations recorded the increasing trend in NO₂, which was confirmed in 2006. As concerns PM₁₀ and PM_2.5, there has been a similar characteristic increasing trend since 2005, with the steepest progress in the Moravian-Silesian Region. In 2006, however, this trend continued only in PM₁₀ in the Prague and Brno agglomerations, in PM_2.5 in the Ústí nad Labem Region and in Brno. The increase of the pollutants� concentrations, and mainly of PM₁₀ (PM _2.5) in the years 2005 and 2006 is given mainly by deteriorated dispersion conditions. In 2006 these unfavourable meteorological conditions occurred on the whole territory of the Czech Republic. In the Ústí nad Labem Region and in the Moravian-Silesian Region, on the contrary, a very slight decrease of 24-hour PM₁₀ concentrations and stagnation of annual PM₁₀ concentrations were recorded. CO concentrations have remained at similar level since 1999. The highest average concentrations have been regularly measured in the Moravian-Silesian Region since 2000. In 2007 there was a marked decrease of air pollution caused by SO₂, PM₁₀, PM_2.5, NO₂ and CO in all agglomerations. The steepest decrease is apparent, after the previous increase, in hourly NO₂ concentrations in Brno. The decrease of pollutants� concentrations in the ambient air was influenced by more favourable meteorological and dispersion conditions in 2007. In 2008 the decrease of SO₂, PM₁₀ and NO₂ concentrations continued, but it was not as steep as in the previous year. PM_2.5 concentrations (measured in fewer localities than PM₁₀) and CO concentrations mostly stagnated; in Prague they slightly increased. The deepest decrease was recorded in the highest daily PM₁₀ concentrations. This could be caused by more favourable meteorological and dispersion conditions in April, November and December 2008 as compared with the previous year.

Fig. II.4.1.34 Trends of SO₂, PM₁₀, PM_2.5, NO₂ and CO annual characteristics in agglomerations, 1996-2008