Cascade impactor measurements of the size distribution of the major classes of organic pollutants in atmospheric particulate matter

Atmospheric Environment Vol. 12.pp 2229-2139 Q Pergamon Press Ltd 1978. Pnotcd I” Great Bntam

CASCADE IMPACTOR MEASUREMENTS OF THE SIZE DISTRIBUTION OF THE MAJOR CLASSES OF ORGANIC POLLUTANTS IN ATMOSPHERIC PARTICULATE MATTER L. VAN VAECK and K.

VAN

CAUWENBERGHE

Department of Chemistry, University of Antwerp (U.I.A.), B-2610 Wilrijk, Belgium (First received 4 January 1978 and in firm1form 9 May 1978)

Abstract - Airborne particulate matter from a suburban area was fractionated in a 6-stage high volume cascade impactor and analysed for about 60 organic pollutants by programmed m~tip~e ion detection gas chromatography-mass spectrometry. The distribution. as a function of particle size, has been measured for the aliphatic hydrocarbons, carboxylic acids, polynuclear aromatic hydrocarbons (PAH) as well as some aza-heterocyclic polyaromatics. The observed distribution patterns are very similar. Most aliphatic hydrocarbons (85~90%) arefound on particles below 3gm. The carboxylic acids are found for 90-95x below 3~. The PAH dist~bution is strongiy subjected to seasonaf variations: 95-98x below 3pm and 70-80x below 1 m in winter. For the PAH eight different,but closely related types of distributions were measured. In winter, the distributions shift toward the smaller particles. Indications for artclaets produced by volatilisation are advanced : the lower PAH show a flatter distribution in the smaller size range. Also, the alternating concentration levels of even and uneven n-aikencs co& be due to seIective losses for the even alkenes, sina there is a correlation with the molar heat of vaporisation of the homoiog series.

Health effects related to the inhalation of ambient aerosols are largely dependent on the size of the particles on which the compounds are found. For many of the inorgan~cconstituents ofambient aerosols the study of the distribution pattern can be useful both with respect to the toxicology of aerosols as well as to their origin and history (Dams, 1974). The information available in the open literature on the distribution of organic pollutants over different particle sizes in ambient aerosols is rather scarce. Major reasons for this are the complexity of the organic fraction of aerosols and the lack of simple analytical procedures for the quantitative determination of these compounds. In the last years, a major goal of our research efforts was to establish a reliable and sensitive q~ntitation method for the organic fraction of ambient aerosols based on gas chromatography-mass spe-ctrometry. We have now applied this method in an advanced form (preprogrammed multiple ion detection) to the measurement of individual organic pollutant concentrations of the different stages of size fractionated ambient aerosol samples. The purpose of this study is to present a detailed report on the distribution of the major organic compounds in ambient particulates. However, from our measurements it follows that many of the observed distribution patterns show variations that can be expiained by gas phase contributions of the com-

pounds. This means that there may exist a quantitation artefact (biow-oSS) on a high volume cascade impactor that affects the observed distribution shapes. This effect has been recognised by Cautreels and Van Cauwenberghe (1978) for hi-vol filtration sampling and its contributions to quantitative data shown to be non negligible. Finally, one should remember that only compounds with sticient volatility are measured by the GC-MS technique. This fraction however does not account for half the weight of the extractables in organic solvents. Thus, analysis of all the organic compounds is still far away and further development of the CC-MS technique will be needed to give more information about these non volatiles in the future.

EXPERIMENTAL Sampling Airborne particulate matter was sampled with a high volume cascade impactor series 230 of Sierra instruments

Inc.,consisting of 5 stages with rectanguiar jets and a back-up filter. The equivalent aerodynamic cut-off diameters at 50% collection efficiency for a flow rate of about 40 SCFM are given in Table 1 (the specific gravity of the particles is assumed to be I gem - 3). As the collection media, Whatman glass fiber titters (type GF/A), pre-extracted with methanol, are used. The total volume of sampled air passed through a rotameter (Rota, type RHN G4 10,000,Germany) equipped with a photorelay. Sampling is interrupted when the Bow rate decreases more than 5%for at least 4min as would occur in the case of reduced pumping speed due to back-up filter

2229

L. VAN VAECKand K

2230

1.

