Figs. 2-52, 2-53, 2-54 contain map diagrams¹ [8] illustrating profiles of principal ambient air pollution characteristics (annual arithmetic means and 95th percentiles) of basic pollutants (SO₂, SPM and NO_x) sorted in districts, showing the amount by which the relevant ambient air pollution limits were exceeded. These characteristics represent estimates of values averaged over a district within the 1990–2000 period, calculated according to the methodology based on the year 1996. It is to be noted at this point, however, that this regionalised assessment of principal ambient air pollution characteristics� courses for the principal pollutants in the Czech Republic is based on different numbers of accessible measuring stations in individual districts.

Fig. 2-52 illustrating the course of sulphur dioxide air pollution characteristics in 1990–2000 shows a marked downward trend in SO₂ pollution in all districts of the Czech Republic. The steepest decrease was recorded in north Bohemia and in the Capital City of Prague where the highest levels were recorded in early 90s. The most marked decrease of SO₂ concentrations was recorded in 1994 throughout the whole territory of the Czech Republic. In the period between 1994 and 2000 the regionalized means of SO₂ air pollution characteristics did not exceed the set limit values in any district of the Czech Republic. In 1998–2000 further gradual decrease of SO₂ pollution occurred and in this period no exceedences of the current limit value were recorded at any measuring station.

The suspended particulate matter (SPM)² air pollution development (Fig. 2-53) shows similar falling trend in the Czech Republic within 1990–2000 period as in SO₂ pollution, less marked in the early 90s, mainly in Ostrava Region. In this region this type of air pollution stagnated until 1996. In 1997–2000 a marked downward trend was recorded throughout the whole territory of the Czech Republic, including the Ostrava Region. This downward trend, however, was confirmed only in several, mainly rural districts in 2000, in the districts with the prevailing share of residential areas this type of air pollution rather stagnated. A slight increase was recorded in large cities (in 95th percentiles). Since 1998 the regionalized means of SPM air pollution characteristics have not exceeded the current limit values in any district.

The recent falling trend of SO₂ and SPM concentrations results from the concurrence of several factors: efficient direct environmental measures applied to sources of air pollution and changes in favour of gas heating, which resulted in decline in SO₂ and solid particle total emissions, and more favourable meteorological and dispersion conditions, mainly in winter months. In the end of 2000, however, these conditions were less favourable than in 1999 (see Chapter 2.4).

In respect to nitrogen oxides, a slightly increasing trend of air pollution was observed until 1997 (see Fig. 2-54). This was caused mainly by increasing share of road transport. The increase of NO_x concentrations in the districts of south Moravia was recorded in 1995 with the installation of new urban stations by district or municipal authorities. In the same year one Public Health Service station in Děčín was moved to a more exposed site. In 1998 and 1999 this trend was broken and on the contrary a slight decrease of NO_x concentrations was recorded due to lower emission from stationary sources in winter months of 1998, and especially in the Moravian districts, probably due to the fact that some sources were shut down and to the setback in production in 1999. In 2000 this slightly decreasing trend was confirmed only in several districts (e.g. Děčín District), in most cases stagnation of this type of pollution prevailed. A slight increase of air pollution caused by NO_x was recorded in large cities: Prague, Plzeň and Ostrava. (In the Šumperk District the steep decline of NO_x concentrations was influenced by the closing of two OÚ Šumperk stations).

Fig. 2-56 illustrates the development of annual air pollution characteristics of basic pollutants monitored in the long term (1982–2000) for the Northwest, Prague and Ostrava Regions. Generally, beginning from the year 1988 a downward trend can be observed, both in SO₂ and SPM, in air pollution of the Czech Republic and this decrease is markedly significant after 1996. After 1996 the decrease in NO_x pollution is apparent in the Northwest Region and the Ostrava Region as well. In the Northwest Region the 2000 levels of air pollution characteristics of SO₂, SPM and NO_x were the lowest ones within the whole period.

Fig. 2-57 presents the long-term development of air pollution and the course of temperature in winter seasons. When comparing the course of temperature of two comparable winter half years 2000/2001 and 1989/1990 a marked decrease in SO₂ and SPM air pollution is evident in Prague, in the northwest Bohemia and in the Ostrava Region. As regards NO_x the comparison of the above two winter half years shows a slight decrease of NO_x values in the northwest Bohemia and in the Ostrava region. In Prague, on the contrary, the comparison of the 2000/2001 and 1989/1990 winter half years shows a slight increase of air pollution caused by NO_x. Beginning from the 1992/1993 to 2000/20001 winter period the situation in Prague generally stagnated as concerns air pollution caused by NO_x.

Notes
¹ The method based on map diagrams is one of the methods of cartographic presentation using spot diagrams which represent both the quality and the quantity of the given phenomenon (absolute or relative values). The map diagrams depict summary values for a given territory in the centre of which they are located, i.e. not for individual spots. The Yearbook uses this method for depicting the developments over time and showing the volume of air pollution characteristics of principal pollutants in individual districts of the Czech Republic.
² Long-term series of dust pollution are characterised by SPM concentrations regardless the SPM matter size. All automated CHMI stations have been measuring the PM₁₀ fraction since 1996. When using these measurements to estimate regional SPM means, a conversion coefficient 1.2 was applied.

Tab. 2-64 Highest daily pollutant concentrations at stations in the Czech Republic in 2000

Tab. 2-65 Stations with highest annual arithmetic means of pollutant concentrations, the Czech Republic 2000

Tab. 2-66 Stations with highest relative (absolute) frequency of IH_d exceedence, the Czech Republic 2000

Tab. 2-67 Stations with highest values of 95th (90th) percentiles of daily pollutant concentrations, the Czech Republic 2000

Tab. 2-68 Stations with highest relative frequency of short-term exceedence of IH_k, the Czech Republic 2000

Tab. 2-69 Stations with highest values of 95th percentiles of half-hour pollutant concentrations, the Czech Republic 2000

Tab. 2-70 Highest half-hour (3-hour) pollutant concentrations at stations, the Czech Republic 2000