A review of air pollution and atmospheric deposition dynamics in southern Saxony, Germany, Central Europe

AE International – Europe Atmospheric Environment 37 (2003) 671–691

A review of air pollution and atmospheric deposition dynamics in southern Saxony, Germany, Central Europe . Matschullata, Frank Zimmermanna,*, Herbert Luxb, Willy Maenhautc, Jorg Kirsten Plessowa, Friedrich Reuterb, Otto Wienhausb a

Interdisciplinary Environmental Research Centre, Freiberg University of Mining and Technology, Brennhausgasse 14, D-09599 Freiberg, Germany b Institut fur . Pflanzenchemie und Holzchemie, Technische Universitat . Dresden, Pienner Strae 21, D–01 735 Tharandt, Germany c Instituut voor Nucleaire Wetenschapen, Universiteit Gent, Proeftuinstraat 86, B–9000 Gent, Belgium Received 29 May 2002; received in revised form 23 September 2002; accepted 4 October 2002

Abstract This is the first comprehensive compilation of air pollution history in the Erzgebirge region. It presents selected data sets from more than 20 years of continuous research, chosen after rigorous quality control. Gases and particulates, and wet deposition are discussed in sequence. The gases include SO2, NOx, O3, and fluorine compounds. SO2-concentrations declined from about 80 to 120 mg m3 until 1990 to 5–10 mg SO2 m3 air today, while NOx shows little change, and O3 steadily increases as of 1990. Fluoride deposition decreased with SO2. Particle deposition is differentiated by sampling methods and grain sizes, and their chemical composition. The total amount of aerosols has decreased in the past 12 years, and many trace constituents now show 10% of their previous concentrations. Precipitation is represented by wet only, throughfall, fog and cloud water deposition, including major and minor chemical compounds. As with the gases, S-compounds decreased considerably. While NO3-N-concentrations show a slight decline (from 13 to 10–11 kg ha 1 a 1 in throughfall deposition); no trend is visible for NH4-N. As of the mid-1990s, continuously lower base cation inputs are being measured, and pH-values are on steady increase (now 4.8). The final synopsis rounds up the experience gained from those valuable data sets and can be used for many regions worldwide. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Aerosol; Dry deposition; Bulk deposition; Atmospheric deposition trends; Time series; SO2 NOx; O3; Erzgebirge; Black triangle

1. Introduction and regional air pollution history Southern Saxony presents a highly diverse landscape bordering the Czech Republic. The region features undulating hills and mountains, with altitudes from a little over 150 m a.s.l. at the Elbe river valley to more than 1000 m at the Erzgebirge crest. Extensive forests, agricultural land, and industries, often still related to the great mining history of the area, make for a unique *Corresponding author. E-mail addresses: [email protected] (F. Zimmermann), [email protected] (J. Matschullat).

checkerboard of diverse land-use patterns. Until recently, southern Saxony was part of a larger region including SW Poland (Silesia) and Northern Czech Republic (Northern Bohemia), with the ugly nickname ‘‘Black Triangle’’. Fortunately, the last few years have seen major improvements in air quality status and although considerable work is still needed, people can now refer to the region as a green triangle—acknowledging the density of forests and rich semi-natural landscapes. One of the first local references on air pollutionrelated environmental damage dates back to the late 17th century (Lehmann, 1699). In his chronicle ‘‘Historical scene of the peculiarities in the Meissen upper

1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 2 ) 0 0 8 2 9 - 4

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Erzgebirge’’, Lehmann described the environmental impact of the Annaberg silver smelters. Many more local examples exist and even back to Agricola (1557), old depictions are available that demonstrate the abundance and impact of late medieval ore dressing and smelting facilities in the area. Later, a rapid industrialisation led to rising emissions in the mid-19th century. In those days, even more intense environmental damage occurred. The newly established industrial enterprises were almost exclusively built in river valleys because of their high water demand. Thus, a whole chain of dispersed industrial centres emerged causing atmospheric pollution. Other emission centres grew in the hard coal mining districts of Zwickau and Lugau. Olsnitz as well as in the area around Chemnitz (Fig. 1). The predominant spruce forest, itself a heritage from earlier mining and smelting history, became most seriously impaired by the industrial emissions. Environmental damage could no longer be neglected and led to the establishment of a special branch of forestry research . in the mid-19th century. A first survey by Schroter (1907), entitled ‘‘The smoke-emitting sources in the kingdom of Saxony and their influence on forestry’’ is one witness for this period. This type of air pollution, characterised by local pollution sources, primarily situated in the valleys, persisted almost unchanged over centuries (16th–19th century), characteristic for the northern slope of the

Erzgebirge. Regional air pollution occurred only at the transition from the northern slope to the hilly Erzgebirge foreland in Saxony. There, zones of larger pollution dispersal were found juxtaposed or even partly superimposed. This gave rise to discussions among forestry professionals, especially concerning the question whether there was a connection between the hoarfrost breakage calamities in the Erzgebirge and the increasing number of condensation cores in the air due to industrial waste gases from the NW. Bohemian basin (Dobele, 1935; Heger, 1935, 1940; Lampadius, 1941; Singer, 1916). ‘‘Modern’’ air pollution became apparent after the second World War with the installation of numerous coal power plants and related industries both in the Bohemian basin and in Saxony. In the 1950s, the relation between increasing spruce decline phenomena and air pollution became more and more apparent (Materna, 1956, 1962; Pelz, 1962). Even though the Erzgebirge shares many meteorological and climatic characteristics with other Central European mountainous areas, the dispersion of emissions in southern Saxony depends on local meteorological particularities. In contrast to the northern slope, extensive air pollution caused by specific local climatic conditions occurred along the southern slope of the Erzgebirge and its ridges (Flemming, 1964). Wind and turbulence are the dominant meteorological factors in

Leipzig

Dresden

Silesia Zittau Mountain

Chemnitz

Eastern Erzgebirge Elbe Sandstone Mountains

Central Erzgebirge

Western Erzgebirge

Northern Bohemia

Fig. 1. Geographical position of the monitoring stations in the Erzgebirge (parts of Europe as an inset with Saxony in white).

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air pollution transfer. Comparatively stable air stratification occurs under SE winds—this leads to a focussed concentration of pollutants at a scale-height above 500 m a.s.l. This stratification is reduced immediately across the southern Erzgebirge escarpment due to dynamic and thermal influences that allow for a largescale dispersal of industrial waste gases and dusts from the NW-Bohemian basin. Temperature inversion is another common phenomenon. The inversion layer is lowest in winter and may be stable over several days. This leads to intense smog phenomena in the Bohemian basin. At the same time, the higher reaches of the Erzgebirge are almost free of pollutants and display a very high air quality. Sometimes, this ‘‘Bohemian fog’’ crosses the Erzgebirge ridge and it flows down the Saxonian Erzgebirge, resulting in SO2-deposition peaks. Thermal destabilisation of the atmospheric layers often occurs on ridges and passes that then serve as pollutant pathways in northerly direction. This destabilisation occurs more often in summer. In spring and fall, the two effects mix and thermal effects prevail in the mornings of radiation-rich days. Local differences are more pronounced in winter as compared to summer conditions (Zimmermann et al., 1997).

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1.1. Monitoring networks 1.1.1. Atmospheric gases The extensive spruce decline phenomena in the areas around Deutscheinsiedel and Markersbach (boundary between the Elbe Sandstone Mountains and the eastern Erzgebirge) initiated the establishment of a gas monitoring network in the mid-1960s, using SO2-aspirators (TCM method, modified after Herrmann, 1965). This network was a joint effort by the Institute of Phytochemistry and Wood Chemistry (Dresden University of Technology, TUD), the Bezirkshygieneinspektionen Chemnitz and Dresden (BHI), and the Meteorological Service of the former GDR (MD). In the 1970s, SO2concentration records (half-hour values) were started by MD and BHI, using the coulometric instruments CM 4 and CM 5 (Junkalor, Dessau). After German re-unification, a more comprehensive air pollution monitoring network was build-up in Saxony (Table 1; Fig. 1), organised under the auspices of the Regional Office for Environment and Geology (LfUG). Today, forest ecosystem monitoring stations exist at Carlsfeld and Fichtelberg in the western Erzgebirge, eastern Erzgebirge at Schwartenberg

Table 1 Atmospheric gas and deposition monitoring stations in the Erzgebirge. Elevations in m above sea level Station

Owner

Elevation Site characteristics

Components

Start yr End yr

Altenberg Annaberg Aue Bad Schandau B.arenstein Carlsfeld

SLAF LfUG LfUG SLAF LfUG LfUG

750 m 545 m 348 m 260 m 705 m 896 m

Spruce forest Urban, traffic Urban, traffic Beech forest, remote Urban Forest, remote

Cunnersdorf Fichtelberg Klingenthal Lehnmuhle .

