Sources and physico-chemical characteristics of the atmospheric aerosol in Southern Norway

Pergamon

Armospheric Enwonment Vol. 30, No. 9, pp. 1391 1405, 1996 Copyright Q 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 1352-2310196 fl5.00 + 000

1352-2310(95)00460-2

SOURCES AND PHYSICO-CHEMICAL CHARACTERISTICS OF THE ATMOSPHERIC AEROSOL IN SOUTHERN NORWAY TUOMO

A. PAKKANEN,*

RISTO E. HILLAMO

and PETRI KER0NEN-f

Finnish Meteorological Institute, Air Quality Department, Sahaajankatu 20 E, FIN-00810 Helsinki, Finland

WILLY MAENHAUT

and GEERT DUCASTEL

University of Ghent, Institute for Nuclear Sciences, Proeftuinstraat

86, B-9000 Ghent, Belgium

and JOZEF M. PACYNA Norwegian Institute for Air Research, P.O. Box 100, N-2007 Kjeller, Norway (First receioed 3 April 1995 and injinalform

3 November 1995)

Abstract-An intensive aerosol sampling campaign was carried out simultaneously at Birkenes and Nordmoen, southern Norway, from 11 April to 4 May 1988. Two different size segregative sampling instruments were used at each site. Parallel analysis was performed using several methods which allowed the determination of up to 45 components. The atmospheric concentrations were mostly found to be similar at the two sampling sites, which are separated by a distance of about 250 km. During long-range transport episodes, the pollutant concentrations were 20-50 times higher than during background periods. At the Birkenes site detailed information about the elemental and particle mass size distributions was obtained from Berner low-pressure impactor samples. The aerosol fine particle mode clearly shifted to larger particle sizes when the average relative humidity was higher than 80% during sampling. The average fine to total elemental concentration ratios of most elements were found to be similar for the different samplers and for the two sites, although differences between the sites occurred depending on the origin of the air masses sampled. A new approach based on the size distributions measured, the relative size distributions (RSD) method, was developed for the assessment of local and regional aerosol sources. The RSD method and conventional methods revealed local/regional sources of Mn, Zn, Pb, Bi, Br, I, Si and K. The interelemental concentration ratios in air masses of different geographical origin were studied and found to be similar in this study and in southern Sweden (Swietlicki et a/., 1989) for air masses originating from the U.K. Key word index: Atmosphere, aerosol, elements, elemental ratios, sources of aerosols, impactors, size distributions.

1. INTRODUCTION

Since the 198Os,long-range transport (LRT) of pollutants has been studied intensively at various receptor sites in southern Scandinavia (Lannefors et al., 1980, 1983; Martinsson et al., 1984; oblad and Selin, 1986; Amundsen et al., 1987, 1992; Swietlicki et al., 1989; Cornille et al., 1990). Even though in some of these studies a limited number of components were measured and/or the aerosol size fractions collected were inaccurately defined, it was clear that the highest pollution levels were associated with air masses ori-

*To whom correspondence should be addressed. t Present address: University of Helsinki, Department of Physics, P.O. Box 9, FIN-00014 University of Helsinki, Finland.

ginating from the British Isles and eastern and central Europe. LRT models for sulphur (OECD, 1979; Eliassen and Saltbones, 1983) and trace elements (Pacyna et al., 1984, 1989) have been developed to study the links between the distant European source areas and the receptor sites in Scandinavia. Rahn and Lowenthal (1984) proposed regional signatures for atmospheric aerosols in the eastern U.S. and, in a similar manner, Swietlicki et al. (1989) determined elemental sector signatures for air masses coming to southern Sweden. This paper presents the results from an intensive 23 d atmospheric aerosol sampling campaign conducted during spring, 1988, in southern Norway. Compared to earlier published data from southern Norway this study presents data for a larger number of components sampled simultaneously at two sites

1391

1392

T. A. PAKKANEN

with more accurate particle size determination and/or more detailed size fractionation, and measured by a wide variety of analytical techniques. Preliminary results for the ionic species and comparisons of parallel measurements were presented by Hillamo et al. (1992) and Maenhaut et III. (1993), respectively.

2. EXPERIMENTAL

2.1. Aerosol sampling

The aerosol sampling was performed at two locations in southern Norway, i.e. at Birkenes and Nordmoen, during the period from 11 April to 4 May 1988. Birkenes is a rural site situated close to the southernmost tip of Norway. Nordmoen is located 40 km to the north of Oslo and is occasionally influenced by the atmospheric emissions from sources in the Oslo region. The location of the sampling sites and some important regional point sources are shown in Fig. 1. In Birkenes the sampling instrumentation was as follows: 24 h measurements using a stacked filter unit (SFU), 48 or 72 h measurements using Berner low-pressure impactors (LPIs) and continuous measurements using an electrical aerosol analyser (TSI model 3030). At the Nordmoen site an SFU sampled for 24 h periods, a filter sampler with three pre-impactor stages (ILVS) sampled for 24 h periods in parallel with the SFU and a condensation nucleus counter (TSI model 3020) measured continuously. Details about the SFU

