6.1. Sulphur compounds

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6. Air Quality and Deposition Summaries, Local and Regional Air Pollution

In the following, air quality summaries are presented compound-wise: sulphur compounds, nitrogen compounds, black smoke, suspended particulate matter, ozone, lead, carbon monoxide. Only for sulphur and nitrogen compounds, regional data summaries are presented. For the other compounds, regional data of sufficient extent have not been available in preparing this report.


6.1. Sulphur compounds

6.1.1. Behaviour, effects, emissions

Sulphur dioxide (SO2) and particles emitted from the combustion of sulphur containing fuels are major air pollutants in urban areas, and SO2 is the principal pollutant associated with the acid deposition problem. Sulphur oxides and particulate matter are parts of a complex pollutant mixture, and are often considered together, since their effects cannot be distinguished from each other. In guidelines, the following categories are considered:

  1. sulphur dioxide
  2. acid aerosols from oxidation of sulphur dioxide
  3. sulphur dioxide plus particles.

In urban air dominated by local emissions, SO2 is the most abundant sulphur compound. Urban SO2 occurs in short term concentrations typically up towards several hundred µg/m3, and in extreme cases up to several thousands µg/m3. It is oxidised through several steps, via HSO3 to various forms of sulphates (sulphuric acid, ammonium sulphate and others). These reactions are fairly slow (in the range a few % per hour, dependent upon the composition of the ambient air). In highly polluted atmospheres, SO2 may enter into photochemical reactions, which are also rather slow. Removed from the vicinity of sources (as in regional air pollution), SO2 and sulphates often occur in concentrations of about equal magnitudes, in Europe up towards 30 µg/m3 as long term averages.

In periods with regionally poor dispersion and increased emissions, short term regional SO2 and particle concentrations may occasionally reach several hundred µg/m3.

SO2 and sulphates are removed from the atmosphere through wet and dry deposition, causing acidification of water and soil. Wet deposition of particulate sulphur dominates the total deposition.

Health effects of sulphur in air is caused by the absorption of SO2 on the mucous membrane of the nose and upper respiratory tract, and the deposition of sulphate aerosol in the respiratory tract. SO2 causes acute severe effects in the bronchii at very high concentrations (>10,000 µg/m3). Asthmatics experience effects at much lower concentration. Epidemiological studies indicate possible small reversible declines in children’s lung function at 250-450 µg/m3, and increased mortality at 500-1,000 µg/m3. Sulphuric acid cause human health effects, with a lowest demonstrated effects level of 100 µg/m3 on exercising adolescent asthmatics. High concentrations (>1,000 µg/m3) together with elevated particulate matter concentrations are believed to have been responsible for high mortality during smog episodes such as in London in 1952.

Acid deposition can affect terrestrial and aquatic ecosystems, if the deposition exceeds the critical load of the area. Effects include needle loss of conifers, and fish death. SO2 have a direct effect on vegetation at high concentrations (>some thousand µg/m3). SO2 plays an important role in the deterioration of stonework and metal corrosion.

Major SO2 sources in Europe are fossil fuel combustion for public power production and heating (54%) and small-scale heating (11%), industrial combustion (25%), and industrial processes (3%). (Percentage figures refer to the CORINAIR inventory, 1990).

The trend in SO2 emissions in Europe, as calculated for the EMEP area by the EMEP Meteorological Synthesizing Centre - West (Berge et al., 1995) is shown in Figure 6.1.


Figure 6.1: Emissions of sulphur dioxide in Europe, 1980-1993.
(Ref.: Berge et al., 1995).


The calculated emissions were 40% lower in 1993 than in 1980, and the downward trend has been fairly steady over the entire period.

For 1990, there was good agreement between the EMEP and CORINAIR emissions data for each of 23 European countries (Berge et al., 1995).