Table 1.

Sierra

Hi-V01 cascade characteristics

impactor

Stage number

Equivalent aerodynamic cut-off diameters at 50% efficiency Olm)

1 2 3 4 5 6

> 7.2 7.2 -3.0 3.0 -1.5 1.5 -0.95 0.95-0.49 < 0.49

clogging or reduced motor efficiency. The sampled air was led away from the sampI@ unit by a pipe about 2m long. Typical sampling times arc &days, corresponding to a volume of about 10,OOOm”.This results in loadings of about 100 mg on each stage. The back-up filters arc changed every 3 days. Filters arc wcighcd to 0.1 mg after equilibration. Sampling was performed on the university campus located in a suburban residential area. Emission sources in the vicinity include a+micipal incinerator plant half a mile away and several industrial plants in the port region of Antwerp at about 15 miles. In Table 2 sampling periods as well as concentrations of total suspended matter (TSP) arc given. Chcinicai amafysis The filters arc extracted in a Soxhlct apparatus during eight hours with benzene (“Zur Riickstandsanalysc”, Merck) and with methanol (p.a. Merck) consecutively and the extracts combined. The extract is concentrated by evaporation under reduced pressure to dryness and redissolved in redistilled dicthylether @.a. Merck). Most inorganic compounds arc removed by washing the extract with water. The water layer is discarded. The acids arc methylatcd by addition of an excess of diazomcthanc in ether. As intcmaf standards a solution of d&crated mcthyloctadccanoate-d, (isotopic purity 98.9%) and dcutcratcd pyrcnc-d, (isotopic purity 99%) is added. The volume is finally reduced to about 1 ml. From this, 1-3 ~1 is used for analysis. The GC-MS instrument is a Fmnigan 3100 quadrupole type mass spectrometer coupled on line with a Finn&an 6OW Ddatasystcm. TheGCiscquippcd witha 3 m packed column filled with 2.5% Dcxsil 300 GC on Gas chrom.Q (100-120 mesh). The temperature is programmed from 120 to 280°C at 4”Cmin-‘. The helium flow rate is 25mlmin-‘. The GC conditionsarcchoscn tooptimixcscparation efficiency within a maximum analysis time of 45 min. The mass spectrometer is used in a software controlled multiple ion detection mode (MID). The possibilities of the MID program offered in the Finnigan software were further developed to obtain a highly flexible MID version permitting

VAN

CAUWENBERG~

time measurement of a large number of compounds (up to 60) simutt~~~~y within the provided analysis time. For quantitative calibration, curves passing the origin arc constructed daily by injection of 3 standard solutions. The accuracy of the W-MS analysis is evaluated to be within lo”/, as described earlier bv Van Vaeck er ol. 11977). All the rc$rtcd results are corrcckd for blank contri‘butio& of the aliphatic hydrocarbons and carboxylic acids. RESULTS AND DISCUSSION

The collection efficiency of the cascade impactor was compared (Van Vaeck et al., 1978) with a “high-volume” sampler for filtration on glass fiber filter of the type described by Dams et al. (1973) using circular filters of 1I cm dia. As shown in the last two columns of Table 2 the total amounts of particulate matter collected by the two devices during the same periods agreed within 10% in spite of the differences of flow rates and shelter geometry. The equivalent aerodynamic cut-off diameters at 50% collection efficiency of the different impactor stages are based on the manufacturer’s data. These agree with the calibration carried out by Willeke (1975). Concentrations of the individual pollutants can be expressed in ngme3 of air or in pgg- l particulate matter on each stage. Our experience is that the first method (ngme3) is more reliable because the occasional adhesion of glass fiber filters to the impactor plates will cause losses of the co&&on substrates and reduce the accuracy of weighing the collected particulate matter. With the Hi-V01 cascade impactor only 6 fractions are obtained. The distribution pattern based on these data, will be somewhat less well defined than in the case of a low volume 8 stage impactor, but the flow rate of the latter (1 CFM vs 40 CFM for the Hi-Vol) lengthens the sampling time too much. Furthermore, the upper-cut-off size for stage 1 (> 7.2pm) and the lower cut-off size for stage 6 (c0.49pm) of the Sierra impactor have not been determined experimentally. For these, the fair assump tions of 50-IOOpm and about 0.01 ,um respectively will be made in agreement with Lundgren et al. (1975). Practically, the most useful information is obtained for the well determined fractions in the size range below 7pm, containing the particles penetrating the non ciliated pulmonary region (AEC standard, Lippmann, 1970).

