2010 SEM-EDX Identification of FP

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Air Pollution and Climate Change

269

SEM-EDX IDENTIFICATION OF PARTICLES FROM FOG IN AN

INDUSTRIALLY POLLUTED REGION OF CZECH REPUBLIC

Assoc. Prof. Dr. Valeria Stoyanova1

, Dr. Annie Shoumkova1

,Eng. Dr. Jaroslav Fisak

2, Tsenka Tsacheva

1

1Institute of Physical Chemistry “Rostislaw Kaischew”, BAS, Bulgaria2 Institute of Atmospheric Physics, AS CR, Czech Republic

ABSTRACT

The properties of individual particles, rather than bulk aerosol characteristics, determine

the environmental and health impact of the atmospheric pollutants. Single particles have

been sampled during 30 fog episodes at the mount Milesovka (837 m a.s.l.) located in

the industrially polluted area of north Bohemian brown coalfield. More than 2000 ofthese solid, water insoluble particles, collected from May 2006 till July 2007, have been

analyzed by SEM-EDX and classified according to their shape, size and elemental

composition. Here we summarize results related to the presence of some heavy metals

and other trace elements and their correlation to wind speed and direction, t given

meteorological conditions. Particles, rich of Cu, Zn, Ba, Pb, Co, Ni, Fe, Ag, Au, Ce, Gd,

etc., have been detected. Most of the identified heavy metals present in particles smallerthan 5 μm. It has been established that some elements exist separately or in specific

combinations that, along with the information for particle’s backward trajectory, could

be used for recognition of the atmospheric pollution sources.

Keywords: SEM-EDX, solid atmospheric pollutants, trace elements, heavy metals,Czech Republic.

INTRODUCTION

The changes in chemical composition of the atmosphere have important contribution to

air quality and climate changes [1,2]. Solid aerosols play a central role in adverse health

and visibility. They are associated with a variety of anthropogenic activities (traffic,

industry, power plants, mining, combustion, etc.) and/or natural processes (volcanoes,

forest fires, sea spray, etc.) [3]. Ejection of giant amounts of anthropogenic heavymetals in atmosphere is still an unsolved problem bothering the European community.

Knowledge about the nature of such pollutants is essential not only for their monitoring but also for the modeling of atmospheric processes.

It is well known that the properties of the individual particles, rather than the bulk

aerosol characteristics, determine the optical, environmental and health effects of one

aerosol. Scanning electron microscopy (SEM), coupled with Enegry Dispesive X-ray

Spectrometer (EDX), has proven to be an ideal tool for characterization of individual

particles [4-7], providing simultaneously precious information for their composition,

shape, structure and size that cannot be obtained by any bulk analytical approach.

In this paper we pay attention to the usage of the solid atmospheric pollutants as tracers

for specific emission sources, especially when they are of inhalatory size and have

specific morphology and composition.



International Multidisciplinary Scientific Geo-Conference SGEM 2010

270

SAMPLING AND ANALYSIS

Solid particles, known as PM10 or PM2.5 (particulate matter, smaller than 10 or 2.5

μm), transported by fog water droplets have been studied. They have been collected at

Milesovka observatory, located in North Bohemian brown coalfield – one of the most

polluted areas of the Czech Republic till the nineties. Several large conurbations (Most,

Usti nad Labem, Litvinov, Teplice, etc.), power plants and intensive chemical industry

are concentrated there and additionally a high traffic road for trucks passs along.

In total 30 fog samples were gathered during fog episodes from May 2006 till July 2007 by using of special active and passive devices. The insoluble particles have been caught

by filtering of fog water through nitrocellulose filters (pore sizes 0.45 m), dried,

covered with carbon coating (onto the filter) and studied. The soluble constituent of

some of these fog water samples has been previously analyzed [8]. The comparison of

water-soluble and insoluble contents in fog samples is an authors’ aim in progress [9-

10]. The aim of the current investigation is to provide information about composition

and properties of atmosphere solids that, along to the data for the meteorologicalconditions, will contribute for the identification of the air pollution sources, which is our

final goal.

All analysis of fog particles (FP) has been carried by mean of JEOL JSM 6390. The

elemental spectrum of each particle was collected for 30 s at 20 KeV. The size andshape of each particle were determined manually during its observation by SEM (using

SEI- and BEI- mode) and from the microphotographs. Most of the morphologicalcharacteristics (shape, size, surface, axis relation, etc.) are better visible in SEI- mode,

formed by secondary electrons. At appropriate conditions, the FP rich of iron and/orother heavy metals could be easily detected in backscattering mode (BEI), formed by

back-scattered electrons. In this mode, particles (or pieces of them), enriched inelement/s, having atomic number bigger than that of the iron, are represented as bright

spots on dark background. All non-ferrous heavy metal FP have been identified in BEI-

mode, because of their low frequency and small sizes. More details for the used

apparatus and methods of analysis of micro- and nano-size FP are given in our previous

publications [6,7].