SLAF LfUG SLAF UBA

440 m 1214 m 840 m 525 m

Spruce forest Mountain, remote Spruce forest Forest, remote

Luckendorf . Marienberg Mittelndorf

UBA LfUG LfUG

490 m

Forest, remote Urban, background Rural

Bulk, throughfall SO2, NOx, O3 SO2, NOx, O3 Bulk, throughfall SO2 SO2, O3 Wet only, dust Bulk, throughfall SO2, O3 Bulk, throughfall SO2, NOx, O3 Wet only SO2, NOx, O3 Wet only SO2, NOx, O3 Wet only, dust SO2, NOx, O3 Wet only, bulk, throughfall, fog, dust, aerosols SO2, NOx, O3 Bulk, throughfall SO2, NOx, O3 SO2, NOx, O3 Wet only, bulk, throughfall, dust, aerosols SO2, NOx, O3 Wet only, dust

2000 1988 1989 1998 1981 1991 1991 1993 1970 1993 1993 1993 1992 1985 1995 1995 1992 1984 1991 1994 1998 1993 1985 1971 1985

Oberb.arenburg TUD TUD, TUBAF Olbernhau LfUG SLAF Schwartenberg LfUG Tharandt forest TUD TUD, TUBAF Zinnwald LfUG

323 m 735 m 448 m 720 m 787 m 385 m 877 m

Forest, remote Spruce forest Urban, background Spruce forest Mountain, remote Forest, remote Forest, remote Mountain, remote

2001

1999 2000

LfUG: Regional Office for Environment and Geology; SLAF: Saxonian Regional Office for Forestry; TUBAF: Freiberg University of Mining and Technology; TUD: Technical University of Dresden; UBA: German Environmental Protection Agency.

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(Central Erzgebirge), and at Zinnwald. The central Erzgebirge lacks a representative monitoring station. The station at B.arenstein continued to operate until late 2001, although with a slightly different programme. In addition, data from Olbernhau and Annaberg are available (monitoring within the town boundaries). This governmental network is supplemented by the station at Oberb.arenburg (OBB), eastern Erzgebirge, initiated by TUD and today jointly operated with the Interdisciplinary Environmental Research Centre of Freiberg University of Mining and Technology (TUBAF). It was based on measuring equipment (Horiba APSA 350E, Horiba APOA 350E, Ecophysics CLD 700), comparable with the governmental network. The Lehnmuhle . station, operated by the Environmental Protection Agency (UBA), complements this arrangement. Other stations, monitoring forested areas in southern Saxony are Mittelndorf (LfUG) in the ‘‘Elbe sandstone mountains’’; Luckendorf . (UBA) in the Zittau Mountains; and Tharandt Forest (TUD); see Table 1 and Fig. 1. 1.1.2. Atmospheric deposition The relevance of atmospheric deposition for understanding potential air pollution effects led to the parallel establishment of a related monitoring network. In the 1970s and early 1980s, element inputs were measured at single sites, and only at irregular intervals in the Erzgebirge. Noteworthy are the works of Pankert and Panning (1975), and unpublished data in the Eastern Erzgebirge and by Flemming and Geiler (1985) in Neunzehnhain in the central Erzgebirge. In the early 1980s, ‘‘forest decline’’ and ‘‘acid precipitation’’ led to the design of monitoring stations for atmospheric deposition at many places in Europe, including the former GDR. This included the network of the Meteorological Service (1973) and monitoring stations of the Forestry College in Eberswalde (lowlands) and the Institute of Phytochemistry in Tharandt (highlands). The MD monitoring network started in 1985 with bulk samplers (custom made). From 1989 onwards, wetonly samplers were used exclusively (ANTAS, Institute of Energetics, Leipzig), and as of 1998/1999 wet only samplers by Eigenbrodt. In the Erzgebirge, the measurements began at Marienberg in the central Erzgebirge and at Zinnwald in the eastern Erzgebirge. The network was extended in the early 1990s by the station at Carlsfeld, western Erzgebirge, and later by one near Mittelndorf. Likewise, wet-only samplers (Eigenbrodt) were used by UBA at Luckendorf . since 1992, and at Lehnmuhle . as of 1993. Starting 1984/1985, monitoring stations to assess atmospheric deposition on forest ecosystems were exclusively operated by the TUD, in the upper eastern Erzgebirge (OBB), and in the Tharandt Forest. Starting 1990, yet another station was established in Carlsfeld. The equipment consisted of automatically operated wet-only samplers (ANTAS,

Institute of Energetics, Leipzig) and bulk samplers (custom-made) for total deposition. Within the framework of the EU-Level II programme, the network was considerably extended by the Regional Office for Forestry in Graupa (SLAF). This was supplemented by one station each in the western Erzgebirge near Klingenthal, in the eastern Erzgebirge near Olbernhau and in the transitional area to the Elbe sandstone mountains near Cunnersdorf. Since 2000, a new site was established near Altenberg, eastern Erzgebirge. These data sets are supplemented by series started in 1983, focussing on the input of heavy metals and fluorides. Again, TUD initiated monitoring efforts located along the southern border of Saxony, from the Central Erzgebirge up to the Zittau Mountains (Table 1, Fig. 1). This work was soon complemented by detailed dry (low volume samples, Derenda, Berlin) and total deposition (custom made bulk samplers) research with a very broad array of elements (Matschullat et al., 1995; Matschullat and Bozau, 1996; Matschullat and Kritzer, 1997).

2. Gaseous atmospheric compounds The three major gaseous pollutants are sulphur dioxide (SO2), nitrogen oxides (NOx: NO, NO2) and ozone (O3). 2.1. Sulphur dioxide In the Erzgebirge, SO2 is the prominent atmospheric pollutant in respect to its emission history, its ambient concentration, and its effects on ecosystems. The gas has an atmospheric lifetime of several days. With an average wind speed of 4 m s 1, the gas will be transported over some hundred kilometres prior to deposition or oxidation to sulphate. Most of the anthropogenic sulphur is released in the atmosphere by fossil fuel combustion. The large power plants in Southern Saxony and Northern Bohemia are exclusively based on the combustion of lignite with partly high sulphur content from pyrite (FeS2). The average sulphur content of Saxonian lignite is 1,7% (Leipzig basin; Just et al., 1986) and 0.5–1% (Lusatia; LAUBAG, pers. comm.), and in the Bohemian basin from 0.5 to 5.75% (Sulovsky, pers. comm.). Until 1990, most regional power plants worked without desulphurisation and dust removal. Following the German re-unification, many factories and power plants were shut down or modernised. This lead to emission reductions of about 92% in Saxony (baseline 1989; Fig. 2). 2.1.1. Air concentrations—historical data The first regional data on atmospheric SO2-concentrations were presented by D.assler and Stein (1968,

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675

2500

SO2-emission [kt a-1]

2000

1500

1000

500

0 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 year

Fig. 2. SO2-emissions in Saxony from 1986 to 1999 (LfUG, 1997b, 2000).