Table 2. Volumetric and gravimetric data of the samples Sample code

S, s2

s3 S,

P&Xi

October 14-25, 1976 December 22-30, 1976 March B-15, 1977 March 15-22, 1977

Total volume (m’) 9888 I 1,242 11,362 %77

TSP Ocgm-“) fmpactor Filtration

62.4 104.1 72.1 51.2

59.6 116.8 64.3 53.3

2231

Size distribution of organic pollutants According to Whitby et al. (1974) distribution patterns have to be described in different manners to allow a valid interpretation. In this paper, primarily the concentration vs particle size and cumulative mass distribution representations will be used. The derivative curve of the latter, namely dM/dlogD+, vs 1%D&lP, = particle diameter) suffers from the relatively low number of data points and will not be discussed for individual compounds. Other measurementssuch ~countingof~rticl~ofa~vens~ecould not be carried out. At present, we only studied the compounds found in the particulate phase. No effort was undertaken to evaiuate concentrations levels of these compounds in the gas phase. The experiments described by Cautreels and Van Cauwenberghe (1978) using a Tenax adsorp tion column mounted after a filtration Hi-V01 sampler allowed the evaluation of pollutants present either as gases or resulting from evaporation of the collected sample. Primarily, the lower ahphatic hydrocarbons (up to 50% for docosane and lower homologs), the lower carboxylic acids (up to pentadecanoic acid) and some polynuclear aromatic hydrocarbons (PAH) such as phenanthrene, anthracene, fluoranthene, pyrene and methylated derivates of these are found in significant amounts on the adsorption column and thus are present in the gas phase. In the following paragraphs we will discuss consecutively : 1. The distribution of the weight of total suspended particulate matter as function of particle size; 2. The total concentrations of individual ~liutants obtained by summing up all stages and normalising for the volume of air; 3. The distribution patterns for individual pollutants are given as: (a) concentration vs particle size or stage number: here the data are represented in their most straightforward form ; (b) cumulative mass distribution : here percentages of a compound on particles smaller than a given diameter are listed. 1. The distribution

Fig. la. Especially in the winter sample Ss, the TSP is high for stages 4,s and 6 ( < 1.5pm). In all samples, the TSP increases with decreasing particle size, with a m~imum in the submi~ron range. However, this figure is somewhat misleading because the size range of the particles on each stage is not taken into account. Therefore, data are also represented in a “Lundgrcntype” mass plot (Lundgren et al., 1975), namely

-J GL-5L--4L--3L-2Lnumber

Sage

i

_

I

I

i

---1 I----,

I

I

of total suspended particulate

matier

Total suspended particulate matter values, collected on each stage are mentioned in Table 3 and plotted in

Fig. l(a) Size distribution of the total suspended particulate matter. (b) Lundgren plot of the total suspended particulate matter.

Table 3. Distribution of total suspended particulate matter over the impactor stages (TSP, pgrne3) Sample code

6

S*

17.00

ii.33

t0.i 1

; %

32.29 16.31 16.42

18.88 10.01 I.693

18.88 9.68 8.27

5

Stage number 4 3

2

1

6.73

9.86

7.41

1.15

3.3

11.21 6.81 4.92

12.28 12.67 8.63

10.59 10.53 6.94

1.02 1.35 1.07

4.4 7.3 6.9

MMED’

cret

* Mean mass effective diameter. t Geometric standard deviation (ratio of particle diameter at 84% to particle diameter at 50%). $ Incorrect value caused by filter losses.