rf al

sampling method are described by Cahill er ul. (1977), Heidam (1981) and John et ul. (1983). The SFU sample collection started at about 8:00 local time in Birkenes and at about 16:OOlocal time in Nordmoen. The SFUs were collected on two 47 mm diameter Nuclepore polycarbonate filters: an 8.0 itrn pore size prefilter and a 0.2 pm pore size back-up filter. The 50% cut-off diameter of the prefilter was about 2pm equivalent aerodynamic diameter (EAD). At Birkenes there was no sampling on the last day of the campaign (34 May). The collection of samples 15 and 20 at Nordmoen and of sample 13 at Birkenes failed, and, as a result, the total number of valid SFU samples is 21 for both sampling sites. The air flow rate through the SFUs was about 7 G min-’ (corresponding total air volume: 10 m3) for the first seven Birkenes samples and the first six Nordmoen samples, but was increased to about 12 Cmin-’ (total air volume: 17 m3) for the remaining samples. This increase in the air flow rate causes some decrease in the 50”/0 cut-off diameter of the prefilter (John er al., 1983). However, it seemed to have only a minor effect on the data obtained, since, for example, the fine to total ratio for S remained virtually unchanged. At Birkenes, the Berner low-pressure impactor (LPI) designed by Berner (Berner, 1984; Berner and Liirzer, 1980) collected samples on poreless Nuclepore polycarbonate film. The substrates collecting coarse particles (EAD > 2 pm) were greased with Apiezon L vacuum grease (Hiliamo and Kauppinen, 1991). The air volume sampled was about 70 m3 for the 48 h samples and 100 m3 for the 72 h samples. The 50% cut-off diameters of the 10 impactor stages at the nominal flow rate of 25 (rnin-’ were 8.0, 4.0, 2.0, 1.0, 0.57, 0.35, 0.17, 0.092, 0.064 and 0.034 pm EAD for stages 10-l. and the 50% cut-off diameter of the pre-stage was 16 pm EAD. The values for the compressible flow stages (stages 61: cut-offs 0.57~.034~m EAD) were calibrated experimentally by Hillamo and Kauppinen (1991). In Birkenes the LPI samples l-9 correspond to parallel SFU samples l&2,3-4, 5-7, 8-9, 10-l I, 12-14, 15-16, 17-18 and 19--21, respectively. At Nordmoen, a so-called impactor low volume sampler (ILVS) was utilized to collect samples in parallel with the SFU. This ILVS contains a 0.4 pm pore size Nuclepore filter, which is preceded by three impaction stages with 50% cutoff points of 10,6 and 2 pm EAD, and the device is operated at a flow rate of 15 P min I. More details about the ILVS are given by Hillamo et al. (1992). 2.2. Analysis

MI, F&in 0

+

NCRDMOEN

Gravimetric, ion chromatograph (IC) and inductively coupled plasma mass spectrometry (ICP-MS) analyses were performed at the Norwegian Institute for Air Research in Norway, and particle-induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA) measurements were carried out at the Institute for Nuclear Sciences, University of Ghent, Belgium. While with PIXE and INAA a nondestructive instrumental analysis was carried out (Schutyser et al., 1978; Maenhaut et al., 1981; Maenhaut and Raemdonck, 1984), the ICP-MS analysis involved an acid dissolution step with 0.2 M nitric acid (Pakkanen et al., 1993) prior to analysis. The ICP-MS measurements were carried out with a VG Plasmaquad instrument using an ordinary scan procedure. However, as the dissolution of the samples for ICP-MS was somewhat inefficient for certain elements, the ICP-MS data were used only to complement the other methods with results for Mg, Rb, MO, Ba and Bi and partly for Cu and Cd.

3. RESULTS AND DISCUSSION

3.1. SFUjne

Fig. 1. The sampling sites, Birkenes and Nordmoen, and some regional aerosol sources.

particle mass and elemental concentrations

The median concentrations and the 25 and 75 percentile concentrations of selected components in the

The atmospheric aerosol in southern Norway

1393

Table 1. The 25, 50 and 75 percentiles of the aerosol mass and elemental concentrations in the fine fraction of SFU samples at Birkenes and Nordmoen (ILVS samples for Mg, Cu, ,Rb, MO, Cd, Ba, Bi, SO& Element

Na Mg Al Si S Cl K Ca SC Ti V Cr Mn Fe co Ni CU Zn Ga As Se Br Rb MO Cd In Sb

cs Ba La Sm W AU Pb Bi Mass so,-s NOx-N NH,-N

NO3-N

and NH,-N

Birkenes 25

75

39

50 10 13 45 371 < 60 24 13 < 0.02 < 2.1 0.56 < 2.7 2.2 13 < 0.3 < 0.63 < 0.6 5.9 < 0.2 0.33 < 0.4 2.6 4 0.4 0.13 < 0.9 < 0.008 0.25 1.8 0.17 0.26 < 0.03 < 0.005 < 0.08 0.0022 3.6 0.038 4.5 340 14 250

10 < 29 261 < 47 15 8 < 0.02 < 1.0 0.26 < 2.2 1.2 < 0.2 < 0.5 < 0.5 2.6 < 0.2 0.21 < 0.3 1.7 < 0.4 0.09 < 0.8 < 0.007 0.09 1.4 0.13 0.16 < 0.03 < 0.003 < 0.06 0.0019 1.8 0.020 3.1 95

Aerosol mass concentration DL: detection limit. --: no data.

Nordmoen 75

25

125 49 35 74 1210 < 79 45 17 < 0.03 2.1 2.3 < 3.8 3.9 24 < 0.3 0.63 0.81 9.5 < 0.5 0.62 < 0.5 4.3 0.61 0.28 < 1.2 < 0.013 0.43 2.7 0.23 0.61 0.03 1 0.005 0.08 0.0028 7.0 0.082 12.6 1170 33 650

31 2.7 18 50 194 < 15 27 13 < 0.008 < 1.2 0.14 < 2.3 0.8 11 < 0.12 < 0.5 < 0.4 4.1 < 0.1 0.14 < 0.4 1.3
in pg mm3 and other concentrations

Birkenes and Nordmoen SFU fine ( < 2 pm EAD) particle samples are presented in Table 1. For most elements the concentrations were similar at the two sampling sites, with the differences being largest for K, V, Mn, Zn, I, Pb, and for the crustal elements Al, Si and Fe. The median values for most components in Table 1 are similar to those reported in previous aerosol studies for southern Scandinavia (Lannefors et al., 1980, 1983; Martinsson et al., 1984; t)blad and Selin, 1987; Amundsen et al., 1987, 1992; Swietlicki et al., 1989; Cornille et al., 1990). This suggests that the atmospheric particulate elemental concentrations did not exhibit drastic changes over the past decade. At Nordmoen, very good agreement was observed between the fine particle filter data from the parallel SFU and ILVS samples, but the agreement for the

AE 30:9-c

at Nordmoen)