Table 2 Annual SO2-means (mg m 3) for various Erzgebirge sites from 1968 to 1972 (Auermann and Kneuer, 1977) Location

1968 1969 1970 1971 1972 1968–1972

Western Erzgebirge Oberwiesenthal

11

60

60

80

53

Central Erzgebirge . Johstadt Pockau 58 Reitzenhain

43 70 42

85 132 92

103 128 135

98 90 87

82 96 89

Eastern Erzgebirge C.ammerswalde Deutscheinsiedel 58 Sayda 78

63 60

75 94 100

70 98 88

57 62 80

67 81 83

1972) and by Auermann and Kneuer (1977). Table 2 shows the annual SO2 mean concentrations by Auermann and Kneuer from 1968 to 1972. For comparison, the five-year mean value (1966–1971) by D.assler and Stein (1972) for the area around Rubenau . (Central Erzgebirge) is 60 and 90 mg m 3 for Rehefeld (Eastern Erzgebirge). These early measurements point to a shift from the initial impact area around Deutscheinsiedel (mainly due to the chemical works Zalusi near Litvinov) in a westward direction to a . new area around Reitzenhain, Johstadt. This shift is a result of distant emission sources that temporally coincide with the construction of new power plants (e.g. Tusimice with a 200 m high smokestack). Starting

1970, following the start-up of the industrial unit VRESOVA near Karlovy Vary, a distinct SO2-concentration increase occurred around Oberwiesenthal, Fichtelberg (Table 2). These results were confirmed by measurements from the 1960s and 1970s. Major centres of air pollution occurred around Deutscheinsiedel/Deutschneudorf in the Einsiedler saddle, and on the Czech side, Nova Ves v horach and Mnisek, as well as in an area of the Central Erzgebirge starting from B.arenstein and Veiperty in the . Czech Republic, via Johstadt, Satzung, Hirtstein, Reitzenhain, Kuhnhaide . to Rubenau, . with annual means exceeding 120 mg SO2 m 3. The area of Kahleberg in the Eastern Erzgebirge was slightly less polluted, with annual means around 80 mg m 3. A first air pollution map of the area was delivered by Liebold and Drechsler (1991; Fig. 3). Oberb.arenburg registered the input of noxious substances, and discontinuously measured SO2-concentrations from November 1986 to October 1987. In this period, the mean SO2-concentration was 55 mg m 3 (Zinnwald: 80 mg m 3). The half-hour maxima reached 950 mg m 3 in November 1986. Table 3 shows the OBB monthly means in comparison with data from Zinnwald (restricted to data recorded simultaneously at both stations). At OBB, located leeward from the eastern slope of mount Kahleberg, the SO2-concentrations were considerably lower than at Zinnwald, most pronounced when diurnal values exceeded 100 mg m 3 at Zinnwald. During periods of a low air mass exchange, however, higher SO2-concentrations were measured at OBB. The results of the SO2-monitoring network, established after 1990 are summarised in Table 4.

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SO2-concentration (mg m-3) 0.055 0.065 0.085 0.090 0.100 0.120

Fig. 3. Annual average SO2 concentrations (mg m 3) in Southern Saxony (Liebold and Drechsler, 1991; data from the 1980s).

Table 3 Monthly SO2-means (mg m 3), at Oberb.arenburg, OBB, and Zinnwald, ZW (1986/1987)

November 1986 December 1986 April 1987 May 1987 August 1987 September 1987 October 1987

OBB

ZW

88 71 48 37 46 53 47

101 69 101 78 52 118 45

Until 1996, there was no significant SO2-decrease in the upper Erzgebirge as compared to other areas of Saxony. At these higher altitudes, episodes of very high pollutant concentrations still occurred, mainly due to SO2-emissions from the N-Bohemian industrial region. The Central Erzgebirge, followed by its eastern part, was most severely affected by air pollution whereas the Auersberg region in the Western Erzgebirge received comparatively low pollution levels. Extremely high SO2-concentrations of several 100 mg m 3 have been observed in the Erzgebirge, when the respective measurement was made downwind from an emission trail of a power station, typically extending a few kilometres. Concentration maxima are dependent on wind dynamics and thus, considerable horizontal concentration gradients may occur (Beyrich et al., 1998). From 1996 to 2000, the SO2-concentrations declined drastically, following the modernising of the N-Bohemian power plants (Table 4). In the last few years, annual SO2-means reached levels between 5 and 10 mg m 3. A similar trend was observed for peak

concentrations. The 98th-percentile of SO2 reached 70 mg m 3 in the year 2000 (LfUG, 2001). 2.1.2. Mobile measurements From 1983 to 1996, a mobile SO2-monitoring network operated in southern Saxony (Reuter and Wienhaus, 1995). Measurements were made at 40 selected locations in the central and eastern parts of the Erzgebirge, in the Elbe sandstone mountains, and the Zittau Mountains. Short interval measurements took place discontinuously during the growing season from May to September, weekly and randomly regarding wind direction and weather situation. Forest/crop field boundaries and, partly, forest sites (remote from settlements) were selected as locations of the measuring points. The DESAGA gas sampler served as a direct measuring instrument. SO2 is absorbed, using sodium tetrachloromercurate (II) (TCM), and colorimetrically determined using pararosaniline. Based on mean values, results from the mobile equipment (Table 5) were only partly (Eastern Erzgebirge) comparable with those from stationary measurements (Table 4), due to the discontinuous character of the mobile records. These mobile measurements underlined the relevance of distinct source areas as derived through a differentiated analysis of wind directions (Wienhaus et al., 1994; Table 6): 1. The highest SO2-concentrations in the Central and Eastern Erzgebirge and the adjoining Elbe sandstone mountains occurred with SE winds. The influx from the N-Bohemian lignite mining centre was obvious. 2. SW winds are of relevance for the same area. Its mountainous relief led to an air pollution impact, specific for the industrial emissions from N-Bohemia.

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Table 4 Annual SO2-means (mg m 3) in the Erzgebirge from 1991–1995, and 1996–2000 Western Erzgebirge

Central Erzgebirge

Year

Carlsfeld

Fichtelberg

B.arenstein Annaberg Olbernhau Zinnwald Oberb.arenburg Lehnmuhle . Tharandt forest

1991 1992 1993 1994 1995 1991–1995 1996 1997 1998 1999 2000 1996–2000

34 15 24 21 13 21 n.d. 11 6 4 4 6

44 24 28 31 31 32 37 20 10 7 6 16

107 70 86 66 55 77 73 31 13 7 8 26

a

Eastern Erzgebirge

123 80 78 68 51 80 59 21 10 6 7 21

95 73 78 67 42 71 54 28 15 9 n.d. 26

51a 59 50 38 35 49 30 25 15 7 n.d. n.d.

61 37 38 43 36 43 37 29 18 7 8 20

n.d. n.d. n.d. 32 36 n.d. 35 18 11 7 6 15

n.d. n.d. n.d. 36 26 n.d. 37 24 10 8 8 17

Altenberg; n.d.: no data.

Table 5 SO2 concentrations (mg m 3) in Southern Saxony from mobile measurements 1993–1996 1993

Central Erzgebirge Schwartenberg Eastern Erzgebirge Elbe sandstone mts., western Elbe river Elbe sandstone mts., eastern Elbe river Zittau mountains

1994

1995

1996

N

Mean

Max

N

Mean

Max

N

Mean

Max

N

Mean

Max

82 64 84 117 204 76

44 73 36 36 30 36

238 321 494 207 155 161

107 70 92 164 209 107

80 40 47 47 35 30

1322 204 426 540 205 239

118 49 61 144 160 96

35 70 40 32 24 30

234 380 212 540 241 606

119 62 81 138 197 80

28 26 26 25 16 14

209 123 328 130 64 82

Table 6 Total SO2-means in each respective year, compared with the individual SO2-means from selected wind direction sectors (all data in mg m 3) Year

Total

SE

SW

NW

NE

1993 1994 1995 1996

38 45 34 22

61 80 48 30

30 38 40 21

20 17 16 11

31 38 21 16

3. NE winds influenced the Zittau Mountains, and transported emissions from power stations of eastern Saxony and Silesia in Poland. 4. With the prevailing westerlies, low SO2-concentrations were recorded at all sites. Their mean values were below 20 mg SO2 m 3. Air pollutants from N-Bohemia played an important role until 1996. Their impact depended on the occurrence of heavily loaded air masses from SE, on inverted atmospheric conditions, on season and on relief

(mountain incisions). One of these events was measured in 1992 by the mobile Lidar system ARGOS (Advance Remote Gaseous Oxides Sensor) of GKSS research centre Geesthacht (Goers, 1994; Reuter and Wienhaus, 1995; Fig. 4). The SO2 concentration profile, measured in a southerly air flow from Schwartenberg to Einsiedler saddle (Erzgebirge ridge) revealed SO2-loaded air masses that move in a relatively thin layer of 200–300 m across the Erzgebirge crest. This may explain the temporarily low SO2-concentrations measured on the mountains, while at the same time very high concentrations were measured at lower locations and in the vicinity of cuts and hollows. 2.2. Nitrogen oxides Nitrogen oxides (NOx), consisting of nitric oxide (NO) and nitrogen dioxide (NO2), are mostly emitted as nitric oxide (> 90% of total) via anthropogenic combustion processes. NOx-emissions are high in and around cities und much lower in rural and remote areas like the Erzgebirge. Table 7 shows mean seasonal NO2data for different locations in Southern Saxony from

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2.3. Ozone

1992 to 2001. No long-term trend was visible in the 10-year period. Seasonal changes occured, with higher concentrations during winter and considerably lower ones during the vegetation period. In winter, heating power stations act as additional emission sources, also generating SO2-maxima. The NOx-concentrations in forest areas of Southern Saxony were not phytotoxic. The threshold in the growing season is given with 60 mg m 3 (WHO, 1987), or with an annual mean of 30 mg m 3 (Ashmore and Wilson, 1994). Thus, NOx may be interpreted as a ‘‘leaf fertiliser’’. With the prevailing low concentrations (NO 1–2 mg m 3, NO2 10–15 mg m 3), the risk for forest ecosystems is very limited. The ecotoxicological relevance is more relevant in the character of nitric oxides as precursor substances for O3-formation in the atmosphere.