2232

L. VAN VAECK; and K. VANCAUWENBERGHE

aromatics

l Sum of all stages. t Fraction below given particle

+acridine

containing

benzoquinoline phenantridine benzacridine dibenzacridine

Nitrogen

fluoranthene pycene benzo(a)fluorene benzo(c)fluorene methylpyrene chrysene + benzo(a)anthracene benzo(b + k)fluoranthenes benzo(a +e)pyrenes perylene o-phenylenepyrene benzo(ghi)perylene dibenzanthracene picene

_^ __

size.

1.77 0.16 0.84 0.42

--

1.79 1.32 0.8 1 0.80 0.35 10.04 17.52 12.63 0.36 1.40 5.58 1.90 1.39 86 90 93 95 ~-

90 92 91 90 91 94 95 95 93 94 96 95 95

_.

72 62 64 71 --

58 59 54 55 58 66 70 66 66 60 72 71 62

-_ --

4.41 0.80 3.92 2.10

12.69 10.84 5.17 5.10 2.66 48.27 65.80 43.84 2.98 11.93 23.22 7.36 7.57

_-

97 97 96 98

95 96 96 96 96 96 97 97 94 97 96 98 98

__

72 74 70 70

72 72 69 68 71 72 73 72 51 65 72 74 74 1.56 0.11 0.99 0.60 ~__

2.23 1.75 1.09 0.79 0.47 9.19 12.38 IO.99 0.81 I.81 4.95 I .42 I.14

__

62 62 71 62

70 60 66

94 88 93 91 92 95 88

60 62 58 58 58 68 70 68 64

90 91 92 92 90 95 96 95 94

.- ._

95 95

5.34 2.33 2.10

^_

96

14.13

0.53 0.30

93 _ 93 81

90 91 92 92 94 92

1.91

90

I ;58 1.27 0186 0.68 0.28 8.11 12.34

_-

62 -. 68 56

74 76

72

60 61 57 60 61 68 70

w k’ 0 P Z 5 5. ?I P

L. VAN VAECKand K. VAN CAIJWENBFARGKE

2234

dM/d log D, vs log D,, in Fig. 1b. The upper and lower cut-off diameters for the sampler are assumed to be 100 and 0.01 pm respectively. The winter sample S2 shows a nearly normal distribution with a maximum between 1 and 1.5 pm. For the samples S 1, S, and S1 a bimodai dist~bution is found with a second maximum between 3 and 7.2 pm. However, because of the low number of fractions obtained from the Hi-V01 cascade impactor, this bimodaiity may not be overemphasized. When the cumulative mass distribution is plotted on log-probability paper, the data allow a straight line approach, giving an indication of log-no~aiity. The mean mass effective diameter (MMED) and geometric standard deviation (a,), determined graphically, are also listed in Table 3. Again, the number of fractions is insufficient to make general conclusions. 2. The total concentrarionsof individualpollutants In Table 4 the first column for each sample lists total concentrations for individual pollutants. These were obtained by summing all stages and normaiising for the volume of air (ng mq3).

In the class of aiiphatic hydrocarbons, concentrations increase with chain length to a maximum at C 29. The uneven homoiogs are found in greater amounts than theeven. A tentative explanation for this could be the selective evaporation of the latter compounds already collected on the filter, since there is no evidence for such alternations in the concentration levels at the emission sources. Furthermore, if the amounts present in the gas phase and these in the particulate matter as given by Cautreeis and Van Cauwenberghe (1978) are summed, a continuous pattern 1sfound from C,, to C2s. Since the increment per carbon atom of the molar heat of vaporisation is always higher, when going from an even homoiog to an uneven than going from an uneven to an even, the hypothesis is put forward that the even aikanes vaporise preferentially with respect to the uneven. Therefore the higher con~ntrations for the uneven aikanes relative to the even could be due to an artifact of the sampling method. For the carboxylic acids, higher amounts of the homoiogs with an even number of carbon atoms are

for individual stages in winter sample S2 (ng m-“)

