ABSTRACT INTRODUCTION

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1 Concentrations of SO% and NO^ species over the Sudeten, Poland, during several field campaigns over a period of J.W. Zwozdziak, A.B. Zwozdziak Institute of Environment Protection Engineering, Wroclaw Technical University, Wroclaw, Poland ABSTRACT The results of several separately performed fields studies on air quality in southwestern Poland are presented. Under typical westerly wind conditions, this area is exposed to a heavily polluted air masses originating mainly in Central Europe. The results prove that even within the same air trajectory highly variable pollutant concentrations, particularly secondary aerosols, were monitored Thenhighest concentrations corresponded with ascending boundary layer air before the cold front. Some selected air quality parameters and meteorological factors have been subjected to the numeric-symbolic analysis and the results are discussed. INTRODUCTION The so-called Black Triangle covering substantial parts of Northern Bohemia (Czech Republic), Lower Silesia (Poland) and Saxony (Germany) is one of Europeas most infamous black spots and responsible for a significant part of the regional transnational air pollution in Europe The Karkonosze and Izerskie Ranges are located in the Sudeten, south-west Poland, in the middle of the Black Triangle. Under typical westerly wind conditions (prevailing SW-W directions) this area is exposed to polluted air masses originating in this part of the Black Triangle where extracting and power industries are concentrated. Excessive pollution loads have caused extensive damage to the forest ecosystem in the Karkonosze and Izerskie Mountains. In the Izerskie Mountains, which are the first barrier to air masses from western directions, more than 80% of trees above 900 m altitude have been destroyed.

2 262 Pollution Control and Monitoring Field measurements of concentrations of specified pollutants in the atmosphere and their precipitation have been undertaken since They were generally oriented to the empirical evaluation of trends and other aspects of spatial and temporal variability, to the determination of the pollutant fluxes reaching the region of interest and to the identification of important processes that were not anticipated prior to research activities. The results are published elsewhere [4] [6]. In this study, some of the most significant results from the measurements have been summarized. Some methods of data analysis have also been given into consideration. METHODS Aerosol samples were collected for 24 h during extensive weekly or monthly field investigations conducted over a period of at three sampling sites placed along the west slope of the Sudeten. Sampling sites No. 1 and No.2 were placed at the summits (1462 and 1362 m asl) of the Karkonosze Range. Site No 3 was located at the altitude of 650 m asl in the Izerskie Mountains. In total 360 aerosol samples were analysed for SC>2, NO%, total sulphur, sulphate and ammonium aerosol and total suspended participates (TSP). The existing monitoring stations were operated manually by means of the standard methods [3]. Only for total sulphur determination, a sampling set was designed. The unit comprised a prefilter (Whatman 41 of 47 mm diameter) for collecting the sulphate particles as well as a bubbler with slighty acidic hydrogen peroxide solution for the absorption of both SO2 and sulphate particles which have not been retained by thefilters.more details are given in the paper of Zwozdziak et al. [5]. Basic meteorological data were evaluated on the basis of on-site observations, others (e.g., mass category, weather conditions in central Europe, direction of air mass inflow at 850 mb) were collected by the National Weather Service in Wroclaw. RESULTS AND DISSCUSION In order to give an insight into the whole data base, in Table 1 there are summarized the daily SO2, NO%, sulphate and ammonium aerosols concentrations representing three sampling sites in a period of 5 years ( ). In the Table, a mean and standard deviation are comprised. The large variation in most of the data made it difficult to describe a "typical" exposure to pollutants in the region of interest, so a median was given. From the analysis of this basic statistical data it is evident, that the slightly elevated sites appear to be exposed to greater SO2 concentrations than the nearby sites of higher elevation.