50

75

64 5.7 23 65 264 20 45 15 < 0.008 1.6 0.37 < 2.9 1.4 26 < 0.12 < 0.5 0.46 13 < 0.2 0.31 < 0.4 2.2 0.22 0.02 0.06 < 0.005 0.23 1.1 0.10 0.20 0.04 < 0.004 < 0.07 < 0.002 9.3 < 0.002 4.7 250

84 9.5 41 123 1318 27 72 23 0.008 2.7 1.7 < 3.9 3.0 35 0.12 < 0.8 0.82 20 < 0.3 0.74 < 0.5 4.7 0.42 0.18 0.29 < 0.007 0.55 2.0 0.13 0.56 0.04 0.005
110

1240

in ngm-3

coarse particle fraction was not as good (Maenhaut et 1993). The daily concentration variation (time trend) of nine typical anthropogenic elements in the Birkenes and Nordmoen SFU fine particle samples is presented in Fig. 2. This figure shows that the concentrations were elevated for samples 4,s and 6 (episode I) and for samples 16-23 (episode II). The air mass back trajectories (provided by the Norwegian Meteorological Institute, Oslo) showed that the air masses were coming from the British Isles during episode I, but for episode II the back trajectories moved slowly from NE to SW, indicating that most of the sampled material had a mixed origin. The time trends for the fine particle mass and various elements were generally fairly parallel at Birkenes and Nordmoen. As these

al.,

The atmospheric

aerosol

mean mass fractions), presented earlier by Maenhaut et al. (1993), indicated three groups: 1. Elements with most of their mass in fine ( < 2 pm EAD) particles: S, V, Zn, As, Br, Sb, I, Pb. 2. Elements with roughly equal amounts of their mass in fine and coarse particles: K, Mn, Cu, (MO, Cs, W). 3. Elements with most of their mass in coarse partitles: Na, Mg, Al, Si, Cl, Ca, SC, Ti, Fe, La, Sm. All elements from group 1 are known to be emitted in large quantities by various anthropogenic hightemperature sources, but S, Br and I have also large

in southern

1.195

Norway

natural (i.e. marine) sources. The group 2 elements, Cu, K and Mn have anthropogenic fine particle sources and dispersal of mineral dust is a natural coarse particle source for these elements. In group 2 there are also MO, Cs and W which are in parentheses because the concentrations of these elements were close to or below the detection limits, and therefore the uncertainty in their size distributions is large. The elements of group 3 are mainly of coarse particle crustal and/or marine origin. Table 2 presents the average concentration percentage from total and average mass median aerodynamic

Table 2. Average mass median aerodynamic diameters (MMADs in pm) and average concentration percentage from total (cont. %) and associated standard deviations (SD.) for the largest fine and coarse particle modes as obtained by lognormal curve fitting to the inverted LPI data Element

S

MMAD

SD.

0.419 2.95

* 0.034 + 0.12

C61 Ccl

0.354 4.92

k 0.063 * I.21

0.32 I 5.39

k 0.061 f 0.72

f c sum

I.11 5.57

f

1.16 5.61

f C

[#]

f C

V

f C

Mll

Fe

C

k 10 + 10

161 [61

0.838 3.94

* 0.081 f 1.50

82 4 X6

161 161

32 59 91

?I 18 IL 26

Dl C31

0.915 5.08

+ 0.166 + 0.83

41 43 91)

c51 c51

56 26 82

+ 11 If 11

[51 I51

0.714 4.13

) 0.161 f 0.03

50 I6 66

k 0.25 * 0.37

51 43 94

Ii 7 +9

I51 I51

I .07 4.50

i_ 0.43 + 0.71

41 49 90

i 0.34 * I.14

14 81 95

+ 5 + 7

C61 C61

0.808 4.98

+ 0.283 _+ 1.04

20 79 99

0.851 5.02

+ 0.300 + 1.52

41 55 96

1.21 4.34

+ 0.24 ri: 1.37

51 29 80

* * *

0.955 4.52

+ 0.136 4 0.22

63 12 75

sum CU

f C

sum Zn

[51 C61

0.333 4.00

k 0.086 i 0.81

0.297 4.97

+ 0.042 f 0.71

C61 II51

39 23 62

0.724 3.87

i: 0.109 & 0.04

69 17 86

f c sum

0.390 2.24

+ 0.024 + 0.29

[51 [41

66 15 81

0.726 4.13

* 0.144 0.10

60 9 69

f c

0.324 3.56

_t 0.083 * I.13

c51 M

70 15 85

0.650 3.47

& 0.293 * 1.40

73 20 93

f C

sum f C

sum I

Pb

I51 C51

* 0.210 + 1.11

sum

Sb

* 15 iz 6

0.597 4.55

f C

As

cont.

86 10 96

sum

%

S.D.

[#]

sum

cont.

MMAD

SD.

sum K

LPI samples 3 and 9 (LRT samples) average RH = 80 and 85%

LPI samples 2, 4, 5, 6, 7 and 8 average RH = 47-75%

65 I5 80

+ 21 * 2

M r41

%

S.D.

Results are given separately for the LRT-episodes (LPI samples 3 and 9; average relative humidities 80 and 85%) and for LPI samples 2,4, 5,6,7 and 8 (average relative humidities 47-75%). Instead of S.D.s the arithmetic difference is presented for the two LRT samples. The number of inspected samples is in brackets. # : number of samples. f: largest fine particle (EAD i 2 pm) mode. c: largest coarse particle (EAD > 2 pm) mode. sum: sum of largest fine and largest coarse mode for percentage from total concentration. -: no data. *: concentrations could not be well calculated from the data inversion.