6.1.2. Air Quality Limit and Guide Values

The complete EU Limit and Guide values for SO2 with associated values for black smoke and suspended particulates are given in Table 6.1 together with Guideline values for Europe given by WHO.

Table 6.1: EU Limit and Guide Values for SO2 and associated values for BS (black smoke) and suspended particles (gravimetric) (µg/m3)
EU Council Directives 80/779/EEC and 89/427/EEC.
WHO Guideline values for SO
2 (µg/m3).

  SO2 Associated values for BS Associated values for suspended particles
Limit Values Median of
24 h values
98 percentile of 24h values Median of
24h values
98 percentile of 24h values Median of
24h values
98 percentile of 24h values
Year 80   >40   >150  
Year 120   <40   <150  
Winter 130   >60   >200  
(1.10.-31.3.) 180   <60   <200  
Year   2501   >150   >350
Year   3501   <150   <350
Guide Values Mean of 24h  values Maximum 24h average        
Year 40-60 100-150        
WHO Guideline Values Max. 10 min average Max. 1 h average        
Reference period not specified 500 350        

1 EU Member States must take all appropriate steps to ensure that this value is not exceeded for more than three consecutive days. More over, EU Member States must endeavour to prevent and to reduce any such instances in which this value has been exceeded.


WHO Guideline values for Europe for combined exposure to SO2 and particulate matter (BS, TSP or TP) (EHO, 1987).

 

Substance Mean values for averaging time
  24 h 1 year
SO2 125 50
BS1) 125 50
TSP2) 1203)  
TP4) 703)  

1) Black smoke

2) Total suspended particulates measured by high volume sampler without any size selection.

3) Value to be regarded as tentative at this stage.

4) Thoracic particles measured by a sampler having a 50% cut-off at 10 µm.

The WHO Guideline values are maximum values. They are not to be exceeded.


6.1.3. Urban and Local SO2 concentrations

Concentrations

SO2 data with associated values for black smoke and/or suspended particles from cities all over Europe are given in detailed tables in Appendix B. The data are from the APIS and EoI data bases and from national reports.

In Appendix B SO2 data from 17 countries are given. The stations are ranged according to the 98 percentile daily values. The stations with the highest values are given in Table 6.2. Also the maximum and median values are given, if available.

Figure 6.2 clearly shows the rather low concentrations in the Nordic countries. The highest 98 percentile and median values are observed in Germany (eastern part), the Czech Republic and in the Mediterranean countries.

Data from the selected cities in Figure 5.1/Table 5.2 are shown in Figure 6.3-Figure 6.6. These figures give the median, mean, 98 percentile and maximum values based on 24h values. These data indicate the highest SO2 levels in Germany and the eastern part of Europe.


Table 6.2: Maximum, 98 percentile and median SO2 values for 1993 for European cities ranged according to the 98 percentile values (µg/m3).

 

Country

 

