Heavy metals in the atmosphere represent a significant potential load for the remaining components of the environment. Within environmental protection �heavy metals� refer to a group of metals and metalloids with specific weight above 4 g.cm^-3. The Convention on Long Range Transboundary Air Pollution (CLRTAP) states the following elements: As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. It can be proved that these elements or their compounds are, already in trace concentrations, toxic for various parts of the environment. Heavy metals in the atmosphere are bound to suspended particulate matter.

The sources of anthropogenic heavy metal emissions are particularly processes of burning fossil fuels (As, Cd, Hg, Ni, Pb, Cr), iron production and processing (Fe, Mn, Cr, Ni, Cd), metallurgy of non- ferrous metals (As, Cd, Cu, Pb, Zn, Hg), incinerators (As, Cd, Cu, Pb, Zn, Hg), cement production (As, Cd, Pb, Hg, Ni), glass production (As, Cd, Pb, Hg, Zn), electrolytic production of chlorine and lye (Hg) and also use of leaded petrol (Pb). Generally, atmospheric heavy metal emissions are connected with high- temperature processes of formation of vapours of metals or volatile compounds of the above elements and their condensation and potential subsequent chemical transformation. This is mostly the case of metals with low melting and boiling temperatures and low vapour heat. Due to the processes of the entry to the atmosphere (condensation of oversaturated vapours, nucleation – formation of Aitken particles – and subsequent coagulation of the finest particles) heavy metals are similarly as e.g. polyaromatic hydrocarbons concentrated in fraction of fine particles of atmospheric aerosol, i. e. fractions with aerodynamic diameter below 2.5 μm (accumulation mode). The particles within the accumulation mode form the most stable aerodisperse system characterized by long residence times of the particles in the atmosphere and their transport over vast distances.

Heavy metals contents in SPM have been monitored in the Czech Republic at a relatively large number of stations (total 108 stations in 2000). In addition to the data from CHMI�s own stations (23 in 2000), data obtained from ORGREZ stations (10 stations in 2000), including that archived since 1986, has been stored in the ISKO air pollution database since 1996 on a regular basis. The systematic provision of data on heavy metals observed in the atmosphere – including information on the respective stations and measuring methods – to the ISKO nation-wide ambient air pollution database, has been largely extended by the numerous stations of the Public Health Service network since 1997 (75 stations in 2000).

SPM sampling methods, and the analytical procedures of measuring heavy metal contents in SPM are based on analogous methodologies. In CHMI, the concentration of metals in the air was analysed mainly by the atomic absorption spectrometry (AAS) till 1996 using membrane filters for (usually weekly) sampling followed by mineralization using hot nitric acid. This method is still used at the stations of the Public Health Service and ORGREZ. Since 1998 the CHMI has used the AAS method only for determination of cadmium concentration in the atmosphere at selected stations. At several Public Health Service stations the polarographic method and inductively coupled plasma – atomic emission spectrometry (ICP-AES) are also used for the analysis of heavy metals after mineralization of SPM samples. Since 1997 the CHMI stations have determined the concentration of heavy metals in the air also by a non- destructive analyses of X-ray fluorescence (XRF) using teflon filters. Within the framework of the Black Triangle programme the inductively coupled plasma – mass spectrometry (ICP-MS) is applied, with high-volume sampling on glass-fibre filters.

Table 2-77 gives annual arithmetic means of arsenic, cadmium, lead and nickel concentrations for the respective selected organisation�s stations. In addition to lead and cadmium for which the ambient air pollution limits are set in Federal Committee for the Environment�s Decree attached to Act No. 309/1991 (see Table 2-1), arsenic, nickel (and also mercury) are included in the list of other pollutants which are necessary to be considered during ambient air quality assessment and management pursuant to the Directive 96/62/EC and for which the respective Daughter Directive setting the respective air pollution limit values of these elements is being prepared.

It is evident from Table 2-77 that in 2000 the limit value for cadmium was not exceeded at any station. At the Tanvald station (HS), where the limit value for cadmium was markedly exceeded in the past, the measurements discontinued at the end of 1999. The value of annual average cadmium concentration at Souš station (CHMI) has the level above one half of the limit value. The highest annual average lead concentrations were measured at Český Těšín (HS) and Bohumín-Čáslavská (HS) – 103.5 ng.m^-3 and 100.5 ng.m^-3 respectively. At the Příbram station (HS), where the long-term highest lead concentration fluctuated above on half of the limit value, the average concentration was 43.6 ng.m^-3 in 2000. The highest annual average arsenic concentration (9.4 ng.m^-3) was measured at Ostrava-Novinářská station.

The graphs in Figs. 2-73, 2-74 and 2-75 illustrate the development of annual arsenic, cadmium and lead concentrations in the atmosphere between 1988 and 2000 at selected CHMI, ORGREZ, and the Public Health Service stations for which archived data for this period are available. The 2000 figures confirm the already indicated drop in heavy metals concentrations at most stations. Therefore many stations, especially those operated by ORGREZ, have discontinued the measurements. At the Souš station (CHMI) the cadmium concentration was high even in 2000 (above one half of the current limit value). The HS stations in Liberec and Tanvald, where cadmium and arsenic limit values were exceeded significantly in long terms, have discontinued the measurements. The annual limit value for cadmium was also exceeded at the Dubí and Ústí nad Labem stations in the past.

The well-apparent recent reduction in these metals� levels in the air over the past few years is attributable not only to declining SPM concentrations in that period but also to an obvious drop of these metals� contents in SPM [4] after 1990. This decline reflects the decrease in fossil fuels consumption and, consequently, decrease in particulate emissions, especially from large air pollution sources. Significant decrease of the above metals� air pollution levels (similarly as in sulphur oxide and SPM), particularly after 1997, suggests the expected development connected with the date of entry into force of the emission limit values for air pollution sources.

The maps in Figs. 2-76 and 2-77 illustrate estimated regional distribution of the fields of annual cadmium and lead concentrations in the atmosphere, generated by means of map algebra based on the fields of these metals� percentages in SPM and the field of annual arithmetic means of SPM concentrations (Fig. 2-44). The country-wide estimate of the distribution of heavy metals concentrations is based primarily on the assumption that it is viable to apply the measured percentages – based on estimates of the regional distribution of the given element�s percentage in SPM – to those SPM concentration measurements in which the metal in SPM is not determined. The fields of lead and cadmium fractions in SPM were drawn on the basis of the fractions measured at 108 stations of the stated organisations, and on the basis of estimates of these metals� fractions in SPM for areas with inadequate monitoring of metals while relying on their similarities with areas in which metal fractions in SPM have been measured. The distribution of annual cadmium, lead, arsenic and nickel fractions in SPM at CHMI, ORGREZ and the Public Health Service stations is listed in Table 2-78.

The field of cadmium and lead concentrations in the atmosphere serves as the basis for compiling fields of deposition flows of these metals using the dry atmospheric deposition methodology (Chapter 3).

Tab. 2-77 Concentrations of arsenic, cadmium, lead and nickel in SPM at selected stations, 2000

Tab. 2-78 Annual cadmium, lead, arsenic and nickel fraction distribution in SPM, 2000