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Chemical composition of aerosol size fractions in Ljubljana
J. Aerosol Sci., Vol. 22, Suppl. 1, pp. $653-S656, 1991. Printed in Great Britain.
0021-8502/91 S3.00 + 0.00 Pergamon Press pie
CHEMICAL COMPOSITION OF AEROSOL SIZE FRACTIONS IN LJUBLJANA M.Bizjak, V.Hudnik, T.Raunemaa Boris Kidri~ Institute of Chemistry, P.O.B. 30 YU-61115 Ljubljana, Slovenia University of Kuopio, Department of Environmental Sciences, P.O.B. 1627 SF-70211 Kuopio
ABSTRACT Three sampling and analysis campaigns were performed in order to investigate mass size distribution and chemical composition of typical urban aerosol particles in Ljubljana. On the basis of obtained data particle size lnodes were identified with predominant part of accumulation mode. KEYWORDS Urban atmospheric aerosols; cascade impactor; size fractions; modal distribution; chemical composition
INTRODUCTION Air pollution situation in Ljubljana, relatively developed industrial and commercial centre of Slovenia with about 300.000 inhabitants, is well known problem first of all during winter seasons due to various emission sources (e.g. individual space heating stoves using coal and traffic), orography (city is located in a valley surrounded from three sides by hills and mountains), and meteorological conditions (temperature inversions, fog and cold periods). Many air situation studies and regular measurements were performed regarding gaseous and particulate pollutants, their chemical composition and the role in formation of secondary species, first of all sulphates (e.g. Bizjak et al., 1988). Less information was obtained about aerosol fraction composition (Berner et al., 1986). In the present paper we report on investigation of the chemical composition of aerosol size fractions collected during measuring campaigns near city centre. Results obtained by three different sampling techniques are compared.
$653
$654
M. BITAAKet al.
EXPERIMENTAL PART
Sampling Observation and measuring place of Hydrometeorology Institute of the Republic of Slovenia, located north of the city centre, about 500 m away from the main and 100 m from the local roads, was chosen for field experiments. Three different aerosol sampling instruments were ran side by side at ground level (air inlet was about 1.5 m) near the automatic air pollution (SO2, NO x, 03) and meteorological station ANAS: 1. Low pressure eleven-stage Berner type cascade impactor, Model LPI 25/0.015/2 with size cuts of 16, 8, 4, 2, 1, 0.50, 0.25, 0.125, 0.06, 0.03, and 0.015/.~m. Critical orifice allows flow rate of 25.6 l/rain. Aerosol particles were collected on AI foils. 2. Two-stage aerosol sampler with size cuts of 8.0 and 0.2 ~m. Average flow rate was 200 l/h, aerosol particles were collected on 25 mm Nuclepore PC membranes, two identical devices were ran in parallel. The cut off of the sampler is around 1.4/xm. 3. LBL sequential aerosol sampler with heated inlet tube. Flow rate was 40 1/min, aerosol particles were collected on 45 mm quartz fibre disks. Sampling periods were from five to twelve hours. Three measuring campaigns were performed: first one in the winter season (from Feb. 21 to Feb. 28, 1991; average temperature was slightly above zero °C, relative humidity about 60% during day and about 90% during night, no precipitation, low wind; Sample No 1-15), second one in spring (from March 18 to March 22, 1991; changeable weather with some showers in the first part, average T was about 10 °C, r.h. from 90 to 43%; Sample No 16-31), and the last one in the summer period (from July 15 to July 17, 1991; typical warm summer weather with some haze during low wind periods; Sample No 32-38).
Analysis AI foils, quartz filters and PC membranes were weighted after conditioning at room temperature by micro balance. Foils were cut to four pieces. Two were analysed for total particulate carbon (Cp) and sulphur (Sp) by combustion in oxygen followed by conductometric detection. The rest was put into eprouvette with 3 ml of deionised water and sonicated for two minutes. Anions were determined by ion chromatography. Filters were analysed for black carbon (BC) by measuring optical attenuation, and for Cp and Sp by combustion technique.