Name

City
Class
 

Station

SO2 24 hour values
Maximum 98 percentile Median
Germany Chemnitz   Zwickau-Zentrum   570  
Germany Chemnitz   Chemnitz-Mitte 1   470  
Germany Leipzig   Leipzig-Mitte 2   460  
Germany Leipzig   Delitzch   410  
Germany Chemnitz   Chemnitz-Mitte 2   393  
Germany Dresden   Pirna   342  
Germany Greiz   Greiz   321 54
Germany Chemnitz   Plauen 2   317  
Germany Dresden   Dresden-Ost   281  
Germany Altenburg   Altenburg   270 42
Czech Republic Prague   Námesti Republiky 460 266  
Portugal Porto   Fac. Engenharia 266 257 25
Germany Weimar   Weimar, Goeth.   254 37
Germany Dresden   Dresden-Mitte   254  
Germany Dresden   Zittau-Ost   253  
Germany Leipzig   Leipzig-Mitte 1   250  
Germany Gera   Gera, Frieder.   247 45
Czech Republic Prague   Riegrovy sady 457 228  
Italy Porto Torres   Rio Mannu   223 6
Germany Erfurt   Erfurt, Krämpf.   222 28
Germany Dresden   Zinnwald   220  
Spain Madrid 1 Cuatro Caminos 288 216 41
United Kingdom Belfast 4 Belfast centre 354 213 29
Germany Cottbus 6 Cottbus-Süd 345 198 32
Czech Republic Prague   Pocernicka 442 194  
Germany Cottbus 4 Cottbus-City 375 192 23
Italy Genova   Enel 1 (Ponte Etiopia)   192 47
United Kingdom Liverpool 4 Liverpool centre 200 189 24
Germany Brandenburg 5 Brandenburg-Zentrum 235 184 21
Germany Dresden   Radebeul-Wahnsdorf   183  
Czech Republic Prague   Vysocany 524 178  
Czech Republic Prague   Výstavište 495 178  
Czech Republic Prague   Mlynárka   175  
Germany Braunschweig 4 Schlosspark 316 174  
Czech Republic Ostrava   Ostrava-Slez.Ostrava 433 171  
Czech Republic Prague   Veleslavin 513 170  
Greece Athens 1 Patission 147 327 170 52
Germany Braunschweig 4 Am Sackring 329 167  
Portugal Carregado   Faiel 210 165 9
Italy Siracusa-Augusta   Farodromo   164 20
Portugal Tapada Outeiro   Medas 502 163  
Germany Cottbus 5 Cottbus-LUA 292 162 17
Germany Eisenach   Eisenach   158 13
Italy Venezia (ind. zone)   Stab. Sirma   153 26
Germany Berlin   Charlottenburg 179 152 29
Germany Hannover 3 Welfenplatz 248 151  
Czech Republic Prague   Kobylisy 498 150  

Figure 6.2: 24h maximum, 98 percentile and median SO2 values for 1993 for selected stations and cities (µg/m3).

Figure 6.3: SO2 median 24h values in selected cities (µg/m3).


Figure 6.4: SO2 mean values in selected cities (µg/m3).


Figure 6.5: SO2 98 percentile values based on 24h values in selected cities (µg/m3).


Figure 6.6: SO2 maximum 24h values in selected cities (µg/m3).


Exceedances

Table 6.3 shows stations with exceedances of EU Limit Values for SO2 for combined exposure to sulphur dioxide and black smoke/particulate matter. Some other stations in eastern Germany, which have only reported 98 percentile 1/2h values, may also have 98 percentile 24h values above 250 µg/m3 . A few stations in Prague reporting 95 percentile 24h values probably have 98 percentile 24h values above the EU Limit Value. The available data statistics from national reports do not usually give (enough) information about exceedances of EU Limit Values.

Table 6.4 shows stations with exceedances of EU Guide values and WHO Guideline values for SO2 for combined exposure to sulphur dioxide and black smoke/particulate matter. Stations marked with * show exceedance of WHO Guideline values. Stations in bold show exceedance of the upper EU Guide value.

The table shows that a great number of European cities in many countries have mean values and especially maximum 24h SO2 concentrations well above EU Guide values and WHO Guideline values. Especially Czech values, but also some Germany values are very high.


Table 6.3: Exceedances of EU Limit Values for SO2.

 

Country

 

City

 

Station name

24h values
1 year 1 year Winter
Median
>80
P98
>250
Median
>130
France Lyon Lyon Berthelot 80    
Germany-Thüringen Altenburg Altenburg  

270*

 
  Greiz Greiz  

321*

 
  Weimar Weimar, Goeth.  

254*

 
Portugal Porto Fac. Engenharia  

257

 

* April 1993-February 1994.


Table 6.4: Exceedances of EU and WHO Guide Values for SO2.