3 Pollution Control and Monitoring (- «SC2 * NC2 -* NH<1 - SOd July, 1993»h July, July, 1993 Figure 1: Results of sequential sampling of some pollutants and measurements of temperature and humidity in the site placed 1362m asl

4 264 Pollution Control and Monitoring The distributions ofno%, sulphate and ammonium concentrations at the sites of higher elevation are not distinctly different from the distribution observed at the sites of lower elevation. Daily mean concentrations most of the species analysed varied from the minimum detectable level to the values higher than the critical level (permissible). Only NO% concentrations monitored were low. Table 1. Mean 24 hour concentrations of species measured ( s, jig/rrp ) standard deviation ( a, jug/m^ ) and median ( m, [ig/rrp ) Sampling site SO, s a m NO^ s am sulphate aerosol s a m ammonium aerosol s a m 1490m asl m ad m asl In many cases, individual concentration episodes were almost inpredictable and even unexplainable. Therefore, the meteorological conditions in the mountains were analysed thoroughly, not only in the day of measurements, but also in the days preceding and following them. Figure 1, for example, shows the results of a sequential sampling of SO%, NO%, total sulphur, sulphate and ammonium aerosol as well as measurements of temperature and humidity from 1st to 24th of July, 1993 at the place situated at 1362 m asl. It was a typical of this region period of cyclones crossing the Sudeten. Large fluctuations in the values of the concentrations measured do not seem unusual taking account of a long list of variabilites sources, associated with the influences of atmospheric advection and mixing processes as well as with mountain meteorology on air pollutant distribution. But the key feature is the pronounced variability of pollutant concentrations during increased atmospheric instability influenced by cold advection. The exhibited behaviour involved initial high concentrations of sulphate aerosol, increased concentrations of NO% and ammonium aerosol before a cold front passage followed by reduced values after the front passage. The SO% behaviour was just the opposite. There is also a substantial body of another field data which confirms this process. [7]. The measurements allowed us to arrive at a second major finding - there was a significant positive relationship between the ambient sulphate concentrations and NO% and ammonium ion levels, and a negative relationship between SO2 concentration. These relationships, common for some events, were not observed for all the cases. The calculated extent of SO2 conversion, amounting to 90%, allows the conclusion that the vertical mixing induced by large-scale lifting,and increased when synoptic scale flow is forced to rise as it encounters mountain barriers, creates favourable conditions for sulphate ion formation in the upper parts of the mountains. This process together with the increase deposition rate of aerosol

5 Pollution Control and Monitoring 265 on high elevation ecosystems [1][2] explain the forest damage which is being found particularly at the altitude ranging from 1000 to 1200 m asl. Daily measurements of air pollutant concentrations were arranged according to the wind direction as determined by 850 mb synoptic weather maps. Eleven wind sectors were established. Atmospheric advections from Germany are mainly comprised in the sector N-W., from Germany and Czech Republic - in the sector W-SW, from Czech Republic - in the sector SW-SE, from Czech Republic, Slovakia and Poland - in the sector SE-E and from Poland - in the sector E-N. The results, in terms of pollution rose, are presented in Figure 2. The results refer only to sulphur compounds and the sampling point situated 1362 m asl. It was found that the highest mean concentrations of SC>2 and sulphate aerosols were when the winds were blowing northwest-south directions. The percent distribution of wind direction reveals that easterly winds are very rare, therefore pollutant fluxes are mainly connected with westerly winds. It means that total sulphur flux entering the area investigated comes mainly from emission sources outside of Poland. N 20 pg/nf 2 Figure 2: Pollution roses for the sampling site placed 1362 m asl. As it has been mentioned before, changes in the concentrations of most pollutants investigated vary considerably from case to case. The investigations proved that even within the same air trajectory highly variable concentrations, particularly secondary aerosols, were monitored. The attempt to find a satisfactory correlation between the pollutant concentrations and meteorological parameters by means of statistical methods had failed. Thus, for the prediction purposes, the other manner of complex presentation of the investigation results was applied, i.e. approximation based on the chosen function class. We attempted to employ a numeric-symbolic analysis with respect to SO% and sulphate concentrations typical of those directions from which the most polluted