Different from SO2 and NOx, high O3-concentrations were not only detected close to sources, but also in rural and remote areas (Table 8). Since 1988, the forest areas of Southern Saxony are exposed to increasing levels of photooxidants, supporting O3-formation over the summer months (mean values in summers 1981–1987 at Fichtelberg ca. 57 mg m 3, from 1988 above 80 mg m 3; unpublished data LfUG). Depending on meteorological conditions (radiation, general weather situation), fluctuations occur within individual years. Despite the relatively weak solar radiation and the cool summer of 1996, higher monthly O3-values were measured than in 1994 and 1995, which were both distinguished by record high temperatures and long periods of strong solar

Fig. 4. SO2 zenith scan by LIDAR (adapted from Goers, 1994). The profile was measured at location Schwartenberg (No. 10 in Fig. 1).

Table 7 Mean seasonal NO2-concentrations (mg m 3) at forest monitoring stations of Southern Saxony. Data from 1992 to 2001 Periode

Zinnwald

Schwartenberg

Oberb.arenburg

Lehnmuhle .

Tharandt forest

Winter Summer

17 11

16 10

15 11

15 7

13 9

Table 8 Mean summer O3-concentrations (mg m 3) in the Erzgebirge. Data from remote stations Station

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

Carlsfeld Fichtelberg Schwartenberg Zinnwald Oberb.arenburg Lehnmuhle .

— 92 — — — —

— 81 — — — —

64 69 — — 62 —

62 84 — — 55 —

77 — — — 83 70

80 83 — 79 77 74

76 86 — 75 73 72

86 94 — 90 90 72

85 95 80 83 84 68

88 99 88 91 — 73

85 96 85 88 — 74

82 94 82 83 — —

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radiation. So far, the highest O3-concentrations occurred in the summer of 1999 with a slight decrease in subsequent years. The critical O3-level for forests of 50 mg m 3 during the growing season (April–September; 7-h-value; UN-ECE (1988)-Critical Level has been exceeded at all stations for several years (Table 8). While the measured O3-concentrations are insufficient to cause direct damage on the relatively ozone-resistant spruce, more sensitive tree species such as beech, birch, oak, and pine, may receive acute damage during radiation-rich high-summer periods. This risk is underpinned by the new Critical Level of Fuhrer and Achermann (1994): AOT40-value of 10 ppm h >40 ppb ozone. At Oberb.arenburg, the AOT40 accounted for 18.7 ppm h in 1994, 17.9 ppm h in 1995, 12.4 ppm h in 1996, 21.2 ppm h in 1997, and 18.5 ppm h in 1998. Ozone thus presents the highest damaging potential of all gases for the Erzgebirge forest ecosystems. 2.4. HF and fluorine In the N-Bohemian industrial area, the SO2:HF ratio was 50:1. With emissions of e.g., 500,000 t SO2 per year (1996) about 10,000 t HF were emitted annually. Consequently, the high SO2-loads of the past, in winds blowing from southerly directions, were accompanied by high F -levels. The classical noxious substance ‘‘fluorine’’ embodies a damage-enhancing factor and most probably fluoride contributed to the forest damage of Southern Saxony (Wienhaus et al., 1992; Reuter et al., 1997). This became evident in the winter of 1995/1996 where major calamities with financial losses of ca. 50 Mio. Euro occurred in the upper Erzgebirge (Zimmermann et al., 1997). Declining SO2-concentrations led to declining F -inputs over the past few years (Table 9). From 1997 onwards, the concentrations no longer reached phytotoxic levels. It can be concluded from the decrease of SO2-emissions until today (2002), that this fact holds true for the following years. As shown above, F -inputs played a major role in explaining forest decline phenomena in the Erzgebirge. Phytotoxic concentrations were reached both in the gas phase and the particulate phase, due to high F concentrations in regional lignite. Their contribution to the extreme forest damage encountered in the winter of 1995/1996 could be shown by needle analysis (Fig. 5). Analogous to the SO2-decline, recent air chemistry

679

results demonstrate a distinct decrease of HF. Both air and needle concentrations are now below phytotoxic values.

3. Particulate atmospheric compounds Over the past years, atmospheric emissions in Central Europe decreased considerably (e.g. Matschullat et al., 1995, 2000; UBA, 1998). The most prominent examples are the declines of sulphur from point sources and of lead (Pb) from leaded fuels. While S-emissions declined simultaneously in Western and Central Europe and parts of North America (e.g. Dillon et al., 1988; UBA, 1998), the decrease of Pb-deposition was first observed in North America due to the earlier introduction of unleaded fuel (e.g. Eldred and Cahill, 1994; Mielke, 1997) and became apparent in Europe only after a 10-year delay (Schulte and Blum, 1997). Trends of other aerosol components are just as important, however, and sites with unusually high pollutant loading deserve special attention. 3.1. Aerosol concentration (low volume samplers) To assess the atmospheric aerosol concentration in the area, two aerosol samplers were deployed from 1992 to 1994 at the stations Zinnwald (ZI) and the Malter reservoir (MA) (Kritzer, 1995; Matschullat et al., 1995; Matschullat and Bozau, 1996; Matschullat and Kritzer, 1997). Comparable bulk deposition results between the stations Oberb.arenburg (OBB) and Zinnwald triggered the decision to combine forces of the two projects. The results have already been discussed in detail in this journal (Matschullat et al., 2000). A multi-element survey was carried out by Proton-induced X-ray spectrometry (PIXE), Instrumental Neutron Activation Analysis (INAA), and Graphite-Furnace Atomic Absorption Spectrometry (GF-AAS) for samples from 1992–1994 and 1996–1997 (Al, As, Ba, Br, Ca, Cl, Cr, Cu, Fe, Ga, Ge, I, In, K, Mg, Mn, Na, Ni, P, Pb, S, Se, Si, Sr, Ti, V, Zn). The results support the efficiency of emission control in Central Europe. The concentrations of many anthropogenic constituents in both bulk deposition and in aerosols today have declined considerably. In the formerly highly polluted Eastern Erzgebirge, particle deposition can now be addressed

Table 9 HF air concentration (mg m 3) in Deutschneudorf and Zinnwald in 1997 and 1998. Data from LfUG, 1997c, 1999 Site

02/1997

11/1997

12/1997

01/1998

02/1998

03/1998

Deutschneudorf Zinnwald

0.09 0.29

0.06 0.08

0.07 0.05

0.05 0.07

0.04 0.06

— 0.01

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F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691

Zittau Mountains Kahleberg Holzhau Zschirnstein Reitzenhain Satzung Rübenau Deutscheinsiedel 0

10

20

30

40 kg-1

Fluoride content in mg d.m. = dry matter growing season

50

60

d.m.

winter 95/96

Fig. 5. Fluoride contents in spruce needles 1995/1996 (needle age class 1995).

as comparable to rural areas without major local or regional influences. 3.2. Dust analysis (Bergerhoff method) Dust sedimentation measurements were performed since 1983 (Reuter et al., 1995). Locations remote from settlements and along forest-field boundaries were chosen. Measurements took place from May to October (growing season) with monthly sampling intervals. Tables 10 and 11 present selected results for fluoride and calcium. As of 1991, fluoride inputs strongly declined, but reached the old level once again in 1994. A completely different situation can be observed regarding calcium deposition. Calcium inputs vary between 3.5 and 6.9 kg ha 1 a 1 without spatial differentiation. The highest means were obtained from the Central and Eastern Erzgebirge, the Elbe sandstone mountains and the Zittau Mountains. A steady decline could be observed over the past years. While fluoride deposition will continue to decrease, calcium input is now influenced by the irregular liming activities to combat further forest soil acidification.