1396

T. A. PAKKANEN

diameters (MMADs) with the corresponding standard deviations or arithmetic differences for the largest fine particle mode and for the largest coarse particle mode as obtained by lognormal curve fitting (Winklmayr et al., 1990) of the MICRON inverted LPI data. All the elements examined had one or two modes for the fine (EAD < 2 pm) and one or two modes for the coarse (EAD > 2 pm) size fractions. Sometimes, there was a minor mode with a centre at about 0.08 pm EAD, but probably this mode was in most cases the result of coarse particle bounce-off. Support for such an explanation was provided by the fact that the elemental ratios to aluminium in that very fine mode were rather similar to the ratios in the particle fraction larger than 4 pm EAD. In certain cases (see Sections 3.4 and 3.5), however, this very fine mode appeared to have been created by local and/or regional sources. As an example, MICRON inverted (Wolfenbarger and Seinfeld, 1990, 1991) size distributions for selected elements in the LPI sample 9 (representing part of the LRT episode II) are given in Fig. 3a and b. Figure 3c and d shows size distributions of selected elements for LPI sample 2, which represents a situation of a rather low concentration of pollu-

et al.

tant elements. The LPI sample 2 exhibited a high sodium concentration and clearly represented air from marine origin. Table 2 further indicates that in spite of the number of modes (normally 3 or 4) the sum of the largest fine particle mode and the largest coarse particle mode usually accounted for more than 80% from the total concentration. Exceptions are V, As and I for the LRT samples and Sb for all samples. In accordance with the results of Tang et al. (1978) higher average relative humidities (80 and 85% for the LRT samples vs 47-75% for the rest of the samples) resulted in higher fine particle MMADs (see Table 2). However, it is not known if, and to what extent, the much higher concentrations in the LRT samples (Fig. 2) may have increased the fine particle MMADs for these samples. 3.3. Fine to total elemental concentration ratios in the SFU and LPI samples The average values for the fine to total aerosol concentration ratios of selected elements in the Birkenes LPI and SFU samples and in the Nordmoen SFU samples are given in Table 3. For the anthropogenic elements (group 1 in Section 3.2) the SFU ratios were

b

3G

. __---

25

1.6

20

.Ol

/_Ii M"

/

0.1

Particle

Diamleter,

j_G

Particle

Diameter,

&I

Particle

Diameter,

pm

3.0 2.5 2.0

-

1.5 1.0 -

Particle

Diameter,

pm

Fig. 3. Size distribution of selected elements for LPI samples 9 (a and b) and 2 (c and d). The left-hand and the right-hand legends correspond to the left-hand and the right-hand concentration scales, respectively. Inversion code MICRON (Wolfenbarger and Seinfeld, 1990,199l) was used for deriving the curves from the raw data.

The atmospheric aerosol in southern Norway

1397

Table 3. Average fine to total concentration ratios and associated standard deviations for the Birkenes LPI and SFU samples and for the Nordmoen SFU samples (the number of samples is indicated in brackets) Birkenes Element Na Mg Al Si s Cl K Ca SC Ti V Mn Fe co Ni cu Zn Ga As Se Br MO In Sb I cs La Sm EU W Au Pb Mass

LPI x+s[N] 0.29 f 0.24 f 0.26 f 0.30 + 0.88 k 0.52 * 0.48 + 0.14 + 0.16 k 0.15 f 0.77 f 0.51 k 0.28 f 0.52 f 0.91 * 0.42 f. 0.77 f 0.80 f 0.85 + 0.76 + 0.87 + 0.66 + 0.93 k 0.77 f 0.90 f 0.75 + 0.26 f 0.18 f 0.67 + 0.70 + 0.67 + 0.90 * 0.77 *

0.11 0.11 0.10 0.27 0.05 0.34 0.12 0.04 0.05 0.04 0.09 0.08 0.09 0.30 0.21 0.14 0.06 0.39 0.06 0.19 0.15 0.20 0.18 0.13 0.09 0.17 0.13 0.07 0.16 0.17 0.28 0.07 0.12

Nordmoen SFU I f s [N]

[S] [6] [S] [8] [8] [8] [S] [8] [6] [6] [S] [S] [8] [5] [S] [4] [S] [6] [S] [S] [8] [7] [6] [S] [S] [4] [6] [S] [S] [7] [S] [8] [7]

0.37 + 0.11 [21] 0.25 f 0.11 [21] 0.31 + 0.23 [15] 0.84 k 0.07 [20] 0.48 k 0.13 [20] 0.22 + 0.10 [16] 0.21 k 0.08 0.71 +0.11 0.51 f 0.08 0.30 * 0.13 0.58 f 0.10

[S] [20] [20] [21] [l l]

SFU x+s[N] 0.39 * 0.37 + 0.16 + 0.20 f 0.87 + 0.56 f 0.48 f 0.20 + 0.18 f 0.17 k 0.55 + 0.33 * 0.24 + 0.44 +

0.10 0.08 0.04 0.10 0.07 0.18 0.10 0.07 0.04 0.08 0.19 0.10 0.07 0.06

[21] [3] [21] [21] [21] [9] [21] [21] [7] [12] [21] [21] [21] [lo]

0.41 f 0.14 [7] 0.71 + 0.13 [18]

0.71 + 0.28 [9] 0.74 * 0.10 [21]

0.85 5 0.12 [17]

0.73 k 0.18 [17]

0.79 f 0.88 k 0.74 + 0.28 k 0.23 + 0.55 * 0.53 * 0.25 + 0.77 f

0.15 0.04 0.06 0.11 0.08 0.07 0.11 0.12 0.05

[17] [16] [S] [S] [S] [S] [ll] [6] [lo]

0.50 f 0.81 f 0.89 f 0.66 * 0.26 k 0.17 + 0.47 + 0.43 +

0.09 0.08 0.05 0.05 0.10 0.05 0.07 0.07

[3] [14] [15] [7] [20] [15] [7] [14]

0.78 k 0.07 [14] 0.71 + 0.13 [231a

Note: the fine to total ratios for the LPI samples were defined as the ratio of the particulate or elemental mass in the fine fraction (sum of stage l-7) to the total particulate or elemental mass (sum of stages l-10). a From ILVS data.

similar at both sampling sites with only arsenic and vanadium having slightly lower ratios in Nordmoen. The lower ratio for V in Nordmoen was likely due to higher concentrations of coarse particle mineral dust at Nordmoen, which also explains the differences found for Al, Si, Mn and Fe. Ratios for Cu were lower in Birkenes which may mean that near Nordmoen there were local and/or regional fine particle Cu sources. The average fine to total concentration ratios of elements in Birkenes were normally similar for the SFU and the LPI, the difference being greatest for Ca and Au. The Au concentrations were low, which resulted in large errors in the analysis and probably caused the large SFU-LPI difference. 3.4. Local and regional sources of particulate trace elements Mn. The concentration of fine particle Mn at Birkenes is high in samples 3,8 and 14. These elevated