6 266 Pollution Control and Monitoring masses flowed, i.e. NW, W and SW. Our attention was concentrated on searching for the best approximation dependent on two parameters, temperature and humidity. There are no obstacles to analyse a large number of parameters in such a way; in that case, however, the graphic presentation of the results is a troublesome task. Hum, % 15 Temp.deg C Figure 3: Independent parameters analysed, i.e. temperature and humidity; advection from SW direction The basic idea of this kind of analysis is to take a list functions that you specify, and try to find a linear combination of them which approximates the data as well as possible. The goodness offitis measured by the quantify %2=Z I F ' fj 2, here Fj denotes the value of i-th data point and i fj is the value obtained from the fit. The best fit minimizes %%. As it is well known,polynominal fits are the most common. In Figure 4 there are presented for instance the points representing independent parameters, i.e. temperature and humidity, for which SO2 and sulphate concentrations were measured. The results refer only to the SW direction of air inflow and the sampling site placed 1362 m asl. This kind of analysis can be carried out within each range of the variables measured. However, taking account of a great diversity in description, which may occurs, in extreme cases such an analysis should be applied carefully. In Figure 4, there is presented the map of isolines representing sulphate concentrations, whereas in Figure 5 - the isolines of SC>2 concentrations obtained as a result of a mean square approximation. The extremal cases were excluded from the analysis. The approximation was done using polynominal fits

7 Pollution Control and Monitoring 267 S Figure 4: Isolines reprezenting sulphate concentration in air in the sampling site placed 1362 m asl. S Figure 5: Isolines representing placed 1362 m asl. SC>2 concentration in air in the sampling site

8 268 Pollution Control and Monitoring of sixth degree for each independent variable. Analysis of the figures allows the conclusion that in winter seasons the pollutant concentrations are higher than in summer seasons, and the most efficient SC>2 conversion is observed at temperatures close 0 C and humidity ranging from 80 to 95%. CONCLUSIONS The concentrations of all species analysed varied widely through the measuring periods. Even within the same air trajectory highly variable concentrations of secondary aerosols were monitored. In many cases ambient sulphate concentrations approached potentially harmful levels. The highest sulphate concentrations corresponded with ascending boundary layer induced by a moving forward cold front. High elevation sites appeared to be receiving comparable NO2 sulphate and ammonium aerosol exposure as the nearby lower elevations. The concentrations of SO2 at the summits were lower than below them. The strict formulas (in terms of mean-squere error) derived in order to present the distribution of sulphur compounds, for the chosen meteorological parameters, describe satisfactorily the phenomena analysed and can be considered as a basis for the estimation of these quantities in the future. REFERENCES 1. Choularton, T.W., Gay, M.J., Jones, A., Fowler, D., Cape, J.N. and Leith, L.D. "The influence of altitude on wet deposition: Comparison between field measurements at Great Fell and the predictions of a seeder-feeder model" Atmos. Environ, Vol.22,pp , Dore,AJ, Choularton, T.W., Fowler, D. and Storton-West, R. "Field measurements of wet deposition in an extended region of complex topography" Q. J. R. Meteorol. Soc., Vol. 116, pp , Harrison, R.M. and Perry R Handbook of Air Pollution Analysis - Chapman and Hall, New York and London, Zwozdziak, J.W. andzwozdziak, A, "Chemical composition of aerosol and rime ice samples collected at the summit of Szrenica, Sudeten, Poland" Wiss Umwdt. 3-4,pp.ll3-116, Zwozdziak, A, Kmiec, G. and Matyniak, Z " Penetration of atmospheric sulphates through cellulosefilters"j. Aerosol Sci., Vol. 22, pp , 6. Zwozdziak, J. and Zwozdziak, A. "Atmospheric sulphate formation and air pollution episodes in the upper parts of the Karkonosze mountains, Poland", Envir. Protec. Eng., Vol. 16, pp , Zwozdziak, J. "Concentrations of SOx and NOx species over the Sudeten during increased atmospheric instability" Arch. Ochr. Srodow., accepted for publication (in polish)