EXPERIMENTAL RESULTS

Between 50 and 150 particles have been analyzed in each of the 30 fog samples, and

totally more than 2200 FP have been studied. FP collected from one single wind

direction have been classified into groups: East (97), South (188), West (1192) and

North (289) (see Table 1, Fig. 1). FP collected from more than one wind sector areincluded in the data, presented in Fig. 2. All carbon-rich particles (organics, soot, etc.)

are excluded from data reprocessing in this presentation. In Table 1 somemeteorological conditions measured during fog samples collection are given together

with the electron-microscope data for the studied FP from each sample and theirdistribution in the four main groups. Each wind direction main group is divided into

three principal (vertical) groups: particles enriched in Fe (Fe > 50 wt.%), particles of

non-ferrous transition and heavy metals, and particles enriched in Al+Si > 50wt% (the

rest of particles, not fulfilling these criteria, are excluded from this table). The percent

of spherical particles (indicative for high-temperature processes) is shown in breaks

after the number of analyzed FP for every sample and group of particles. An averaged

value of the mean particle size is added in the last column of Table 1.




271

Table 1. Meteorological conditions and electron-microscope data for the studied FP,their distribution in the four main wind sectors and in three principal groups – FP

enriched by Fe, by Al+Si and by heavy metals, together with the mean particle size.

Sample

Fog

sampling

date

Wind

speed,

m/s

Wind

direction,

degrees

Sampling

time,

hours

StudiedFP/spheres

Fe-richFP

Other

heavymetal

FP

Alumo-

silicate

FP

Mean

size,

m

East 97 (17%) 15%(40%) 3%(30%) 66%(14%)

1 28/05/07 10.5 95±77 7.25 97 (17%) 15 (40%) 3(30%) 64(14%)

1.6

South 188 (30%) 24%(41%) 16%(47%) 58%(28%)

2 23/10/06 10 192±37 3 92(39%) 22(45%) 15(47%) 59(41%)

3 28/11/06 6 183.5±32.5 12 96(21%) 24(42%) 15(47%) 50(12%)

2.2

West 1192 (22%) 18%(31%) 9%(24%) 54%(25%)

4 30/08/06 12 296±6 4.75 79(43%) 11(54%) 6(0%) 76(37%)

5 06/09/06 9 304.5±12.5 5 77(29%) 18(28%) 5(0%) 57(28%)

6 21/10/06 11 238+12 5.5 79(39%) 34(38%) 17(71%) 49(29%)

7 24/10/06 13 236±17 1.5 89(43%) 23(35%) 9(55%) 85(32%)

8 12/12/06 11 271±

25 16 99(14%) 9(44%) 10(20%) 53(11%)9 09/01/07 14.5 252±4 8.5 97(5%) 10(10%) 20(0%) 38(0%)

10 17/01/07 19 250±6 25 107(14%) 20(25%) 7(14%) 72(12%)

11 15/05/07a.m. 9 292.5±4.5 4.5 91(12%) 9(33%) 7(0%) 36(14%)

12 16/05/07 10 294±3 7 102(15%) 11(36%) 9(22%) 83(11%)

13 25/06/07 5 244.5±9.5 8.5 84(20%) 9(11%) 3(33%) 68(21%)

14 02/07/07 7.5 245.5±11.5 29.25 75(7%) 11(9%) 5(20%) 36(8%)

15 05/07/07 8.5 287±8 4 96(11%) 16(12%) 6(50%) 46(9%)

16 29/07/07 8 273.5±42.5 7.25 117(37%) 35(43%) 2(100%) 94(27%)

3.8

North 289 (13%) 9%(19%) 9%(12%) 53%(14%)

17 04/04/07 6.5 354.5±16.5 3.5 53(26%) 13(38%) 7(0%) 26(31%)

18 29/04/07 8 349.5±7.5 3 73(5%) 9(0%) 9(11%) 29(10%)

19 15/05/07p.m. 12.5 330.5±19.5 6.25 83(16%) 8(12%) 6(33%) 42(17%)

20 03/06/07 9.5 358±

34 7.25 80(7%) 6(17%) 3(0%) 57(7%)

4.2

Figure 1. Normalized data for heavy metal FP according to the main wind sectors.

Cr Mn Ni

Cu Zn Ag

I Ba Pt

Au Pb Fe

Cr Mn

Ni Fe

Cr Mn Co

Ni Cu Zn

Zr Ag Sn

Sb I Ba

W Ce Au

Pb Fe

Cr Mn Co

Ni Zn Y

Zr Fe

N

W

E

S




272

Figure 2. Elemental composition of all (2206) particles studied microscopically.




273

Fig. 1 presents in broad outline the distribution of the studied FP enriched of iron andnon-iron heavy metals according to the main four wind sectors. The elemental spectra

obtained from more than 2200 FP, including samples covering more than one wind

sector (that are not presented in Table 1 and Figure 1), are illustrated in Fig.2. The

legends in the Fig. 1 and Fig. 2 mark the elements by different colors or patterns.

Typical FP shapes (faceted, rounded, dendritic) and surfaces (smooth or rough) are

presented in Fig. 3. Their macro composition is given in weight percents up-left on each photo, while up-right is indicated the first letter of the corresponding wind sector. The

FP size is in the micrometer scale and indicated by marker line below each photograph.