Country City Station Mean
> 40-60
Max. 24 h
> 100-150
Czech Republic Ostrava Ostrava-Slez.Ostrava

56*

433*

  Prague Branik

54*

 
    Kobylisy

54*

498*

    Mlynárka

61*

 
    Námesti Republiky

103*

460*

    Pocernicka

66*

442*

    Riegrovy sady

73*

457*

    Santinka

52*

416*

    Veleslavin

57*

513*

    Vršovice

61*

441*

    Vysocany

70*

524*

    Výstavište

58*

495

France Lille Tourcoing  

116

  Lyon Croix rousse  

225*

    Lyon Berthelot

84*

225*

    Lyon Garibaldi  

168*

    Lyon Puits Gaillot

55*

 
    Saint Just  

268*

  Marseille Paradis  

133*

    Rabatau  

137*

  Paris Neuilly/Seine (92)  

154*

    Paris 13ème et.  

111

    Paris Ch. de Mars  

125*

    Paris Tour St-Jacques  

144*

  Strasbourg Hoerdt  

101

    Reichstett  

196*

    Rue du 22 novembre  

105

Germany Altenburg Altenburg

88*

 
  Berlin Charlottenburg

42

179*

    Frankfurter Tor  

174*

    Neukölen  

164*

    Schöneberg  

158*

    Wedding  

180*

  Brandenburg Brandenburg-Nord  

231*

    Brandenburg-Zentrum  

235*

  Braunschweig Am Fernmeldeturm  

343*

    Am Sackring  

329*

    Schlosspark  

316*

  Cottbus Cottbus-City  

375*

    Cottbus-LUA  

292*

    Cottbus-Süd  

345*

  Dortmund Dortmund-Asseln  

149*

    Dortmund-Hörde  

164*

    Dortmund-Mitte  

203*

  Duisburg Duisburg-Buchholz  

405*

    Duisburg-Kaldenhausen  

275*

    Duisburg-Meidenrich  

342*

    Duisburg-Walsum  

287*

      > 40-60 > 100-150
Germany (contd.) Düsseldorf Düsseldorf-Einbrungen  

191*

    Düsseldorf-Genresheim  

190*

    Düsseldorf-Lörick  

246*

    Düsseldorf-Mörsenbroich  

222*

    Düsseldorf-Reisholz  

218*

  Erfurt Erfurt, Krämpf.

68*

 
  Essen Essen-Altendorf  

234*

    Essen-Bredeney  

164*

    Essen-Leithe  

178*

    Essen-Ost  

420*

    Essen-Vogelheim  

398*

  Gera Gera, Frieder.

80*

 
  Greiz Greiz

117*

 
  Halle Halle

83*

509*

  Hamburg 06, LO Lokstedt  

192*

    09 RA, Rahlstedt  

179*

    11 HO, Hochkamp  

199*

    12 BA, Bahrenfeld  

223*

    13 ST, Sternschanze  

190*

    14 LS, Lübecker Strasse  

190*

    15 HR, Horner Rennbahn  

177*

    18 WA Waltershof  

210*

    19 SW, Steinwerder  

193*

    20 VE, Veddel  

209*

    21 BI, Billbrook  

180*

    26 KI, Kirchdorf  

166*

    27 Ta, Tatenberg  

190*

    30 GT, Göhlbochtal  

184*

  Hannover Fischeteichweg  

225*

    Göttinger Strasse  

214*

    Welfenplatz  

248*

  Köln Köln-Chorweiler  

166*

    Köln-Riehl  

178*

    Köln-Rodenkirchen  

246*

    Köln-Vogelsang  

230*

  Magdeburg Magdeburg

40

293*

  Rostock Rostock-Holbein Platz  

126*

  Saarbrücken Saarbrücken-Eschberg  

182*

    Saarbrücken-Stadtmitte  

183*

  Schwerin Schwerin (Burmeister-Bade-Platz)  

190*

    Schwerin-UBA  

246*

  Weimar Weimar, Goeth.