4. Precipitation and fog water A differentiation is made between occult (fog and cloud water) and wet (rain and snow) deposition. Wet deposition is particularly effective for atmospheric selfcleaning. It includes rainout: within-cloud scavenging

where aerosol-type air pollutants are incorporated in cloud droplets that can be transported over long distances—up to 1000 km—and finally precipitate as rain, and washout: below-cloud scavenging of dust and gases often close to an emitter. Under moderate climate conditions, rainfall occurs to about 10% of the total time. Between precipitation events, gases and dusts are deposited only in dry form on surfaces. This deposition is slower than by rain, depending on particle size and shape (turbulence-enhancing) and on surface conditions. Deposition is highest on conifers and open water surfaces. As air contaminants are efficiently withheld by the interception of canopy, forests are highly susceptible to atmospheric pollutants (acids, trace metals), and excess amounts or disproportional nutrient input (N, S, Ca). Rainwater chemistry changes, after passing a canopy, result from four different processes (Dambrine et al., 1998): (1) relative evaporative concentration of precipitation by the canopy; (2) older dry deposition washed off during the precipitation event; (3) leaching of organic and mineral compounds from leaf or needle surfaces, and (4) absorption of organic and mineral elements. The most important canopy transformations are direct assimilation of nutrients like N by the foliage or the phyllosphere microflora, H+ buffering, and leaching of basic cation, e.g. K+. Throughfall deposition thus represents the sum total of wet deposition, dry deposition of aerosols, cloud droplet deposition on leaf surfaces, and canopy interaction. The relative proportions of these processes vary largely with location. At lower sites it may rain for only

F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691 Table 10 Fluoride input in kg ha

1

a

1

681

(open field) in the Erzgebirge

Location

Until 1990

1991

1992

1993

1994

1995

1996

1997

1998

. Johstadt Central Erzgebirge Satzung, Central Erzgebirge Heidersdorf, Eastern Erzgebirge near Schwartenberg Liebenau, Eastern Erzgebirge

2.5 2.1 2.0 1.5

— 0.47 0.78 0.66

— 1.97 1.47 0.73

1.96 1.89 1.07 1.52

2.0 2.6 1.8 2.8

1.25 1.85 1.48 1.56

1.12 1.79 1.34 2.1

0.95 1.20 0.95 0.99

0.66 0.88 0.77 0.95

a

a

Measuring point at B.arenstein up to 1990.

Table 11 Calcium input in kg ha

1

a

1

(open field) in the Erzgebirge

Standort

Until 1990

1991

1992

1993

1994

1995

1996

. , Central Erzgebirge Johstadt Satzung, Central Erzgebirge Heidersdorf, Eastern Erzgebirge near Schwartenberg Liebenau, Eastern Erzgebirge

16.9 13.6 18.8 14.2

— 4.98 5.56 6.34

— 3.76 5.05 6.48

3.95 6.35 4.26 5.65

4.95 4.43 3.46 6.86

6.16 6.9 5.48 6.35

7.9 6.2 5.7 4.7

a

Measuring point at B.arenstein up to 1990.

7% of the time, so that dry deposition of S and N may make a significant contribution. Here, droplet deposition plays a minor role. Since wind speeds also increase with altitude, the efficiency of droplet impact on vegetation surfaces also increases. At higher elevation sites, the additional input by droplet deposition leads to an increase in water and element input. This is clearly visible with the throughfall data in Fig. 6, while the wet deposition does not change with altitude. The throughfall deposition indicates a strong increase in S-deposition with elevation, leading to roughly a doubling of throughfall S-deposition at the upper site compared to the lowest. In contrast, wet deposition of SO4-S does not increase significantly with elevation. A minor concentration enhancement was observed at the ridge site, mainly caused by the seeder–feeder effect (Fowler et al., 1989). The high elevation forests receive more precipitation than the forests at low elevation sites. For the time period 1985–2000, an interception loss of 47% was calculated for the lower site, while only 20% were measured at the upper site. However, this cannot be attributed only to the greater evaporation at the lower site. The rapid increase of fog events at the altitude of the inversion layer (700 m a.s.l.; Goldberg et al., 1998) contribute to the increase in water input on forest ecosystems. Throughfall measurements at OBB . and at Pobelbach (Bozau, 1995; Matschullat and Bozau, 1996) in May 1992–April 1994 showed significant differences in the chemical composition of throughfall precipitation (Fig. 7). While both sites are located at similar altitudes (735 m a.s.l. vs. 690–760 m a.s.l.), the . Pobelbach site was more influenced by the so-called ‘‘Bohemian fog’’, leading to higher SO4-S and F inputs.

SO42-- deposition (mol ha -1)

a

700 wet deposition throughfall

600 500 400 300 200 100 0 0

200

400 600 800 elevation (m a.s.l.)

1000

Fig. 6. SO24 -deposition (mol ha 1) in the year 2000 at four different elevations in the E-Erzgebirge.

4.1. Wet-only deposition The ion concentration of rainwater is an air pollution indicator. Therefore, changes in the precipitation chemistry indicate a change in emission pattern. A detailed presentation of the results of measurement by the MD monitoring network for the periods 1985–1989 . and 1990–1994 was given by Moller and Lux (1992) and by LfUG (1994, 1995). Table 12 shows the results of measurement obtained from monitoring stations in the Erzgebirge (kg ha 1 y 1). Additional results from wetonly samplers at OBB and Tharandt Forest for 1984– 1989 and 1990–1994 were published by Lux (1993, 1995). Again, the strong decrease of basic cations, and some of the anions is visible after 1990 (largely due to the implementation of modern filter technology in Saxonian power plants). The additional decrease of

682

F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691

Fig. 7. Throughfall deposition (kg ha

1

a 1) on two Norway Spruce stands in the Eastern Erzgebirge between 05/1992 and 04/1994.

S-emission from power plants in the Bohemian basin occurred after 1995 (Tables 12 and 13). Within the scope of the SANA project (SANitation of the Atmosphere above the new German states/Sanierung der Atmosphare den Neuen Bundeslandern), a wet. uber . . only sampler (ANTAS) was installed for daily sampling at Oberb.arenburg. Table 13 presents results for 1992–1995 (Bruggemann . and Rolle, 1998), 1996– 1998 (Zimmermann et al., 1998) and the year 2000 (Zimmermann, unpubl.). 4.2. Throughfall deposition Results from direct canopy throughfall measurements show a very high variability, both in respect to precipitation amounts and to the chemical composition of the water droplets. This variability requires the parallel use of different samplers. At each of the SLAF, TUD, and TUBAF monitoring sites, 15 inexpensive bulk deposition samplers were placed. While throughfall deposition is relatively easy to measure, the related data interpretation is a lot more complex due to the many processes that co-occur in the canopy. The longest data series were generated from sites operated by TUD at Oberb.arenburg and in the Tharandt Forest (Table 14). Results for the periods 1984–1989 and 1990–1994 have been published by Lux (1993, 1995). All data are differentiated by the respective stand age. In 1993, SLAF commenced its measurements at monitoring sites that are integrated in the Level II EU-Programme (SLAF, 1999; Table 15).