Figure 3. Heavy metal FP (looking as white spots in BEI–mode) with differentcomposition, given in weight percent up-left on each photo. The FP size is indicated by

the corresponding marker line below each photograph.




274

DISCUSSION AND CONCLUSIONS

Every atmospheric particle brings its own valuable information that, after statistical

accumulation of data, contributes the clarifying of pollution status. For example, NaCl

particles (10 found in this study) can direct our attention to the salting of the roads

during winter period. Other typical markers appear to be carbon-rich particles that are

born due to the intensive anthropogenic activity (coal and other fuels burning) in

heating periods from autumn to spring. (The analyses of carbon-rich FP are not includedhere, although they represent a significant part of the investigated fog particles.)

Similar is the role of particles enriched in specific combinations of heavy metals is

indicative for the source of pollution, especially if the transport history of FP can be

evaluated. The information for the shape, size and surface peculiarities of the studied FP

is also important for their identification. For example, the spherical shape of micro- and

nano- particles usually results from high-temperature processes, and therefore could be

almost directly correlated to an anthropogenic origin. Nevertheles, an explicit

conclusion, must be supported by data for the chemical composition of the particle.

Almost all FP studied represent PM10, more than 60% of them are even PM2.5 (mean

particle size 3.6 μm). As such fine particles have been in contact with acidic water (pH

~ 4) for a long time (from hours to days) [8], they probably have passed through various

physicochemical transformations (dissolution, pre-crystallization, etc.), and actuallyrepresent not primary (as emitted) but secondary particles. This note should be taken

into account when a FP and PM from industrial sources are compared.

The small number of FP collected in some sectors additionally hampers the statistical

processing of data for evaluation of the mean FP size. Nevertheless, a tendency has been

established (Table 1, last column), showing that in general the smaller particles belong

to the South-East and the bigger - to the North-West group. Most probably this result isrelated to the more intensive wind flows from West, lifting bigger particles from the

crust and soils in atmosphere. The relation size-pollution source is less probable.

Some of the detected elements (Fe, Cr, Mn, Ni) present in all studied samples,

independently on the wind direction during the respective fog episode. Others FP are

common for two wind sectors, e.g. Cu, Ag, Ba, Au and Pb (North-West) and Co and Zr

(South-West). Third elements have been encountered in a single sector only, e.g. Sn, W,

Ce (West), Pt (North), Y (South). One quarter of all non-ferrous heavy metal FP are rich

of Zn, a fact corresponding to the recently published reports for the absence of clear

tendency for Zn-pollution decreasing in European Union since the beginning of the

nineties [11,12]. Analyzing rain waters, one of these authors [12] has confirmed thedecrease in Cu, Pb and Cd pollution that use to be a serious environmental problem in

Czech Republic [13,14].

The West sector is the most abundant in heavy metals (without Fe) as number of

elements (16), distributed in 9% of all studied 1192 FP. This result is expected, having

in mind the prevailing west winds, located in this direction intensive industry, including

several power plants, and heavy traffic. According to [15,16], traffic appears to be

responsible for particles enriched in Ba, Cu, Cr, Pb, Sb and Zn, while Ni and Sn are

being emitted most probably by the industry. This result is supported by the typical

microstructure (rounded shape and small sizes) of some FP from West direction (see

Figure 3).




275

The number of Fe-rich FP in North sector is relatively low and equal to that of heavy-

metals-rich FP. The percent of spherical particles in all types of FP is the lowest (12-

19%), indicating smaller contribution of industrial high-temperature burning processes

to the atmosphere pollution. Eleven different heavy metals (except Fe) have been

detected in four samples analyzed.

The East sector is characterized by the lowest amount and variety of heavy metal FP (3,

excluding Fe-rich ones, 3% of 97 studied FP). This concentration is up to 3-5 times

lower than in the other sectors. Only 3 particles (enriched in Cr, Mn and Ni) have been

found there. Although on the base of one analyzed sample only it is difficult to conclude

that pollution episodes from East are rare, it seems so.

The most interesting results have been obtained from the analysis of FP from the South

sector, where heavy metal FP (excluding Fe-rich ones) cover 16% of all studied FP

(188) (see Table 1), and seven different heavy metals have been detected (see Fig. 1) in

only two samples. This fact is supported by the greatest concentration of spheres (30%)found in all types of FP in the South samples (see Table 1). The spherical particles in

Fe-rich FP reach 41%, and 47% in heavy - metals bearing particles. These

microspheres, resulting usually from high-temperature combustion processes, oftencontain toxic elements, condensed on their surfaces [17,18] that could be readily

extracted in acidic soil solutions or in the lung.

In conclusion, solid particles, caught by fog, could be used successfully in air pollution

monitoring – especially those, enriched in heavy metals that can act as valuable markersfor industrial contamination of the atmosphere.

ACKNOWLEDGEMENTS

The participation in SGEM-2010 has been realized with the financial support of ProjectTK-X-1713 funded by Bulgarian Ministry of Education and Science.

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2010 SEM-EDX Identification of FP