Mn concentrations are found in air masses coming from north and/or northwest of Birkenes which is in accordance with the observations of Cornille et al. (1990). The probable origin of this manganese is the regional Mn and Fe industries (see Fig. 1). Also, SFU sample 4 in Nordmoen has a high Mn concentration and the back trajectories suggest that this Mn came from the same Mn source region as mentioned above. Zn, Pb and Bi. Compared to Birkenes, fine particle zinc and lead concentrations are 3-9 times higher in Nordmoen for samples 1, 2, 3, 4, 9, 17 and 18, which indicates that local and/or regional Pb and Zn sources affected the Nordmoen measurements. The Nordmoen to Birkenes ratios for fine and coarse particle Zn, Pb, Al and Fe generally followed each other for samples 1, 2, 3, 4 and 9. Since coarse particle profiles for Al and Fe are indicative of mineral dust or other crustal material, it is probable that part of the additional Zn and Pb in Nordmoen comes from

1398

T. A. PAKKANEN

contaminated local soil or more likely road dust. Another fact supporting this assumption is that the fine to total aerosol ratios of Al and Fe were rather low for the above samples, which indicates that there was not much coal fly ash present. Pacyna et al. (1989) also found local zinc in Nordmoen, but assumed that two municipal incinerators near Oslo were responsible. According to the back trajectories, it is likely that these incinerators are responsible for the observed Zn and Pb in samples 17 and 18. Samples 17 and 18 were the only samples for which the measured fine particle Bi concentrations were higher in Nordmoen compared to those in Birkenes. Thus, some Bi sources and Zn and Pb sources seem to exist in the same direction from Nordmoen, e.g. northeast-southeast (see also Section 3.6.1). Br and I. The median SFU fine particle Nordmoen to Birkenes concentration ratios are 0.84 and 0.62 for Br and I, respectively, which indicates that these elements are somewhat more abundant at the coastal Birkenes site. The parallel LPI and SFU measurements in Birkenes were compared by Maenhaut et al. (1993) and the average LPI to SFU ratios for fine particle Br and I were 0.89 and 0.48, respectively. Collection of gaseous compounds on filters except those made of Teflon (Harrison and Sturges, 1983) and evaporation from filters (Sturges and Harrison, 1986) can be expected for Br. Nevertheless, the results for Br showed rather good agreement between the LPI and SFU. Separate collections were not made for gaseous species and it is not known to what extent vapour-phase Br was present. The average LPI to SFU ratios, as presented by Maenhaut et al. (1993), were close to unity for most elements, but I showed a low value of 0.48. Large amounts of gaseous Br and I are known to evolve from the sea in springtime (Sturges and Harrison, 1986; Sturges, 1990). A possible explanation for the low ratio of I is that during the campaign there was gaseous I present in Birkenes and that the SFU Nuclepore filters and/or the particulate material on the filters collected gaseous I, but the LPI sampler did not. Another possible explanation is that part of the collected particulate I evaporated from the LPI impaction samples. However, more efficient evaporation can possibly be expected from the filter samples than from the LPI, as has been observed for nitrate when Teflon filters are used (John et al., 1988). Si. Silicon is present in extremely high concentrations as fine particles for SFU samples 6 and 7 from Birkenes. The Si size distribution for the corresponding LPI sample (LPI-3) is totally different from those of the other LPI samples (see Fig. 1 in Maenhaut et al., 1993). This fine particle Si most likely originates from silicon and SIC industries in southern Norway (Cornille et al., 1990; see also Fig. 1). K. Potassium was sometimes present in high concentrations in the fine particle mode. Contributions from crustal rock, using Al as reference (Mason, 1966), and from sea spray (reference element Na) were sub-

et al.

tracted from the total fine particle K and thus fine K, originating from sources other than the above mentioned, was obtained. In Birkenes and Nordmoen the mean percentage of this additional fine K for SFU samples l-9 was 43 and 70%, respectively, and the percentage ranges were O-82% and 38893%, respectively. Coal fly ash is not expected to be responsible for this additional K since K and Al have a similar ratio in crustal rock and fine particle coal fly ash (Kauppinen and Pakkanen, 1990). Most of this additional K likely originated from biomass burning (Stevens, 1985; Calloway et. al., 1989) and/or from incinerators (Dzubay et al.. 1988). 3.5. Relative size distributions ,for estimating aerosol sources

method (RSD method)

Elemental ratios to aluminium and to sodium are used for the evaluation of elemental enrichment factors with respect to crustal rock and sea salt, respectively. These enrichment factors are useful for bulk samples or for the coarse particle size fraction since atmospheric aluminium and sodium are mainly associated with coarse particles. These two elements can be in relatively low concentrations in fine particles, which increases the uncertainty in the analysis of these elements in fine aerosol fractions. Moreover, the fine particle aluminium and sodium may no more originate from crustal dust and sea, but from other sources (e.g. combustion processes). Compared to the above enrichment factors the RSD method is more useful when fine particles and aerosol sources are studied. The RSD curves for LPI samples are calculated as follows: (a) the concentration of element E in stage 5 (0.35-0.57 pm EAD) is multiplied by a factor that makes this concentration equal to the concentration of a reference element in stage 5, (b) the concentrations of E in the other stages are multiplied by the same factor, (c) the ratios of the obtained normalized concentrations of E to the reference element concentrations are calculated for each stage (the ratio is 1 for stage 5). In other words: (i) the concentrations of element E in all the LPI stages are multiplied by a factor that makes the concentrations of E and the reference element in stage 5 equal, and (ii) ratios of the normalized E concentrations to reference element concentrations are calculated for each stage. Stage 5 (50% cutoff = 0.37 pm EAD) was selected as the normalization point because the concentrations of pollutant elements are high for this stage and the relative analysis errors are at their minimum. Sulphur was selected as the reference element since (i) sulphur was usually present as measurable concentrations in all LPI stages, and (ii) the shape of the sulphur size distributions (see Fig. 3a and d) is such that the RSD values obtained are usually higher than one. However, depending on the sampling site and analysis methods