4.2.1. Spatial variability An E–W gradient of SO24 -deposition became apparent, related to the position of emission sources in the Eger graben, the orographic setting, and the meteorological conditions (dominating SW-winds). Both the stations Klingenthal (near Vogtland) and Carlsfeld (Western Erzgebirge) register significantly lower SO4-S, N, F , and acid input as compared to forests in the Central, and Eastern Erzgebirge. The higher precipitation amounts in the Western Erzgebirge slightly cover this effect. But even these western regions receive acid and N-inputs that exceed the critical loads. The highest inputs were measured in the Central Erzgebirge, enhanced during fog-rich periods at higher altitudes. The monitoring site Olbernhau is a hotspot, where dry SO2-S-deposition and SO4-S-fog deposition led to a throughfall input of 77 kg ha 1 a 1 during the hydrological year 1996. In the same period, 40–50 kg SO4S ha 1 were measured on sites in the Eastern Erzgebirge (Zimmermann et al., 1998). Further east (Elbe sandstone mountains), lower annual precipitation amounts and longer longitudinal distances to emission sources yield even lower inputs as compared with the Central Erzgebirge, but higher than those encountered in the Western Erzgebirge. The described East–West gradient is further differentiated by topography and altitude. Lower precipitation at lower altitudes and longer distances to the emission sources in the Bohemian basin, as well as the negligible input via fog and cloud water led to lower inputs. This is primarily true for SO4-S and F , and

F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691 Table 12 Wet only deposition at several stations in the Erzgebirge (kg ha Marienberg

pH Na K Mg Ca NH4 N NO3 N SO4 S Cl

1

683

yr 1)

Zinnwald

Carlsfeld

1985–1989

1990–1994

1995–1999

1985–1989

1990–1994

1995–1999

1992–1994

1995–1999

4.36 6.2 3 2.6 18 12 8.5 35 14.5

4.26 2 0.9 0.8 5.6 6.7 5.1 14.3 4.9

4.46 3.5 0.8 0.6 2.9 8.5 6.0 10.4 5.8

4.29 6.9 3 2.5 18 10 7.8 32 12.5

4.28 2.7 0.7 0.8 4.7 5.6 5.1 16 5.6

4.50 3.3 0.9 0.6 3.0 7.7 5.2 10.3 5.3

4.35 2.4 0.7 0.7 2.7 5.9 5.3 10.5 4.4

4.54 3.5 0.6 0.5 2.0 8.4 6.4 8.9 4.4

Table 13 Wet only deposition at Oberb.arenburg from 1992 to 2000 (kg ha

1

yr 1)

Oberb.arenburg

Precipitation (mm) pH Conductivity (mS cm–1) Na K Mg Ca NH4 N NO3 N SO4 S Cl

1992

1993

1994

1995

1996

1997

1998

2000

1088 4.5 37 6.5 2.3 0.7 5.3 8.7 5.9 15 5.4

1087 4.3 37 4.6 1.6 0.6 3.6 6.8 6 13.7 4.9

983 4.3 34 3.2 1.35 0.6 2.7 5.6 5.1 11.5 5.9

1306 4.3 30 3.5 0.8 0.7 2.3 7.5 6.5 13.9 6.8

946 4.4 24 2.6 1.6 1.0 3.9 7.3 5.7 8.1 3.0

962 4.6 23 3.7 0.5 1.0 2.8 6.9 5.2 7.4 5.0

1176 4.6 21 2.7 0.5 0.6 3.1 6.5 5.6 7.7 4.4

996 4.8 17 3.8 0.7 0.6 2.6 6.0 4.9 5.8 5.8

Table 14 Throughfall deposition mean values (kg ha year 2002 Years

P(mm)

SO4 S

Cl

1

a 1) for different periods at OBB, Tharandt forest and Carlsfeld. Stand age based on the NO3 N

F

NH4 N

K

Na

15.8 13.1 11.4 11

3.6 2.2 1.3 0.46

16.4 9.6 9.1 10.6

31.6 25.8 25.3 19.1

12 8 7.85 6.3

65.3 25.4 16.1 10.4

8.4 4.1 5.5 2.2

2.49 1.56 1.04 0.4

(b) Oberbarenburg, spruce mature timber (97 yr) . 92–94 846 65.5 18.5 20.2 95–97 847 39.9 17.4 17.7

2.1 1.5

13.4 14.6

20.7 18.2

12.3 11.1

26 19.8

6 7.6

1.69 1.12

(c) Tharandt forest, spruce mature timber (112 yr) 84–89 428 149.9 23.7 20.4 90–94 398 59.5 12.8 12.3 95–98 482 29.1 11.4 10.0 99–01 413 12.1 9.5 10.1

4.1 1.4 0.8 0.36

21.6 13.2 14.6 13.4

25.3 18.2 17.3 13.7

11 6.3 6.7 4.4

104.9 26.3 12 5.7

10.9 3.9 2.7 1.4

2.08 1.37 0.65 0.12

(d) Carlsfeld, spruce pole wood (48 yr) 92–94 876 44.5 11.6 95–97 1065 24.3 10.6

0.56 0.36

8.1 7.9

21.5 19.8

6.5 7.3

14.8 9.6

2.6 2.5

1.11 0.85

(a) Oberbarenburg, spruce pole wood (47 yr) . 84–89 817 104.5 23.8 90–94 749 65 13 95–98 848 37.2 12.2 99–01 728 21 11.7

8.3 7.7

Ca

Mg

H

F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691

684

becomes apparent with data from the Tharandt forest, gathered after the emission reduction measures within Saxony came into effect. The N-inputs deliver an even more differentiated picture. Local agricultural sources led to higher NH4-N-inputs in the lower-lying areas while the high altitudes show low NH4-N. As a consequence of traffic related NOx-emissions and their enrichment beneath the inversion layers (Zimmermann and Wienhaus, 2000), the lower altitudes receive higher NO3-N inputs (when evaluating throughfall deposition data it needs to be emphasised that only the lower input level of total N is represented because of the nonquantifiable amount of plant uptake). Fog and cloud water deposition have to be taken into account as a third type of atmospheric deposition at higher altitudes. While an increase of SO4, F , and acid inputs via ‘‘Bohemian fog’’ is characteristic on the Erzgebirge ridge (Bridges et al., 2002), cloud water is of high relevance for the input of NO3, Na+, and Cl at higher altitudes. Fog water measurements from OBB support this hypothesis, jointly with increased throughfall deposition of these ions from old spruce stands that more efficiently comb out fog than younger spruce stands. 4.2.2. Time-related variability Analogous to the emission development, three major time sections can be differentiated with throughfall deposition data: prior to 1990 with high air pollution, the years from 1990 to 1996 parallel to emission reduction measures in Saxony, and as of 1997 with a similar emission reduction programme for the large Bohemian power plants. Sulphate-sulphur: About 100 kg SO4-S ha 1 a 1 were deposited prior to 1990 at higher altitudes of the Erzgebirge, and about 150 kg SO4-S ha 1 a 1 at lower altitudes. In the following years, this load decreased to 60–65 kg SO4-S ha 1 a 1. Following the event period of 1995/1996, partly with loads of 80 kg SO4-S ha 1, emission reduction measures in Northern Bohemia

decreased to ca. 35–30 kg ha 1 a 1 in 1997/1998. In 2001, about 20 kg ha 1 a 1 were measured at higher altitudes, and at lower altitudes loads of 10– 12 kg ha 1 a 1. This reduction of 80–90% (based on the mid-1980s) can be seen as a major success story of environmental management. A similar reduction is visible with fluoride and acid inputs. Nitrogen: Based on the data from the mid-1980s, both NO3-N and NH4-N deposition showed a certain decline (shut-down of outdated industrial units, reduction in agricultural production). In the 1990s, a minor decrease of NO3-N is measurable despite a strong growth in automobile numbers. At the same time, NH4-N input stagnates both on high and lower altitudes at 10– 15 kg NH4-N ha 1 a 1. Thus N-input remains a serious threat for the stability of spruce ecosystems in the Erzgebirge. Base cations: The input of base cations in throughfall deposition results from two different sources, total deposition (wet + dry + interception), and internal leaching. The latter is the dominating mechanism for K+. The leaching efficiency depends on ambient SO2concentrations (Slovik et al., 1996) and on precipitation, because K+ is highly mobile and present as an electrolyte within the plant. The SO2-decrease consequently led to a reduction of K+ input. Observed variations were simply related to precipitation variability. Different from K+, both Ca2+ and Mg2+ are bound to plant tissue and are being exchanged via ion exchange processes against protons. Lower pH-values thus lead to higher leaching rates. Thus, the drastic reduction of Ca2+ and Mg2+ deposition is not only related to a reduction in dust emissions but to the increase of pH-values in precipitation. During 1996 and 1997, widespread liming of forest soils with ground dolomite momentarily led to higher Ca2+ and Mg2+ deposition. Sodium is not easily leached. The reduction of Na+ and Cl inputs as of 1990 is probably related to a shift from salt rich coal to salt poor varieties in regional power plants.