Table 5. Pollutant concentrations

Stage number 4 3

2

I

0.89 0.81 1.23 0.98 0.85 0.98 0.60 0.72 0.41

0.27 0.6 1 0.56 0.72 0.68 0.59 0.83 0.44 0.65 0.29

0.26 0.52 0.38 0.48 0.50 0.41 0.61 0.29 0.47 0.21

0.39 0.30 4.58 0.38 3.84 0.36 1.06 0.36 2.03 0.82

0.39 0.30 3.29 0.43 2.8 1 0.21 0.51 0.16 0.85 0.34

0.48 0.32 3.27 0.29 3.55 0.16 0.45 0.11 0.60 0.24

0.51 0.32 2.52 0.24 2.36 0.12 0.30 0.06 0.39 0.16

2.96 2.33 1.13 1.13 0.48 9.86 10.55 5.70 0.81 1.96 2.59 1.25 1.07 0.72 0.47

0.69 0.52 0.28 0.27 0.16 2.09 1.59 1.20 0.29 0.44 0.97 0.32 0.26 0.13 0.13

0.37 0.26 0.14 0.13 0.08 1.00 0.89 0.67 0.10 0.23 0.52 0.15 0.16 0.04 0.05

0.25 0.18 0.09 0.09 0.06 0.68 0.66 0.51 0.08 0.18 0.38 0.12 0.12 0.02 0.04

6

5

4.95

7.01 6.52 5.91 4.54 3.71 5.54 2.41 4.41 0.90

1.73 2.64 2.42 2.94 1.85 1.71 2.32 1.18 2.00 0.38

1.15 1.82 1.81 2.26 1.55 1.54 1.80 1.15 1.59 0.35

0.41 0.94 14.76 1.30 11.80 1.27 3.93 1.42 7.43 3.01

0.62 0.41 6.82 0.52 4.87 0.51 1.50 0.57 3.07 1.21

5.51 4.40 1.93 2.05 1.11 23.38 23.11 11.42 0.88 3.09 5.69 2.58 4.16 1.75 0.91

4.53 3.87 1.69 1.71 0.78 15.92 13.71 7.25 0.53 1.38 3.13 1.62 2.35 1.03 0.52

Aliphatic hydrocarbons

tricosane tctracosanc pentacosane hexacosane heptacosane octacosane nonacosane triacontane heneitriacontane dotriacontane

0.56

Carboxylic acids

myristic acid pentadecanoic acid palmitic acid heptadecanoic acid stearic acid nonadecanoic acid eicosanoic acid heneicosanoic acid docosanoic acid tricosanoic acid Poljv3romatics fluoranthene pyrene ~nzo(a)fluorene benzo(c)fluorene methylpyrene chrysene and benzanthracene benzo(b+ k)fluoranthene benzo(0 +e)pyrenes peryltne o-phenylen~yrene benzo(ghi)perylene dibenzoanthracenes picene benzacridine dibenzacridine

(a)

2235

Size distribution of organic pollutants Alwhat%

found compared to the uneven homology. Apart from the excess at C,, and Cts, high amounts are found for C,, and C&. For the polynuclear aromatic hydrocarbons (PAW), the concentration levels for the higher mol. wt compounds are higher than for the lower mol. wt PAH. Losses of the latter by eva~~tion during sampling can be expected. Roughly, the relative amounts are the same in all samples : in each case high amounts of the benzopyrenes (sum of a- and eand benzofluoranthenes isomers), (b+k) benzo(ghi)perylene are detected. The concentration ranges for all compounds agree well in the three samples St, S3 and Sq. However, in a typical winter sample such as SI, concentrations are roughly doubled for the higher aliphatic hydrocarbons (from pentacosane)as well as for the uneven carboxylic acids (from nonadecanoic acid). The most important phenomenon however, is the fivefold increase of the PAH. These results are confirmed by the analysis of independent Hi-V01 filtration samples from the same period. Our results are in contrast with these reported by Pierce et al. (1975): in Toronto the concentration levels for PAH in suburban areas are about 15 times lower and no such large variations between winter and summer samples are found as in Wih-ijk.