1399

The atmospheric aerosol in southern Norway available, some other element may be more useful as reference. Figure 4a-c shows RSD values for selected elements with S as reference element ( = RSD(S) values). Figure 4a represents the LRT episode I where the air masses came from the British Isles (LPI sample 3) and Fig. 4b represents LRT episode II with air coming from central Europe (LPI sample 9). Figure 4c (LPI sample 2) describes a situation where local sources of certain elements affected strongly the RSD(S) curves of these elements. To verify the influence of local sources to the RSD(S) curves the normalized Pb to sulphur ratio curves (nPb/S curves) were calculated for three different LPI samples collected in June 1987 in the centre of Helsinki, capital of Finland. These nPb/S curves, presented in Fig. 4d, appeared to be

nearly identical and reached values between 8 and 15 for coarse particles, which was 2-3 times higher than those obtained for Cd and V. The influence of local sources (car traffic) was even more dramatic for fine particles: for LPI stage 2 (50% cut-off = 0.069 pm) these curves showed values of 20-32 and for stage 1 (50% cut-off = 0.042 pm) the values were 120-240, which was 20-50 times higher than for the other elements measured in these LPI samples. Thus, a sign of local sources is high RSD(S) values for fine particles and slightly elevated RSD(S) values for coarse particles. In Fig. 4b Mn has very high nMn/S values of 184 and 80 for stages 1 and 2, respectively. Also, in Fig. 4a and c Mn has high nMn/S values compared to several other elements. As indicated above, high KSD(S)

11 10

F

LPI-3

4a

P

-+-

9 a

-i?-

MnlSx249

-*-

h/w4

b

As/S1003

7 I

e

6

p

5

-

4

1 0

--

SblSlWJ

v

IVSx405

d---

PblSx22.5

--+--

Ewsx331

-x-

K/k16

-

3 2

v/%202

I-

I----

0.01

0.1

1

10

100

Particle diameter, pm

30 --

4b 25

-

0.1

1

10

v/sx1495

---13-

MrVSx1280

-•-

2rVSxl42

v

As1sx2140

v-

S4sx2750

+

I/sxlwl

A-

Pb/Sxl23

-

BrlSx830

-x---

K/&59

---xc---

CUlSx3740

100

Particle dkmeter, pm

Fig. 4a and b. Selected RSD(S) curves for LPI-3 and LPI-9

T. A. PAKKANEN et al.

---w---

LPI-2

j -

Mn/SxXC

( -+-

ZnlSx230

I

0.1

1

10

v/sxaec

---+--I / -A-

Sb/SXllJa)

AslSX52Ql

I e

llSX800

--

Pb/SdlO

-

K/S%52

-x--

k/SXlW

---a---

Pb/SxlM

100

Particle diameter, urn

Fig. 4c. Selected RSD(S) curves for LPI-Z

Helsinki,summer 1987

0.1

1

10

1M)

Parttcle diameter, pm

Fig. 4d. Three nPb/S curves for samples collected in Helsinki, summer 1987.

is a sign of local sources. In Fig. 4a the curves of K and Mn follow each other closely from stage 1 to stage 9. Also, in Fig. 4b there are similarities between the nK/S and nMn/S curves, with the Mn curve being steeper at both sides. These steeper wings of the RSD(S) curve of Mn may mean that the Mn source(s) is(are) closer to the sampling site and/or is(are) stronger than the K source(s). In Fig. 4c the nK/S values of stages 1 and 2 are missing (K values were below the detection limit), but K and Mn follow each other closely for stages 3-7. It really looks like similarly to Mn also K had local fine values for fine particles

particle sources. In Fig. 4b and c I has high values for fine particles. Sturges and Harrison (1986) have shown that during springtime gaseous I compounds are released from the sea and it is possible that these I compounds are involved. The mineral dust and sea-salt elements Al, Si, Ca, Fe, Ti, Na and Cl form their own group of similar (high ratios for coarse particles) RSD(S) curves, but these elements, being mostly of natural origin, are not discussed here. Cu, K and Mn have rather high values for coarse particles because of the contribution from mineral dust and/or crustal material. Mineral dust

The atmospheric aerosol in southern

Norway

1401

Table 4. Grouping of elements with similar RSD(S) values for fine and coarse particles Group

BLPI-3

BLPI-9

BLPI-2

Fine particles

Fl F2 F3 F4

As, Br, I, Pb, S, Sb, V, Zn K, Mn

As, Br, I, K, Sb, V

I, Pb, S, V As, Br, Sb

As, Br. I, Pb, S. Sb, V Zn

s. v As, I

Cu, K, Mn, Zn

Cu, K, Mn

Sb K Mn, Zn

S (Fe) Pb, Zn (Cu) Mn

I, K, Sb S Mn (As, V)

Coarse particles

Cl c2

c3 c4 c5

also contains V, which is reflected in the slightly elevated nV/S values in Fig. 4b. The nZn/S curves have a special (typical?) shape in Fig. 4a and c and also LPI samples 5 and 7 and to some extent also LPI sample 4 showed similar nZn/S curves. Often the nZn/S curves were clearly different from the other RSD(S) curves which might be an indication of different sources (probably local and/or regional sources as discussed in Section 3.4). In Fig. 4c (LPI sample 2) for stage 9, Sb has a value of 12, which is high compared to the other pollutant elements. Moreover, for stages 1 and 2 Sb shows high nSb/S values of 38 and 15, respectively, which were the highest nSb/S values during this campaign. Elements with similar RSD(S) curves for fine (stages 61) and coarse (stages 10-7) particles are grouped in Table 4. Although the RSD(S) curves are somewhat different in the different LPI samples, the groups of elements in Table 4 are similar for fine particles. However, occasionally, the behaviour of K, Mn, Pb, S and Zn can differ from group 1 elements. Overall, the RSD method was capable of revealing the same local and/or regional sources as discussed in Section 3.4. The reason for this special capability of the RSD method is probably based on phenomena like physical and chemical state of components, condensation rates of different gases and coagulation rates of particles of different composition and size. Meteorological parameters may also affect the RSD curves and thus make the interpretation more complicated. To give a more reliable explanation for the RSD(S) curves, a much larger number of these curves should be inspected. 3.6. Interelemental ratios 3.6.1. Interelemental ratios to excess V in southern Norway. In order to study interelemental ratios for air masses of different geographical origins, a sector division used earlier by Amundsen et al. (1992) was employed for Birkenes and is shown in Fig. 5. For Nordmoen the sectors were drawn to be as similar as possible to the Birkenes sectors. Vanadium not associated to crustal rock (excess vanadium = VX) was chosen as a reference element since no major local contribution was found for this element at the samp-

Fig. 5. Sector division

for Birkenes 1992).

