groc2004 kap3 ang

	AIR POLLUTION IN THE CZECH REPUBLIC IN 2004 Czech Hydrometeorological Institute - Air Quality Protection Division

3. ATMOSPHERIC DEPOSITION IN THE CZECH REPUBLIC

Precipitation quality and atmospheric deposition have been monitored in the long term at relatively large number of stations in the Czech Republic. Precipitation quality stations operated by CHMI, ČGS, VÚV TGM, VÚLHM and HBÚ AV ČR from which data on precipitation quality and atmospheric deposition were processed in 2004, are plotted in Fig. 3.1. Information on individual stations and on types of sampling is listed in Table 3.4. In 1996, most of the CHMI stations switched over to weekly sampling intervals in line with the EMEP methodology. In 1997 the special weekly bulk sampling for heavy metals analysis was introduced at these stations.

Tables 3.5 and 3.6 contain average values of the chemical composition of atmospheric precipitation and the values of the 2004 annual wet deposition. Wet deposition charts were compiled for selected ions on the basis of all-round chemical analyses of precipitation samples, specifically for SO₄-S, NO₃-N, NH₄-N, H⁺ (pH), F^-, Cl^-, Pb²⁺, Cd²⁺ and 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 are preferred to bulk samples and weekly samples are preferred to monthly samples. Data from the stations operated by ČGS, VÚV and VÚLHM which are based on monthly bulk sampling (dustfall see Table 3.4) 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 gas 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 Table3.1.

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 (47 to 92 % of precipitation totals in 2004). Throughfall deposition generally includes wet vertical and horizontal deposition and dry deposition of particles and gases in forests; in case of sulphur, circulation of which within the forests is negligible, throughfall deposition is 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 at individual stations. The field of deposition flows 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 (Chapter 2.2). 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 in CHMI 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.

Results

The average value of total precipitation in the year 2004 for the territory of the Czech Republic reached 101 % of the long-term normal. As compared to the year 2003, which was markedly below normal (77 % of the long-term normal), the total precipitation thus increases the level of calculated wet deposition.
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. In 2004 there was recorded a slight increase of wet sulphur deposition as compared to the previous year (see Fig. 3.22). The increase was caused by higher total precipitation in 2004 because when we compare the sulphate concentrations in precipitation at individual stations there is a majority of stations with a slight decline of values as compared to those recorded in 2003. The highest values of wet sulphur deposition were reached in the Jizerské hory Mts. and the Českomoravská vrchovina Highlands.
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 2000–2004 it stagnated, 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 69,353 t for the Czech Republic�s territory for the year 2004 (see Table 3.2). After the previous decrease from the values markedly above 100,000 t, in the period 2000–2004 the sulphur deposition remained within the range from 70,000 to 75,000 t per year with the exception of the year 2003 which was markedly below normal as for the precipitation (see Fig. 3.21). Sulphur deposition reached the maximum values in the Krušné hory Mts., the Železné hory Mts. and the Krkonoše Mts.
The throughfall sulphur deposition field in several mountainous areas (the Krušné hory Mts., the Orlické hory Mts.) reaches higher values than the total deposition calculated as the sum of wet and dry deposition. The increased contribution can be attributed to horizontal deposition which is not included in total summary deposition because of uncertainties. Hoarfrost, icing and rime, and fog are normally highly concentrated and may significantly contribute to sulphur and other elements� deposition in mountainous areas. 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 3.3 shows the values of total and throughfall deposition for the forested areas of the Czech Republic since 1997. The higher values of throughfall deposition confirm its significance for the determination of total sulphur deposition.
The maps of both wet and dry nitrogen deposition are similar to those presented in the previous years. As compared with the year 2003 there was a slight decrease of wet deposition in the area of the Hrubý Jeseník Mts. (predominantly as a result of N/NH₄ decline) and, on the contrary, there was a slight increase in western and southern Bohemia. The most marked decline of dry deposition of the oxidized forms of nitrogen was recorded in 1998 (by about 20 % in comparison with the average for the years 1995–1997) and its decline continued up to 2002. A slight increase has been recorded in the past two years. The levels of wet deposition were more or less stable in the mentioned period (Fig. 3.22). In 2004 the total nitrogen deposition was 80,077 t of N (ox + red).year^-1 for the area of the Czech Republic (see Table 3.2), which is comparable with the values reached in the period 1999–2002 when the total depositon ranged between 77,000 and 85,000 t of N.year^-1 (the year 2003 was exceptional as it was significantly below normal as for precipitation as mentioned several times earlier). The highest values of total nitrogen deposition were reached in the Krušné hory Mts., Jizerské hory Mts. and the Orlické hory Mts.
The charts of both wet and dry deposition of hydrogen ions have shown relative minimal differences in the period of 2000–2004, nevertheless there was recorded a slight increase in 2004. It is shown in the map of total deposition of hydrogen ions (Fig. 3.13). 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 decrease of dry deposition of SO₂-S and NO_x-N.
After the year 2000 when the distribution of leaded petrol was finished the field of wet deposition of lead ions remains at a markedly lower level. The field of wet deposition for the year 2004 is similar as those in 2001–2003. A slight increase was recorded, similarly as in 2003 in the area of the Jizerské hory Mts. and the Krkonoše Mts., though not as much significant. Similarly as in the previous years, the highest values of wet deposition of cadmium ions were recorded also in this area.
The map of wet annual deposition of nickel ions for the year 2004 confirmed the decline of this deposition recorded in 2003.
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. 3.21) 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 , Pb) was also obvious. 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.