Chemical composition (precipitation quality) and atmospheric deposition have been monitored in the long term at relatively large number of stations in the Czech Republic. In 2006 the ISKO database, which is the basis of the following assessment, obtained data on precipitation quality from 58 localities in total (17 ČGS, 15 CHMI, 14 VÚLHM, 6 VÚV TGM and 6 HBÚ AV ČR, see Fig. III.1). Most of the CHMI stations measure wet-only samples in weekly interval (monthly interval was switched over to weekly interval in 1996 in line with the EMEP methodology). In 1997 the special weekly precipitation sampling, �bulk� type, (with non-specified contains of dustfall) for heavy metals analysis was introduced at these stations. In the localities of other organizations monthly sampling (or irregular sampling) is used for measuring concentrations in precipitation (�bulk�type) in the open area (or throughfall). The detailed information on individual localities and sampling types is presented in Table III.4.

Tables III.5 and III.6 contain average values of the chemical composition of atmospheric precipitation and the values of the 2006 annual wet deposition.

Wet deposition charts were compiled for selected ions on the basis of all-round chemical analyses of precipitation samples, specifically forSO₄^2-- S, NO₃^-- N, NH₄⁺ - N, H⁺ (pH), F , Cl^-, Pb²⁺, Cd²⁺  a Ni²⁺.
The above ions were selected to represent deposition fields with regard to their considerable impact on the various spheres of the environment. Wet deposition charts for each of the ions were derived from the field of ion concentrations in precipitation (based on annual mean concentrations weighted by precipitation totals calculated from the data observed), and from the field of annual precipitation totals which was generated on data from 750 precipitation gauging stations, taking into account the altitude�s effect on precipitation amount. When constructing wet deposition fields, results of wet-only samples analysis are preferred to �bulk� samples with dustfall, and weekly samples are preferred to monthly samples. Data from the network stations operated by ČGS, VÚV TGM and VÚLHM based on monthly �bulk� sampling with dustfall (see Table III.4) are modified by empirical coefficients expressing the individual ions� ratios in �bulk� and �wet-only� samples (values for each of the ions from 0.94 to 1.35) for the purpose of the development of the wet deposition charts.

In addition to wet deposition, also dry and total deposition charts are included for sulphur, nitrogen and hydrogen ions. Dry sulphur and nitrogen deposition was calculated using fields of annual mean SO₂ and NO_x concentrations for the Czech Republic, and the deposition rates found in [21] for SO₂ 0.7 cm.s^-1/0.35 cm.s^-1, and NO_x 0.4 cm.s^-1 / 0.1 cm.s^-1, in case of forested/unforested area. Total deposition charts were produced by adding S and N wet and dry deposition charts. The wet hydrogen ion deposition chart was compiled on the base of pH values measured in precipitation. Dry hydrogen ion deposition reflects SO₂ and NO_x deposition based on stechiometry, assuming their acid reaction in the environment. The total hydrogen ion deposition chart was developed by summation of wet and dry deposition charts.
The average deposition fluxes of S, N and H are presented in the following table:

Tab. III.1 Average deposition fluxes of S, N and H in the Czech Republic, 2006

Throughfall sulphur deposition chart was generated for forested areas from the field of sulphur concentrations in throughfall and a verified field of precipitation, which was modified by a percentage of precipitation amounts measured under canopy at each station (49–98 % of precipitation totals in 2006). Throughfall deposition generally includes wet vertical and horizontal deposition and dry deposition of particles and gases in forests; in case of sulphur, its circulation within the forests is negligible; throughfall deposition is thus considered to provide a good estimate of total deposition.

Heavy metal wet deposition charts for Pb, Cd and Ni were derived from concentrations of these metals in �bulk� precipitation samples with dustfall at individual stations. The fields of dry deposition of Pb and Cd contained in SPM (dry Pb and Cd deposition) were derived from the fields of these metals� concentrations in the ambient air (see Chapter II.4.2). The deposition rate of Cd contained in SPM was taken as 0.27 cm.s^-1 for a forest and 0.1 cm.s^-1 for unforested terrain; the figures for Pb are 0.25 cm.s^-1 for a forest and 0.08 cm.s^-1 for unforested terrain [21].

The data on precipitation quality are controlled routinely using the method of ion balance calculation (the difference between the sum of cations and the sum of anions in the sample should meet the allowable criteria which differ slightly in various organizations).
Another control is carried out by comparing the calculated conductivity and the measured conductivity which both should meet the allowable criteria.

Analysis of the blank laboratory samples is also used and blank field samples are monitored and assessed continuously. This enables the control of work during sampling and the control of changes occurring due to transport, manipulation, storage and preparation of the samples prior to the chemical analysis.