58*

 
Greece Athens Patission 147

62*

327*

    Pireas Platia Dinotikou

52*

170*

    Smyrni Cementry  

141*

      > 40-60 > 100-150
The Netherlands Ligging voor Achtergrondmetingen Zaaidijk-Axel  

127*

  Rotterdam Schiedamsevest  

110

  Sas van Gent Westkade  

221*

  Vlaardingen Floreslaan  

108

    Lyceumlaan  

135*

Portugal (contd.) Area Sines Santiago  

148*

  Barrero/Seixal Av. da Praia  

141*

    Camara Municipal  

100

  Carregado Cast. Ribatejo  

282*

    Faiel  

210*

    TAK  

102

    Vinha  

193*

  Estarreça Teixugueira  

158*

  Lisboa Beato  

126*

    Jerònimos  

133*

    R. Sèculo  

161*

  Porto Fac. Engenharia

50*

266*

  Setúbal Setenave  

151*

  Tapada Outeiro Aldeia Nova  

105

    Lever  

162*

    Lixa  

439*

    Medas  

502*

    Vila Cova  

171*

Slovakia Bratislava Karmenné námestic  

198*

    Marmateyova  

284*

    Trnavské mýto  

301*

    Turbinová

51*

301*

  Košice Podhvadová  

120

    Strojárenská  

137*

    Štúrova  

136*

Spain Barcelona Molina Pl.  

151*

    Prat del Llobregat

52*

123

  Bilbao Gecho  

114

    Lab. Sanidad  

158*

  Madrid Arturo Soria  

100

    Carlos V  

192*

    Cuatro Caminos

61*

288*

    Plaza Castilla  

108

    Plaza España  

167*

Tenerife   Santa Cruz

52*

256*

Switzerland Zürich Schimmelstrasse  

114

United Kingdom Belfast Belfast centre

48

354*

  Birmingham Birmingham centre  

144*

  Cardiff Cardiff centre  

101

  Edinburgh Edinburgh centre  

133*

  Leeds Leeds centre  

160*

  Liverpool Liverpool centre

40

200*

  London London Bloomsbury  

203*

  Newcastle Newcastle centre  

168*

Mean: *) > 50 WHO Guidelines Max: *) >125 WHO Guidelines.


Trends

Figure 6.7-Figure 6.10 show, as examples, trends in the SO2 data on an annual basis for some selected stations in different countries. The figures show the maximum, 98 percentile and median of 24 h values from Norway, Denmark, the Netherlands, Spain and Greece. German data (from Bremen) show 98 percentile and mean values based on œ h values, while Swiss data show 95 percentile and mean values based on œ h data. Each of the trend figures covers a part of the period 1976-1994.

Most stations show a downward trend in SO2-concentrations. The downward trend is very clear in Norway, Denmark, the Netherlands and Switzerland. In Germany (Bremen) and Spain the downward trend is less pronounced. In Greece (Athens) top values have increased and median and mean values have been rather stable at a relatively high level compared to other countries.

For East Europe there are no trend data available to us.


Figure 6.7: SO2 trend in Norway 1977-1993 (µg/m3). Data from national reports.


Figure 6.8: SO2 trend in Aalborg, Denmark 1983-1994 and Amsterdam, the Netherlands, 1976-1994 (µg/m3), APIS data.


Figure 6.9: SO2 trend in Athens, Greece 1983-1993 and Madrid, Spain, 1986-1993 (µg/m3), APIS data.


Figure 6.10: SO2 trend in Bremen, Germany, 1987-1993 and from Switzerland, 1984-1993 (µg/m3). Data from Bremen State and Swiss reports. The figures are based on œ h values.


6.1.4. Regional sulphur oxides concentrations and deposition

The EMEP measurement programme started in 1978. There were 99 monitoring stations in operation in 1993 in 26 countries. 77 stations reported precipitation data and 92 stations reported air concentration data during 1993.

A short description of the EMEP programme, including station list, is given in Appendix C.