Chemical composition of aerosol size fractions
$655
RESULTS Total mass concentration Winter values ranged between 300 and 100 ~g/m 3, while spring and summer values ranged between 100 and 50 p.g/m 3. The three samplers have significant differences, e.g. filter .pa media, flow rates, temperature of devices, etc., and therefore also results differ in mass values. The most important with respect to the present analysis is the similarity in temporal distribution with high values during winter and lowest ones during s u m m e r sampling periods. The normalized values (summer = 1) for the three periods are 3.3 : 1.5 : 1.0 for LPI, 2.7 : 1.7 : 1.0 for two-stage, and 6.7 : 3.7 : 1.0 for the LBL sampler. Size fractions analysis Two-stage sampler: Typically tile majority of aerosol mass is in coarse fraction (Dp _> 1.4 /xm). When coarse mass is increased by a factor of about 2 in winter, the fine particle fraction increases by a factor of 4, which means that about half of the fine particles in winter is produced from nearby sources, which do not exist in summer. Ten-stage impactor: Typical bimodal mass distribution with peak values at stages 6 (mean aerodynamic diameter of 0.71/xm: accumulation or droplet mode) and 9 (mean diameter of particles 5.7 p,m: coarse m o d e ) was obtained for most samples. T h e r e are few samples indicating well expressed trimodal distribution, i.e. besides accumulation and coarse mode, also condensation mode (mean particle diameter about 0.2 p,m). It can also be concluded that condensation and accumulation modes are overlapping and that there exists also fourth mode (nucleation mode, particle size less than 0.1/xm), consistent with some other observations (e.g. Whitby, 1978, Puxbaum and Wopenka, 1984, Wall et al., 1988, John et al., 1990). Some examples of mass distribution for typical winter and summer aerosol sample obtained with our experiments are shown in Figs. 1 and 2.
[Sampl~
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er~ols in LjubUana
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1.40 2.80
5.70 11.30
Fig. 1. Size distribution of mass, Cp and Sp (A) and some inorganic ions (B) in a typical winter aerosol.
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Fig. 2. Size distribution of mass, Cp and Sp (A) and some inorganic ions (B) in a typical summer aerosol. On the basis of the results we can conclude that: i) fine carbon particles which is about half of the total aerosol mass may represents soot, ii) secondary aerosol particles (first of all sulphates and nitrates) can be produced by several mechanisms of gas-to-particle conversion under different conditions, and iii) secondary particles represent much higher amount relative to primary (coarse) ones. Systematical increase of coarse fraction mass with respect to fine fraction from winter to summer season and the fact that fine carbon plus sulphate represent considerable fraction of total winter mass but very little of the summer mass is direct evidence for efficient local particle formation mechanisms that take place during winter season.
REFERENCES Berner, A., G. Reischl, H. Puxbaum, H., V. Hudnik, M. Bizjak (1986). Physico-chemical haracterization of urban aerosols at Ljubljana. In: Proceedingsof Fifth Symposium Envi-
romnentalAnalytical Chemisoy;Atmospheric Chemisoy and SourceApportionment., Provo, 35-38 Bizjak, M., Benner, W.H., Hansen, A.D.A., Hreek, D., Hudnik, V. and Novakov, T (1988). Atmospheric Environment, 22, 12, 2851-2862 John, W, S.M. Wall, J.L. Ondo and W. Winklmayr (1990). Modes in the size distributions of atmospheric inorganic aerosol. Atmospheric Environment, 24A, 2349-2359. Puxbaum, H and B. Wopenka (1984). Chemical composition of nucleation and accumulation mode particles collected in Vienna, Austria. Atmospheric Environrnent, 18, 573-580 Wall, S.M., W.John and J.L. Ondo (1988). Measurement of aerosol size distributions for nitrate and major ionic species. Atmospheric Environment, 22, 1649-1656 Whitby K.T. (1978).The physical characteristic of sulfur aerosols. Atmospheric Environment, 12, 135-159.