•  The precipitation in the year 2006 for the territory of the Czech Republic was slightly above the the long-term normal; it amounted to 708 mm in the average, which represents 105 % of the long-term normal (for the years 1961–1990).
• Wet sulphur deposition decreased after 1997 below 50,000 t and this trend continued up to 1999. Since 2000 the profound decrease had not continued and the values remained more or less at the level of 1999 with the exception of lower depositions in 2003, where the precipitation total was markedly subnormal. The highest values of sulphur wet deposition were recorded in the Ústí nad Labem Region (locality Doksany) and in the Jizerské hory Mts. and in part of the Moravskoslezské Beskydy Mts.
• Dry sulphur deposition the most significant decline of which was recorded in the year 1998 (the value decreased by 45 % in comparison with the average value for the period 1995–1997), continued to decline in 1999–2000. In 2000–2006 the deposition field remained at the same level, which is coherent with SO2 concentrations in the ground-level ambient air. The field of total sulphur deposition is the sum of wet and dry depositions and it shows the total sulphur deposition amounting to 65,556 t for the Czech Republic's territory for the year 2006 (see Table III.2). After the previous decrease from the values markedly above 100,000 t, in the period 2000–2006 the sulphur deposition remains within the range from 65,000 to 75,000 t per year with the exception of the year 2003 which was markedly below normal as for the precipitation (see Fig. III.21). The total sulphur deposition reached the maximum values in the Krušné hory Mts.,the Jizerské hory Mts. and in the environs of the city of Ostrava.
• The throughfall sulphur deposition field reached the maximum values in the Krušné hory Mts., in the Jizerské hory Mts. and in the Orlické hory Mts. In some parts of the mountains the values of throughfall deposition reach, in the long-term, higher values than the values of the total sulphur deposition determined as the sum of wet (only vertical) and dry deposition. The increased contribution can be attributed to deposition from fog and low clouds which is not included in total summary deposition because of uncertainties. Hoarfrost and fog are normally highly concentrated and may significantly contribute to sulphur and other elements� deposition in mountainous areas and areas with frequent fogs (valley fogs, fogs near water courses and lakes). The problem is in a very erratic character of this type of deposition from place to place where some uncertainties may occur when extrapolating to a wider area. In such case, the field of throughfall deposition can be considered as illustrative for what values the total sulphur deposition (including horizontal deposition) might reach, because sulphur circulation within vegetation is, unlike other pollutants, negligible. Table III.3 shows the values of total and throughfall deposition for the forested areas of the Czech Republic since 1997. The higher values of throughfall deposition in all given years, i.e. 1997–2006, (containing also fog and low clouds deposition) confirm its significance for the determination of total sulphur deposition.
• The map of wet deposition of nitrates shows higher values in the territory of the Ústí nad Labem Region (Krušné hory Mts., the environs of the locality Doksany), in the Lužické hory Mts., in the Jizerské hory Mts. ,in the Krkonoše Mts.,in the Orlické hory Mts., Hrubý Jeseník Mts. and in the part of the Moravskoslezské Beskydy Mts. The highest values of wet deposition of ammonia ions were recorded, similarly as in 2005, in the Jizerské hory Mts. and in the Krkonoše Mts. and newly also in the territory of the Ústí nad Labem Region (in the environs of the locality Doksany) and in the part of the Moravskoslezské Beskydy Mts. The total wet deposition of the oxidized forms of nitrogen in the territory of the Czech Republic remains, as compared to the previous year, at the same level (see Fig. III.21). The map of dry nitrogen deposition is of similar character as in the previous years. Dry deposition of oxidized forms of nitrogen was declining up to the year 2002 (when the value reached 48 % of the value of the average for the years 1995–1997). The trend of slight increase in the years 2003–2004 was not confirmed, in 2005 a slight decline occurred, followed again by a slight increase in 2006 (see Fig. III.21).
• In 2006 the total nitrogen deposition reached 80,561 t of N (ox+red). year^-1 for the area of the Czech Republic (see Table III.2), which is comparable with the values reached in the period 1999–2005 when the total deposition ranged between 77,000 and 85,000 t of N. year^-1 (with the exception of the year 2003 which was significantly below precipitation normal). The highest values of total nitrogen deposition were reached, similarly as in the previous year, in the Jizerské hory Mts., Krkonoše Mts. and Orlické hory Mts., a slight increase was recorded in the area of the Krušné hory Mts. and in the most of the remaining part of the Ústí nad Labem Region.
• The charts of both wet and dry deposition of hydrogen ions have shown relative minimal differences in the period of 2000–2006. The maximum values of wet deposition were reached in the Jizerské hory Mts. and the Krkonoše Mts. The map of total deposition of hydrogen ions is similar as in the previous year (Fig. III.13). In the second half of the 90�s of the last century both wet and dry depositions of hydrogen ions decreased by 50 % per the whole area of the Czech Republic, the decrease of dry deposition of hydrogen ions values was in coherence with the already mentioned decrease of dry deposition of SO₂–S and NO_x–N.
• After the year 2000 when the distribution of leaded petrol was finished the values of wet deposition of lead ions markedly decreased. The field of wet deposition for the year 2006 is in the majority of the territory of the Czech Republic similar as in the previous years, with the exception of the areas of the Jizerské hory Mts., Orlické hory Mts. and Ždárské vrchy Mts., where a slight increase was recorded. The map of dry lead deposition is similar as in the previous years.
• Similarly as in the previous years the highest values of dry and wet deposition of cadmium ions were recorded in the area of the Jizerské hory Mts. This is probably local pollution as this is the area with long-term increased cadmium concentrations in the ambient air. Significant emission source from the glassworks is one of the probable reasons of this situation. The values of wet deposition, however, did not exceed 0.5 mg.m^-2.year^-1.in 2006.
• The map of wet annual deposition of nickel ions shows again the increase of precipitation pollution in comparison with the previous years. The significant increase was recorded in the Jizerské hory Mts., and Krkonoše Mts., where in some parts the deposition increased above 4 mg.m^-2.year^-1.
• In 2006 the increase of wet deposition of fluoride ions, recorded in 2005 in the locality Lužnice, was not confirmed in 2006. The highest values were recorded in the Jizerské hory Mts. and in the Krkonoše Mts.
• After the decrease of wet deposition of several components (mainly sulphates, hydrogen ions and lead ions) in the second half of the 90�s, the development of annual wet deposition of the main elements as measured at selected stations in the Czech Republic (Fig. III.22) shows stagnation instead. The decrease of sulphate deposition was substantial not only at the exposed stations as Ústí nad Labem, Prague-Libuš or Hradec Králové but it was also obvious at the background stations Košetice and Svratouch. The decrease was substantial at the station Ústí nad Labem where the wet sulphate deposition decreased by 60 % after 1995 and where the decrease of other substances (NO₃^-, NH₄⁺, Pb²⁺) was also obvious. During the period 2003–2005 this locality recorded a slight increase (NO₃^-, SO₄^2-, Pb²⁺), which was not apparent in 2006. With the development of sulphur and nitrogen deposition the development of the proportion of both elements can be observed in atmospheric precipitation. Since the second half of the 90�s a slight increase of nitrogen and sulphur proportion has been observed.