Table 15 Annual element fluxes at the Saxonian SLAF level II survey sites (kg ha

+

H K Ca Mg NTotal SO4 S

1

yr 1)

Klingenthal

Olbernhau

Cunnersdorf

840 m a.s.l., Norway spruce

720 m a.s.l., Norway spruce

440 m a.s.l., Norway spruce

1994

1995

1996

1997

1995

1996

1997

1994

1995

1996

1997

1.51 17.3 9.9 1.4 20.3 35

1.6 24 12.2 2.5 23.8 39.4

2.48 19 10.2 1.5 22.4 37.0

0.89 14.8 13.0 3.5 18.9 24.4

2.07 34.4 17.4 3.7 28.0 66.7

4.05 31.2 18.9 4.5 46.7 77.1

1.77 14.7 12.6 3.3 35.4 33.3

1.77 14.6 11.1 1.9 27.6 46.1

1.51 18.7 11.6 2.9 26.3 44.2

1.67 16.2 10.3 2.1 31.4 41.9

0.77 11.0 8.7 1.9 25.2 24.9

F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691

4.3. Fog and cloud water The relevance of fog and cloud water for the hydrological budget of forest ecosystems has been known for a long time. In particular at sites above 600 m a.s.l., part of the precipitation input and thus also of the element input originates from fog and cloud scavenging. The ecotoxicological relevance of occult deposition results from the drastically elevated element concentrations in fog droplets. The concentration of pollutants like SO2 and NOx in fog and cloud water may exceed that in rain water by two orders of magnitude. Under extreme conditions, the formation of strong acids like H2SO4 und HNO3 may lead to pH-values below 2.0 (Sigg et al., 1987). While such low pH-values

Idar-Oberstein / Hunsrück

120

SO4-S

100 kg*ha-1*a-1

Ca

80

NO3-N NH4-N

60 40 20 0 1984-1989

1990-1994

1995-1998

1999-2000

Oberbärenburg / Erzgebirge 120 SO4-S

100

kg*ha-1*a-1

Regional variability with time: In Germany, a dense network of monitoring stations for atmospheric gases and depositions exists since the early 1980s. To demonstrate major differences in air pollution between eastern and western parts of Germany, throughfall deposition data of SO4-S, Ca, NO3-N, and NH4-N at OBB are compared with those from Idar-Oberstein (Fig. 8). Idar-Oberstein is situated in the Hunsruck . forest (Rhineland-Palatinate), about 500 km west of the Erzgebirge, close to the French border. Like Oberb.arenburg, the Idar-Oberstein site features a high elevation forest (660 m a.s.l.) dominated by spruce (130 years old). The striking feature at Oberb.arenburg are the S and Ca2+ reductions of 80% and 85%, respectively, since 1984. In W-Europe, air pollution prevention measures were carried out earlier than in former EEurope. Moreover, the use of lignite was not that common in the West. Therefore, significantly lower deposition rates were measured in 1984 at IdarOberstein. Deposition rates of 33 kg ha 1 a 1 for S, and 16 kg ha 1 a 1 for Ca2+, respectively, were about 3–4-times lower than at OBB. These atmospheric inputs were still high enough; however, to cause severe tree damages in W-Europe. From 1984 to 2000, the S and Ca2+-deposition rates decreased by 50–40% at IdarOberstein. Current values at OBB and Idar-Oberstein are in the same order of magnitude. Sulphur deposition (21 kg ha 1 a 1) at OBB still exceeds that at IdarOberstein (16 kg ha 1 a 1). This difference may be due to a local household consumption of lignite, primarily in the winter season. Nitrogen deposition rates display a different story. Compared to S and Ca2+, the deposition varied in a narrow range only. From 1984 to 1994, the total Ndeposition declined from 32 to 21 kg ha 1 a 1 at OBB, while Idar-Oberstein shows no changes. As of 1995, both sites display similarly constant values for NO3-N and a continuous increase for NH4-N. A decade after German re-unification, atmospheric deposition rates become uniform, too.

685

Ca NO3-N

80

NH4-N

60 40 20 0 1984-1989

1990-1994

1995-1998

1999-2001

Fig. 8. Throughfall deposition (kg ha 1 a 1) between 1984 and 2001 for a forest site in Rhineland-Palatinate* (Idar-Oberstein, 660 m a.s.l.) and in Saxony (OBB, 735 m a.s.l.). *source: Forstliche Landesversuchsanstalt Rheinland-Pfalz.

have not been observed in German forests, evaporation of intercepted fog water leads to more acidic solutions on the leaf surfaces of plants (Frevert and Klemm, 1984). 4.3.1. Erzgebirge First measurements of the elemental composition of fog water began in the 1950s in the Eastern Erzgebirge (Mrose, 1961) and were resumed in the 1980s (Zier, 1991). More detailed studies of the chemical composition of fog and cloud water and their additional water input in the Eastern Erzgebirge followed in the late 1990s (Zimmermann and Zimmermann, 1999, 2001, 2002). Time series from weather stations in the Erzgebirge show a significant dependence between the number of days with fog, and altitude. The average annual number of days with fog occurrence varies between 50 at elevations of 500 m a.s.l. and up to 300 at the Fichtelberg (1214 m a.s.l.). In the Eastern Erzgebirge, the annual number of fog days amounts to 200 at 900 m a.s.l. (Zinnwald). The input of fog and cloud water in spruce stands reaches 20 mm in the Tharandt forest, 100 mm at higher altitudes, and 200 mm at the Erzgebirge crest (Flemming, 1993a, b). Wind exposed sites at the ridge may well receive up to 500 mm yr 1. Model calculations for the Fichtelberg area yielded an additional 1000 mm yr 1 (Zimmermann and Zimmermann, 2002). Mean volume-weighted ionic

686

F. Zimmermann et al. / Atmospheric Environment 37 (2003) 671–691

concentrations of fog and cloud water samples are presented in Table 16 (Zimmermann and Zimmermann, 2001). At both experimental sites, ZW and OBB, ionic concentrations were up to 25 times higher in fog and cloud water than in wet deposition. The median pHvalue in fog was 4.0 (minimum pH 3.3). The chemical composition of fog differs between sites. The ridge is strongly influenced by the so-called ‘‘Bohemian Fog’’. Dominant species in the fog water were SO24 and NH+ 4 . Compared to rain, relatively high F -concentrations were observed (41 meq l 1, OBB rain/snow 1.1 meq F l 1 in the year 2000). In contrast, fog water composition at the upper sites were dominated by NO23 (988 meq l 1), and high concentrations of Na+ and Cl . This may be caused by the dominant front fog at this site and enrichment of traffic emissions in the inversion layer. For the ridge sites in the Eastern Erzgebirge, a mean additional water input by fog deposition of 165 mm was calculated with a deposition model (Pahl, 1996). For a 40 year old spruce stand, 60 mm of additional water input through fog deposition were calculated by a canopy water balance model. One hundred millimetres were calculated for a 100 years old spruce stand at the same site. Obviously, fog deposition depends on stand height and slope exposition. Table 17 summarises the S- and N-input via wet, fog and throughfall deposition in the hydrological year 2000 at OBB for the 40 years old spruce stand (Zimmermann and Zimmermann, 2001). In the year 2000, the mean value of SO2-concentration at OBB was 8 mg m 3. With an estimated deposition velocity Vd of 0.8 cm s 1 for the younger spruce stand, a dry deposition of 10 kg SO2-S ha 1 yr 1 can be calculated. The calculated sum of wet, fog and dry S-deposition agreed quite well with the measured S-deposition by throughfall. For N, the calculation led to an overestimation, which might be due to direct absorption and biological uptake of N-compounds in the canopy. 4.3.2. Comparative data Only few long-term data sets for fog water composition in Germany are available. At Mt. Brocken (Harz mountains, 1142 m a.s.l.), routine sampling of cloud . water has been executed since 1991 (Moller et al., 1996; Acker et al., 1998). Only recently, a fog study was conducted at the research site Waldstein (Fichtelgebirge, 786 m a.s.l.; Wrzesinsky and Klemm, 2000). Table 18 lists the results of these studies for the years 1995–1997. At all sites, the mean ionic concentrations are in the same order of magnitude or fit in the range of maximum and minimum values, respectively. Fog water composition was dominated by SO24 , NO23 and NH+ 4 . These ions contribute to about 70–90% to the total ionic charge. Some differences are obvious between the sites. Sulphate and NH+ 4 -concentrations are somewhat higher