0021-8502/91 S3.00 + 0.00 Pergamon Press pie
CHEMICAL COMPOSITION OF AEROSOL SIZE FRACTIONS IN LJUBLJANA M.Bizjak, V.Hudnik, T.Raunemaa Boris Kidri~ Institute of Chemistry, P.O.B. 30 YU-61115 Ljubljana, Slovenia University of Kuopio, Department of Environmental Sciences, P.O.B. 1627 SF-70211 Kuopio
ABSTRACT Three sampling and analysis campaigns were performed in order to investigate mass size distribution and chemical composition of typical urban aerosol particles in Ljubljana. On the basis of obtained data particle size lnodes were identified with predominant part of accumulation mode. KEYWORDS Urban atmospheric aerosols; cascade impactor; size fractions; modal distribution; chemical composition
INTRODUCTION Air pollution situation in Ljubljana, relatively developed industrial and commercial centre of Slovenia with about 300.000 inhabitants, is well known problem first of all during winter seasons due to various emission sources (e.g. individual space heating stoves using coal and traffic), orography (city is located in a valley surrounded from three sides by hills and mountains), and meteorological conditions (temperature inversions, fog and cold periods). Many air situation studies and regular measurements were performed regarding gaseous and particulate pollutants, their chemical composition and the role in formation of secondary species, first of all sulphates (e.g. Bizjak et al., 1988). Less information was obtained about aerosol fraction composition (Berner et al., 1986). In the present paper we report on investigation of the chemical composition of aerosol size fractions collected during measuring campaigns near city centre. Results obtained by three different sampling techniques are compared.
$653
$654
M. BITAAKet al.
EXPERIMENTAL PART
Sampling Observation and measuring place of Hydrometeorology Institute of the Republic of Slovenia, located north of the city centre, about 500 m away from the main and 100 m from the local roads, was chosen for field experiments. Three different aerosol sampling instruments were ran side by side at ground level (air inlet was about 1.5 m) near the automatic air pollution (SO2, NO x, 03) and meteorological station ANAS: 1. Low pressure eleven-stage Berner type cascade impactor, Model LPI 25/0.015/2 with size cuts of 16, 8, 4, 2, 1, 0.50, 0.25, 0.125, 0.06, 0.03, and 0.015/.~m. Critical orifice allows flow rate of 25.6 l/rain. Aerosol particles were collected on AI foils. 2. Two-stage aerosol sampler with size cuts of 8.0 and 0.2 ~m. Average flow rate was 200 l/h, aerosol particles were collected on 25 mm Nuclepore PC membranes, two identical devices were ran in parallel. The cut off of the sampler is around 1.4/xm. 3. LBL sequential aerosol sampler with heated inlet tube. Flow rate was 40 1/min, aerosol particles were collected on 45 mm quartz fibre disks. Sampling periods were from five to twelve hours. Three measuring campaigns were performed: first one in the winter season (from Feb. 21 to Feb. 28, 1991; average temperature was slightly above zero °C, relative humidity about 60% during day and about 90% during night, no precipitation, low wind; Sample No 1-15), second one in spring (from March 18 to March 22, 1991; changeable weather with some showers in the first part, average T was about 10 °C, r.h. from 90 to 43%; Sample No 16-31), and the last one in the summer period (from July 15 to July 17, 1991; typical warm summer weather with some haze during low wind periods; Sample No 32-38).
Analysis AI foils, quartz filters and PC membranes were weighted after conditioning at room temperature by micro balance. Foils were cut to four pieces. Two were analysed for total particulate carbon (Cp) and sulphur (Sp) by combustion in oxygen followed by conductometric detection. The rest was put into eprouvette with 3 ml of deionised water and sonicated for two minutes. Anions were determined by ion chromatography. Filters were analysed for black carbon (BC) by measuring optical attenuation, and for Cp and Sp by combustion technique.