Tab. III.1 Average deposition fluxes of S, N and H in the Czech Republic, 2006

Tab. III.2 Estimate of the total annual deposition of the given elements in the Czech Republic (78,841 sq. km) in tonnes, 2006

Tab. III.3 Estimate of the total annual deposition of sulphur on the forested part of the Czech Republic (16,990 sq. km) in tonnes, 1997–2006

Tab. III.4 Station networks monitoring atmospheric precipitation quality and atmospheric deposition, 2006

Tab. III.5 Average annual concentrations of principal pollutants in atmospheric precipitation at stations in the Czech Republic, 2006

Tab. III.6 Annual wet atmospheric deposition at stations in the Czech Republic, 2006

Fig. III.1 Station networks monitoring atmospheric precipitation quality and atmospheric deposition, 2006

Fig. III.2 Fields of annual wet deposition of sulphur (SO₄^2- - S), 2006

Fig. III.3 Fields of annual dry deposition of sulphur (SO₂ - S), 2006

Fig. III.4 Fields of annual total deposition of sulphur, 2006

Fig. III.5 Fields of annual throughfall deposition of sulphur, 2006

Fig. III.6 Fields of annual wet deposition of nitrogen (NO₃^- - N), 2006

Fig. III.7 Fields of annual wet deposition of nitrogen (NH₄⁺ - N), 2006

Fig. III.8 Fields of annual total wet deposition of nitrogen, 2006

Fig. III.9 Fields of annual dry deposition of nitrogen (NO_x - N), 2006

Fig. III.10 Fields of annual total deposition of nitrogen, 2006

Fig. III.11 Fields of annual wet deposition of hydrogen ions, 2006

Fig. III.12 Fields of annual dry deposition of hydrogen ions corresponding to SO₂ and NO_x deposition, 2006

Fig. III.13 Fields of annual total deposition of hydrogen ions, 2006

Fig. III.14 Fields of annual wet deposition of fluoride ions, 2006

Fig. III.15 Fields of annual wet deposition of chloride ions, 2006

Fig. III.16 Fields of annual wet deposition of lead ions, 2006

Fig. III.17 Fields of annual dry deposition of lead, 2006

Fig. III.18 Fields of annual wet deposition of cadmium ions, 2006

Fig. III.19 Fields of annual dry deposition of cadmium, 2006

Fig. III.20 Fields of annual wet deposition of nickel ions, 2006

Fig. III.21 Annual deposition of sulphur (SO₄²–S, SO₂–S) and oxidated forms of nitrogen (NO₃^-–N, NO_x–N) and hydrogen in the Czech Republic, 1995–2006

Fig. III.22 Annual wet deposition at selected stations between 1991 and 2006, the Czech Republic