(from Amundsen

rt al.,

ling sites. A drawback of using VX as a reference is the correction for crustal rock contribution which may cause additional error. Elemental to VX fine particle mass ratios and the corresponding sectors and samples are presented in Table 5. Only samples with air masses originating from one or two dominating sectors were included. The ratios presented in Table 5 are based on only a few samples and are thus preliminary. A common feature of the data in Table 5 is that the ratios are clearly higher in the air masses coming from W. NW, N or NE (sectors 8, 1 and 2). This is because major vanadium sources, such as burning of fuel oil to produce electricity and heat, are situated south of the sampling sites. The contribution of local sources of K, Zn and Pb in Nordmoen is obvious when the ratios for sectors 8 + 1 and 1 + 2 are compared between the two sites. At each site, sectors 5 and 6 had similar ratios, the difference being largest for S, Zn, As, Br and Sb. Also, sectors 5 and 6 had similar ratios at the two

T. A. PAKKANEN

1402

et al.

Table 5. Average elemental ratios to excess vanadium for fine particles as obtained from the SFU samples (ILVS samples for NH,-N, Mg, MO, Ba and Bi at Nordmoen) Sector (see Fig. 6) Samples

I+8

1+2

3#

5

6

1,2,3

12-16

17, 18#

22, 23

5,6

740 420

440 500

NHa-N

Birk Nord

990.D 340. D

600. D 980

Mg

Birk Nord

(390) 320. D

17. D

S

Birk Nord

3100 3200

K

Birk Nord

(150) 620

Ca

Birk Nord

W)

MnX

Birk Nord

Fe

Birk Nord

Ni

Birk Nord

cu

Birk Nord

Zn

Birk Nord

14. D 85

Birk Nord

(2.6) 2.3

Birk Nord

18 48. D

As

Br

MO

Cd

Birk Nord

1.5 D 1.3

I

Birk Nord

Ba

Birk Nord

Pb

Birk Nord Birk Nord

(55) (130)

47 197. #

21* 17

15 17

(47) (75)

25 50. #

(6.4) (3.0) (55) (69)

20 16

125. D 0.3 1 0.09 D

36 79. #

(7.1) 5.4 D

1.1* (1.2)

0.67 (0.82)

12* 10.5

0.69 1.5#

0.37* 0.43

0.39 (0.36)

10.4 89. D#

7.6* 8.7

(4.9)

(1.1)

(0.56) 1.12#

0.38* 0.27

(11) (9.2)

(3.8) (8.5)#

1.8* 1.9

(1.1)

0.25 (0.27) #

0.1* 0.041

(0.092) (0.037)

0.86#

0.12*

0.05*

0.31* 0.78 #

0.26* 0.24

0.09 D (0.18)

1.1* 0.48

0.75 (0.65)

(12) (24) (0.75)

0.31 D (0.79)

1.1 D

(10) 16. D

(2.4) 4.3 # 0.38 0.96 # 6.2 33. # (0.040) 0.32 #

5.1

0.09 D 0.17 0.73

0.13* 0.36 D

0.16 0.03 * 4.2 (5.5)

6.2* (9.8) 0.022*

Birk: Birkenes; Nord: Nordmoen. -: value below detection limit. *: value based on one measurement only. no parentheses or code: lowest value larger than 75% of the highest. ( ): lowest value 50-75% of the highest. D: lowest value less than 50% of the highest. #: trajectories for sector 3 at Nordmoen were slighly spread to sectors

sites due to the high episodic concentrations of these elements in samples 5,6,22 and 23 which masked the local differences. Combined sectors 1 and 8 had much higher ratios of K, Zn (Nordmoen), As, Br, I, and non-crustal

(12) (11) 0.38 0.34

(8.1) (12) 0.79 2.3 D

(2.9) 2.5 #

4.3* 4.6

0.28* 0.34

0.66

Birk Nord

(11) 4.6*

2.4

160 250

-

Sb

740* 495

49 360

2.4 D

(14) (6.7) # 760 1740. #

32. D (8.0)

Birk Nord

Bi

1400. D (2800)

610 1170. #

0.15 0.004*

2 and 4.

(excess) Mn (MnX) and Pb (Nordmoen) when compared to combined sectors 1 and 2. Especially for Nordmoen there was a strong local (or regional) contribution for several elements when the combined sector 1 + 8 samples were collected. In Birkenes, the

The atmospheric aerosol in southern Norway sector 3 ratios for most of the elements fall between the values found in northerly and southerly air masses, which is reasonable considering the location of emission source regions. For Nordmoen, the trajectories of sector 3 samples were spread to sectors 2 and 4 and passed close to Oslo. Nevertheless, the Nordmoen “sector 3” data are included in Table 5 for comparison. The Nordmoen-Birkenes difference for sector 3 data is especially large for K, Zn, Pb and Bi. Since K and Zn are known to be emitted from refuse incinerators it may be possible that also Bi originated from this source.