Table 16 Mean volume-weighted ionic concentrations [meq l 1] of fog and cloud water at the sites Zinnwald (877 m a.s.l.) and OBB (735 m a.s.l.). Values rounded for clarity Site Time period

Zinnwald Zinnwald December 1997– October 1998– May 1998 April 1999

Oberb.arenburg October 1999– May 2000

pH SO24 NO3 NH+ 4 Na+ Cl

4.0 560 180 560 52 48

3.8 440 990 640 388 393

4.0 570 200 630 26 27

Table 17 Deposition of S and N-compounds at OBB for the hydrological year 2000 (kg ha 1 yr 1)

P (mm) SO4 S NO3 N NH4 N

Wet

Fog

Throughfall

1085 5.9 5.0 6.9

45 3.2 6.3 4.1

878 19.1 11.0 11.4

for the Erzgebirge and Waldstein than for the Brocken site (Tables 16 and 18). This may be due to the fact that these sampling sites are more often influenced by air masses from Eastern and Central Europe with higher SO2 content. Mt. Brocken cloud water chemistry shows a considerable variation. While the data sets from 1995 and 1996 (Acker et al., 1998) correspond well, a 2-and 6-fold lower ionic concentrations was measured in 1997 (Plessow et al., 2001). The data from 1997 represent only a short period of time of Mt. Brocken cloud water chemistry, whereas the samples of 1995 and 1996 were collected from April until October. Thus, the results underline the large variations which occur in fog and cloud water compositions depending on liquid water content, formation of fog water, surface interactions and air mass origin.

5. Synopsis Based on the experience of the past decades it becomes obvious that a complex problem such as air pollution and atmospheric deposition requires a broad systems approach in order to (a) properly understand the underlying processes, (b) deliver a sound interpretation of data and observed phenomena, and (c) to work at finding sustainable solutions for the encountered problems. The following paragraphs sum up the experience.

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5.1. Gases 5.1.1. Sulphur dioxide Until 1990, SO2-concentrations in forested areas of the Erzgebirge were between 80 and 120 mg m 3. This concentration declined to 30–40 mg m 3 in the mid1990s. Further emission reductions led to a continuing reduction over the last 5 yr. Today, the annual average mean concentration is 5–10 mg SO2 m 3 air. These concentrations do not show phytotoxic effects. Even short-time concentration peaks of several-hundred micrograms of SO2 do not exceed the detoxification capacity of an SO2-sensitive tree species like spruce (Slovik et al., 1992). 5.1.2. Nitrogen oxides During the 1990s, NO2-concentrations revealed little change at higher altitudes of the Erzgebirge. The annual means were 10–15 mg NO2 m 3 air. The phytotoxic potential of NO2 is smaller than that of SO2 und O3. No direct risk for forest ecosystems should be expected from the encountered concentrations. A more important aspect is the contribution of nitrogen oxides as O3precursor gases and their role as N-fertiliser in the Nlimited Erzgebirge forests. In more remote areas, NO can be detected in small concentrations only. Average concentrations are 1–2 mg m 3. Under inversion conditions and with long-distance transport from the Northern Bohemian basin, elevated concentrations may be encountered (Zimmermann and Wienhaus, 2000). The prevailing low concentrations and the low deposition velocity leads to a very limited risk for forest ecosystems.

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Table 18 Fog and cloud water chemistry (meq l 1) at different mountain sites in Germany Brocken

Waldstein

Time period

1995*

1996*

1997**

1997***

N pH SO24 NO3 NH+ 4 Na+ Cl

1340 3.8 320 364 468 117 110

2049 4.0 304 347 454 121 118

60 4.3 125 122 198 23 18

56 4.3 497 481 669 65 54

*Acker et al. (1998); **Plessow et al. (2001); ***Wrzesinsky and Klemm (2000).

Phytotoxic concentrations were reached both in the gas phase and the particulate phase, due to high F concentrations in regional lignite. Their contribution to the extreme forest damage encountered in the winter of 1995/1996 could be shown by needle analysis. Analogous to the SO2-decline, recent air chemistry results demonstrate a distinct decrease of HF. Both air and needle concentrations are now below phytotoxic values. 5.2. Aerosol concentrations and deposition In general, the bulk of air pollutants is being washed from the atmosphere as wet deposition or deposited on vegetation surfaces as dry or interception deposition. Thus, the measurement of both open field and canopy throughfall deposition reveal valuable data to assess the development of atmospheric pollution.

5.1.3. Ozone Different from the situation in the 1990s at lower altitudes, O3-concentrations continuously increased at higher Erzgebirge elevations. While lower and middle altitudes show annual average concentrations of 50– 60 mg O3 m 3, averages of 70–80 mg O3 m 3 are typical for the higher altitudes. A slight decrease is noticeable in the last 2 yr (2000–2001). Emission reduction of the precursors NOx and VOC led to a decrease of O3 peak concentrations, and short-time peaks hardly exceed the threshold of 180 mg m 3. At the same time, the frequency of elevated concentrations (100–120 mg m 3) increased, however, and the number of O3-destroying situations (via NO) has decreased. Therefore, the changes are not reflected in the average concentrations. Thus phytotoxic thresholds, like AOT40, are being exceeded at all stations and in each year. Ozone thus presents the highest damaging potential of all gases for the Erzgebirge forest ecosystems.

5.2.1. Sulphate Parallel to the SO2-decrease in air, SO4-S-inputs have diminished both in open field and throughfall deposition. Extremely high SO4-S inputs of 30–35 kg ha 1 a 1 were measured in the field during 1985–1989. In the 1980s, the total input in pure spruce stands of ca. 100 kg ha 1 (80–120 kg ha 1) of SO4-S was caused by the filter effect of the forests. In the mid-1990s, about 10 kg SO4-S ha 1 a 1 were imported via wet deposition, and 40–50 kg ha 1 a 1 via throughfall. Today, open field deposition yields 5–7 kg ha 1 a 1 and throughfall deposition ca. 20 kg ha 1 a 1 at higher altitudes, 10–12 kg ha 1 a 1 at lower altitudes. Higher fog density and frequencies as well as wind speeds lead to increasing loads with altitude.

5.1.4. Hydrogen fluoride and fluoride dusts As shown above, F -inputs played a major role in explaining forest decline phenomena in the Erzgebirge.

5.2.2. Protons The decreasing trend in S-deposition is accompanied by a significant increase of pH-values in precipitation.

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The first determinations in the 1980s delivered average open field values of pH 4.3, and in throughfall pH 3.5. Today, open field precipitation shows pH-values of 4.8 and in throughfall 4.4 (higher altitudes) and 4.6 (lower altitudes), a noteworthy reduction in H+deposition. 5.2.3. Nitrogen Minor changes are being observed for N-inputs. While a slight decline can be seen for NO3-N in throughfall deposition from 13 kg ha 1 a 1 in the early 1990s to 10–11 kg ha 1 a 1 at the end of the decade (open field 5–6 kg ha 1 a 1), no such trend is visible for NH4-N. The respective values are 6–8 kg in open field an 11–15 kg ha 1 a 1 in throughfall deposition. 5.2.4. Base cations Corresponding to the drastic reduction of dust emissions after 1990 and the increased pH-values in precipitation, continuously lower base cation inputs are being measured in throughfall deposition. 5.2.5. Acid input and eutrophication Despite the good news above, the total acidic input, related to sulphur and nitrogen deposition still remains above the critical loads, tolerable for a sustainable development of the ecosystem (LfUG, 2001). This is similarly true for the eutrophying N-loads. Particularly threatened are nutrient poor forest soils at higher altitudes of the Erzgebirge.

Acknowledgements It goes without saying that such a review—although backed with many of our own data—could not be compiled and discussed without the numerous direct and indirect contributions of many colleagues that have or still do dedicate themselves to research in this area of Central Europe. We highly appreciate their comments and support and wish to thank every one of them. Two anonymous referees and the editor of this journal have spent a great deal of their time critically reviewing the first version of this paper. We are grateful for their very constructive criticism that has significantly improved the clarity of this paper. And last but not least, we wish to acknowledge the continuous financial support of several donor agencies that enable us to pursue our contribution for further improvements in air quality status in Europe. Current funding of BMBF under AFO 2000 is gratefully acknowledged. A special Thank you is extended to Dr. Harald Kohlstock from Freiberg University for his substantial support in upgrading the technical infrastructure at Oberb.arenburg.

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