The following presentation is based directly upon the 1993 EMEP data report (EMEP, 1995).


Data presentation

Annual averages of the 1993 air and precipitation data are presented in maps. The yearly precipitation mean concentrations are calculated from the daily values as precipitation-weighted averages. Average air concentrations are arithmetic averages of the daily means.


Kriging procedure

The concentration fields have been calculated using kriging methods. The EMEP grid is divided in 9 subareas. During the kriging process each area consists of 11x11 grid elements. In addition, 3 grid elements were added on each side of the sub-area in order to get an overlap and thus obtain a smooth concentration field for the whole area. After calculation on each of the sub-areas, consisting of 17x17 grid-elements, the results for each of the original 11x11 elements were concatenated to one 33x33 element concentration field. One grid element is 150 km x 150 km. In the kriging process, the averages are expressed through random functions. Separate calculations on nine subgrids rather than one calculation over a large grid area reduces the effects of the systematic concentration differences present in Europe.


Concentrations

Sulphur dioxide

The EMEP sites have been located away from local sources and are as far as possible representative for a larger region. One consequence of this is that the sulphur dioxide concentrations in Europe is higher in industrialised regions than the concentrations shown in Figure 6.11.

The lowest concentrations of SO2 during 1993 are found on the Atlantic coast in Ireland and in northern Scandinavia, where the averages are lower than 0.5 µg S/m3. From the United Kingdom eastward the concentrations increase from mainly 1–2 µg S/m3 to the highest SO2 concentrations measured in the network, in the area of eastern Germany, southern Poland, the Czech Republic, Slovakia and the north eastern part of Austria. In this region the annual average of SO2 in rural areas is above 5 µg S/m3, and peaks around 10 µg S/m3 are seen at one German and one Czech station. In Germany and Poland the concentrations decrease towards the north.

The concentrations of SO2 over the western part of Russia, the Baltic and southern Scandinavia are in the range 1 to 2.5 µg S/m3. Romania and Bulgaria do not take part in the measurements, and there is only one site in Greece. For this reason the kriged concentrations in this area are very uncertain and are thus removed from Figure 6.11. The situation is similar in the southern half of Italy. Relatively low concentrations are seen over France and central Spain.

The regional concentrations in central Europe (>10 µg SO2/m3, annual average) are higher than in most cities of Scandinavia and parts of North-western Europe.


Sulphate in aerosol

Figure 6.12 presents the annual averages of sulphate in aerosols in 1993. Large parts of Ireland and Scandinavia have averages lower than 0.5 µg S/m3. Towards south and east the concentrations increase to 1–1.5 in southern England to Denmark, southern Sweden and the Baltic. Most parts of western Europe experience concentrations in the range 1–2 µg S/m3. The highest concentrations are observed over south-eastern Europe, more than 8 µg S/m3 at one station in Greece and around 4 µg S/m3 at one station in Hungary. However, the sites in this area are relatively few and the inaccuracies are thus large. In Portugal and Spain the averages increases from 1–1.5 µg S/m3 in the north to 1.5–2 µg S/m3 in the south.


Figure .11: Sulphur dioxide in rural areas 1993, annual average (µg S/m3).
Factor 2.0.


Figure .12: Sulphate in aerosols 1993, annual average (µg S/m3).
Factor 3.0.


Wet deposition

Sulphate in precipitation

Sulphate in precipitation, corrected for sea-salt contributions are presented in Figure 6.13. As for most other pollutants of anthropogenic origin, the lowest concentrations are seen at the Atlantic coasts of Portugal and Ireland and in northern Scandinavia. Most of the Continent is exposed to annual averages less than 1 mg S/l. As for sulphate in aerosol phase, the region with higher concentrations stretch over the eastern parts of Europe, around 1.5 mg S/l or higher at stations in Croatia, Hungary, Poland and Yugoslavia. There is also a station in Ireland with concentrations at the same level. In Portugal and Spain there is a west to east increasing gradient, with a concentration of about 1 mg/l in the eastern parts.

pH in precipitation

The annual averages of pH in precipitation are presented in Figure 6.14. Over most parts of Europe the pH is lower than 5. The lowest pH values are seen in Poland and in middle Sweden; below 4.4, equivalent to an acid concentration of 40 µeql. Towards southern Europe there is in general an increase of pH.