Chemical composition of aerosol size fractions
$655
RESULTS Total mass concentration Winter values ranged between 300 and 100 ~g/m 3, while spring and summer values ranged between 100 and 50 p.g/m 3. The three samplers have significant differences, e.g. filter .pa media, flow rates, temperature of devices, etc., and therefore also results differ in mass values. The most important with respect to the present analysis is the similarity in temporal distribution with high values during winter and lowest ones during s u m m e r sampling periods. The normalized values (summer = 1) for the three periods are 3.3 : 1.5 : 1.0 for LPI, 2.7 : 1.7 : 1.0 for two-stage, and 6.7 : 3.7 : 1.0 for the LBL sampler. Size fractions analysis Two-stage sampler: Typically tile majority of aerosol mass is in coarse fraction (Dp _> 1.4 /xm). When coarse mass is increased by a factor of about 2 in winter, the fine particle fraction increases by a factor of 4, which means that about half of the fine particles in winter is produced from nearby sources, which do not exist in summer. Ten-stage impactor: Typical bimodal mass distribution with peak values at stages 6 (mean aerodynamic diameter of 0.71/xm: accumulation or droplet mode) and 9 (mean diameter of particles 5.7 p,m: coarse m o d e ) was obtained for most samples. T h e r e are few samples indicating well expressed trimodal distribution, i.e. besides accumulation and coarse mode, also condensation mode (mean particle diameter about 0.2 p,m). It can also be concluded that condensation and accumulation modes are overlapping and that there exists also fourth mode (nucleation mode, particle size less than 0.1/xm), consistent with some other observations (e.g. Whitby, 1978, Puxbaum and Wopenka, 1984, Wall et al., 1988, John et al., 1990). Some examples of mass distribution for typical winter and summer aerosol sample obtained with our experiments are shown in Figs. 1 and 2.
[Sampl~
Aer~ols in LjubUarm
er~ols in LjubUana
']1
N(z [.Pit, Feb 21 1991. 0957-1.906,,~
U I
0.02 0.04 0.00
0.18
0.3,5
0.71
DEe (pro)
1.40
2.60
5.70
11.30
0.02 0.04 0.09
0.18
0.35 0.71 ~1~ (11111)
1.40 2.80
5.70 11.30
Fig. 1. Size distribution of mass, Cp and Sp (A) and some inorganic ions (B) in a typical winter aerosol.
$656
M. BIZJAK
et al.
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Aerosols in l,jubljana July 15 9L. tsJB-2oxa|
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1.40 280
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0
o.o:,
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0.00
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0.35 8.?1 oo,e (pro)
J.,m
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5.70
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Fig. 2. Size distribution of mass, Cp and Sp (A) and some inorganic ions (B) in a typical summer aerosol. On the basis of the results we can conclude that: i) fine carbon particles which is about half of the total aerosol mass may represents soot, ii) secondary aerosol particles (first of all sulphates and nitrates) can be produced by several mechanisms of gas-to-particle conversion under different conditions, and iii) secondary particles represent much higher amount relative to primary (coarse) ones. Systematical increase of coarse fraction mass with respect to fine fraction from winter to summer season and the fact that fine carbon plus sulphate represent considerable fraction of total winter mass but very little of the summer mass is direct evidence for efficient local particle formation mechanisms that take place during winter season.
REFERENCES Berner, A., G. Reischl, H. Puxbaum, H., V. Hudnik, M. Bizjak (1986). Physico-chemical haracterization of urban aerosols at Ljubljana. In: Proceedingsof Fifth Symposium Envi-
romnentalAnalytical Chemisoy;Atmospheric Chemisoy and SourceApportionment., Provo, 35-38 Bizjak, M., Benner, W.H., Hansen, A.D.A., Hreek, D., Hudnik, V. and Novakov, T (1988). Atmospheric Environment, 22, 12, 2851-2862 John, W, S.M. Wall, J.L. Ondo and W. Winklmayr (1990). Modes in the size distributions of atmospheric inorganic aerosol. Atmospheric Environment, 24A, 2349-2359. Puxbaum, H and B. Wopenka (1984). Chemical composition of nucleation and accumulation mode particles collected in Vienna, Austria. Atmospheric Environrnent, 18, 573-580 Wall, S.M., W.John and J.L. Ondo (1988). Measurement of aerosol size distributions for nitrate and major ionic species. Atmospheric Environment, 22, 1649-1656 Whitby K.T. (1978).The physical characteristic of sulfur aerosols. Atmospheric Environment, 12, 135-159.