3.6.2. Comparison of interelemental ratios in air masses coming from U.K. to southern Norway (this work) and to southern Sweden (Swietlicki et al., 1989). The preliminary interelemental ratios measured in this work for the United Kingdom (Table 5, sector 6) and the Great Britain signature of Swietlicki et al. (1989) are compared in Table 6. The original elemental ratios to nickel of Swietlicki et al. were recalculated as elemental ratios to vanadium. In this work, VX and MnX were used, but this had very little impact since the crustal rock contribution to fine particle mode was small for the measured sector 6 values. Sector 6 ratios were similar in Birkenes and Nordmoen and these values were combined to obtain the arithmetic average of four samples. Swietlicki et al. (1989) presented their signatures as a geometric mean of single ratios, but this causes only a small difference. Table 6. Comparison of elemental ratios to vanadium or excess vanadium (VX) in air masses coming from the British Isles for this work as measured for the SFU samples (number of samples in brackets) and for the Great Britain signature of Swietlicki et al. (1989); ratios of Mg, MO, Ba and Bi are from ILVS samples for Nordmoen This work Sector 6 ratios to VX

Swietlicki et al. (1989) Sector G ratios to V

(34) c41 208 [4] 16 [41 6.3 [4] 0.56 [4]

145 431 24.9 12.0 1.09

Mn Fe

0.75 [4] 12 [4]

0.62 9.4

Ni CU Zn Br Pb

0.36 [4] 0.38 [4] 5.0 [4] 0.91 [4] 4.8 [4] 8.6 [3] (0.65) M 0.15 [3] 0.18 [3] 0.07 [4] (0.10) c21 0.17 [S] 0.70 [4] 0.12 [3] 0.10 [3] 470 [4]

0.41 0.36 4.9 1.07 4.9

Element Na S K Ca Ti

Mg Cr As Se MO Cd Sb I Ba Bi NH,-N

1403

Table 7. Comparison of interelement ratios, as measured in air masses coming from the U.K. to Norway, with estimated interelement emission ratios in the U.K.

As/V Cu/v Mn/V Pb/V SbjV Zn/V

Measured in this work in Norway, in 1988

Estimated emission ratios in U.K. in 1979 (Pacyna, 1983)

0.15 0.38 0.75 4.8 0.17 5.0

0.078 0.28 0.49 4.8 0.019 1.7

In this work, the elemental ratios to VX were generally consistent for all four samples, but one outlier had to be excluded from the As/VX and Sb/VX ratios. The Na/VX ratios showed a large variability and therefore this ratio is presented in brackets in Table 6. Ratios for Cd and Cr are based on only two samples and are purely indicative. For the important tracer elements Mn, Cu, Ni, Zn, Br and Pb, the ratios measured in this work are strikingly similar to those of Swietlicki et al. (1989). 3.6.3. Comparison of interelemental ratios in emissions in U.K. and in air masses coming from U.K. to Norway. In Table 7, interelemental ratios measured in this work in Norway for air masses originating from U.K. (sampling in 1988) are compared to element emission ratios in U.K. in 1979 (Pacyna, 1983). There is a difference of 9 yr for this comparison but, with the exception of lead, the emissions are believed to have changed little within this 9 yr period. The agreement is within a factor of 2 for As, Cu, Mn and Pb, but Sb and Zn agree poorly. Concerning Zn, the local emissions near Nordmoen, discussed earlier in this paper, may be one important reason for the disagreement.

4. CONCLUSIONS

During the eighties, the concentration levels of several pollutant elements have been rather stable in southern Scandinavia. In this work, the long-range transport episodes from U.K. and from central and eastern Europe were found to raise the concentrations of pollutant elements to levels that are 20-50 times higher than the background concentrations. The size distributions of the investigated elements, measured using Berner low-pressure impactors, usually showed one or two modes in the fine particle range and one or two modes in the coarse particle range. Relative humidity values higher than about 80% resulted in a significant increase of the MMADs for the largest fine particle mode. The SFU samplers used at the two sampling sites and the LPI sampler used at the Birkenes site showed similar average values for elemental fine particle to total aerosol ratios.

T. A. PAKKANEN

1404

The use of conventional methods showed that important local and/or regional sources of Si, K, Mn, Zn, Br, I, Pb and Bi existed in southern Norway. The existence of most of these sources could be verified by use of the relative size distributions method (RSD method). Interelemental ratios in air masses of different geographical origin were calculated for the two sampling

sites. The elemental ratios in air masses coming from U.K. to southern Norway (this work) and to southern Sweden (Swietlicki et al., 1989) were strikingly similar for several pollutant elements. Also, for some elements the emission ratios in U.K. were similar to the interelemental ratios measured in this work for air masses coming from U.K.

et al

Harrison R. M. and Sturges W. T. (1983) The measurement and interpretation of Br/Pb ratios in airborne particles. Atmospheric Environment 17, 3 1l-328. Heidam N. Z. (1981) Review: aerosol fractionation by sequential filtration with Nuclepore filters. Atmospheric Environment 15,891-904. Hillamo R. E. and Kauppinen E. I. (1991) On the performance of the Berner low pressure impactor. i2erosol Sci. Tech&.

14, 33.-47.

Hillamo R. E., Pacyna J. M., Semb A. and Hanssen J. E. (1992) Size distributions of inorganic ions in atmospheric aerosol in Norway. In Development of Analyticul Techniques for Atmospheric Pollutants (edited by Allegrini I.), Air Pollution Research Report 41, pp. 51-65. Commission of European Communities, Brussels. John W., Hering S., Reischl G. and Sasaki G. (1983) Characteristics of Nuclepore filters with large pore sizes .-- II. Filtration properties. Atmospheric Environment 17, 373-382.

Acknowledgements-The measurements presented in this paper were financially supported by a grant from Norges allmennvitenskapelige forskningsrld (NAVF) and by the Maj and Tor Nesslings foundation. W. M. and G. D. acknowledge support from the Belgian “Nationaal Fonds voor Wetenschappelijk Onderzoek”, the “Interuniversitair Instituut voor Kernwetenschappen”, the “Instituut tot Aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw”, and the Impulse Programme “Global Change” supported by the Belgian State, Prime Minister’s Service, Federal Office for Scientific, Technical and Cultural Affairs. Thanks are also due to Dr Sylvain M. Joffre for his constructive comments and to Mr Jan Cafmeyer for technical assistance.

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