Calcium in precipitation

Both industrial emissions of fly ash and other mineral particles, and soil dust are sources for calcium in precipitation, Figure 6.15. The high concentrations in southern Europe are mainly derived from soil dust, from wind erosion in the Sahara desert, and from local sources. The calcium content in both soil and rocks is high in many places in southern Europe. In eastern Europe industrial emissions, e.g. from cement plants, steelworks and power plants, give rise to concentrations of 10-20 µg/l of Ca in precipitation, while the concentrations of calcium in precipitation is low in the northern part of Great Britain and in most of Scandinavia and Finland. Calcium and other base cations increase the pH of precipitation.


Figure 6.13: Sulphate in precipitation 1993 (mg S/l).


Figure 6.14: pH in precipitation 1993 (pH units).


Figure 6.15: Calcium in precipitation 1993 (µg Ca/l).


Trends for the years 1985-1993

The EMEP Meteorological Synthesizing Centre-West (The Norwegian Meteorological Institute) has calculated sulphur reduction trends with distance from major emission sources for the period 1985-1993.

The EMEP-monitoring network have been classified into three broad groups. Stations have been grouped geographically according to the average straight-line distances of transport of deposition. "Long distance" sites are those lying approximately 1000 km or more on average from deposition quantity weighted sources, "medium distance" sites are those at between 500 km and 1000 km, and "short distance" stations are those under 500 km on average from sources. For sulphur dioxide, airborne sulphate, and sulphate in precipitation average monitored and modelled concentrations are plotted. The selection criteria for sites is as standard, i.e. that model and monitored results must be available on 25% of common days for precipitation results, and that air quality results must be reported for 75% of days. The further constraint is that stations must satisfy the criteria during each of the years. The time period considered is from 1985 to the end of 1993 for SO2 and SO4= in air, with 1992 the final date for sulphate in precipitation due to a lower number of stations reporting results at time of analysis.

Figure 6.16-Figure 6.18 show observed and modelled levels and trends of SO2 in air, sulphate in air and sulphate in precipitation.

The main conclusions from this trend analysis, are:

  • There is a downward trend for all the sulphur parameters.
  • Totally, there has been a close to 50% reduction from 1985 to 1993.
  • Both measured and modelled results show that the reduction has been largest for SO2 in air, about 60%.
  • The reduction has been the smallest for SO4 in deposition at sites far away from source areas, about 35% reduction.

The analysis show some discrepancies between the measured and modelled results.

It should also be noticed that the trend analysis has been done on a selected and rather limited set of sites (as shown in the figures), selected based on the criteria mentioned above. No analysis has been published on possible differences in trend between various parts of Europe.

The reduced SO2 concentrations in regional air over Europe coincides well, on the macro scale, with the reduced SO2 emissions described earlier in this chapter.


Figure 6.16: Time trend comparison for SO2 in air across the EMEP network.
a) Short distances from sources (<~500 km).
b) Intermediate distance (~500-1000 km).
c) Longer distances from sources (>~1000 km).


Figure 6.17: Time trend comparison for SO4= in air across the EMEP network.
a) Short distances from sources (<~500 km).
b) Intermediate distance (~500-1000 km).
c) Longer distances from sources (>~1000 km).


Figure 6.18: Time trend comparison for SO4= in precipitation across the EMEP network.
a) Short distances from sources (<~500 km).
b) Intermediate distance (~500-1000 km).
c) Longer distances from sources (>~1000 km).

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