hydrocarbons

number sampies,

Staqe

stooe

2

I

3. Distribution patterns Distribution patterns are obtained by plotting measured concentrations vs stagenumber, found in the partide size range below 3 and below 1 ,um. Furthermore, cumulative mass distributions will be discussed. Typical size distribution data for the concentration levels of the major organic compounds are shown in Table 5 for the winter sample Sz. Distribution curves for the other samples are similar and will not be reported here in detail. However, results for all four samples will also be expressed as the percentage of the amount of pollutant. 3.1. Characteristic distribution shapes, Aliphatic byA summary of the data is presented in Fig. 2. For the sample S4 con~trations for the even homologs hexacosane and triacontane, and the uneven homologs tricosane and heptacosane vs stagenumber are shown. The shape of the distribution curve is similar in all samples and seems to be reproducible. Furthermore, three plots are given for the concentrations on stages 6, 4 and 2 vs carbon number in sample S,. The n-paraffins with uneven carbon number are found in greater amounts than the even ones and the pattern is rising with growing chain length. Also the ratio of the concentration levels of alkanes found in the smallest particle size range (stage 6) to this oo the greater particles (stage 1) increases as the chain lengthens. drocarbons.

Carborylic acids. Again the shape of the distribution is similar for different samples but here con-

Number

Fig. 2.

Summary

of corbonr

of size distributions hydrocarbons.

of

aliphatic

centrations are also similar. Typicai distrjbutions are shown in Fig. 3. As for the aliphatic hydrocarbons a plot of the concentrations on stage 5,3 and 1 vs carbon number is represented for sample S,. The scale of the uneven acids (vertical lines) is expanded tenfold with respect to the even acids. For this class a second order maximum for stage 2 (3-7.2 pm) was found. PAH and nitrogen containing aromatics. More variations in distribution patterns are found for the PAH. Each of the observed experimental curves agree in detail with one of the 8 type distributions given in

L. VAN VAECK

2236

and K.

654321 number

Number

Of carbons

Fig. 3. Summary of size distributions of carboxylic acids.

Fig. 4, which can be easily rationahsed as follows. From type I to VI the distribution shifts toward smaller particle sizes. When in type I, the amounts on stages 6 and 5 increase with respect to that on stage 4, but the amount on stage 6 remains less than that on 5, type I is converted into II,. If the amount on stage 6 increases to the same level as that on stage 5, type III is found from II,. Further increase of the amount on stage 6 gives type IV, V and VI consecutively. Otherwise, if in distribution type II, the amount on stage 5 is decreased compared to that on 6 and 4, the type II, and even II, is produced.

VAN CAUWENBERGHE

In Table 6 the PAH are listed with their corresponding distribution type in each sample. From thesedata it follows that: (1) Each compound can follow different distribution types in different samples. Nevertheless, considering S,, S, and S, each PAH seems to follow only on limited number of distribution types always closely related (e.g. I, II,). (2) The S2 winter sample is outstanding both with respect to the measured concentrations as well as to the- distribution shapes. Compared with the other samples, the distribution of PAN clearly shifts to a type with a higher amount on stage 6 (e.g. II, VI). Since the sampling station was situated in a residential area, the enrichment in PAN of the fractions below 0.5pm is explained by the increased emission of condensation aerosol generated by domestic heating in winter. (3) The compounds with lower mol. wt tend to follow a type II,, II,, or II, distribution. Roughly it can be stated that the concentrations reach a constant level in the particle size range below 1.5pm. These compounds are reported to be abundantly present in the gas phase after a filtration sampling unit (Cautreels and Van Cauwenberghe, 1978). As far as these compounds evaporate from the afready collected particles it can be expected that the losses increase with decreasing particle size. From this the hypothesis is formulated that distribution patterns with a nearly constant concentration level for stages 6 to 4 are generated from a general distribution pattern IV, V or VI by blow-off of more volatile compounds. (4) For PAH with higher mol. wt, concentrations increase continuously with decreasing particle size. In most cases there is an important difference between concentrations in the fractions on stage 3 (3-I.5pm) and 4 (l-1Spm). Similar conclusions can be drawn for the nitrogen containing polynuclear aromatic hydr~ar~ns, although concentration levels increase more slowly with decreasing particle size. The increasing ratio ofconcentration in the smallest particle size range (stage 6) to that in the large range (stage 1) with increasing mol. wt, is consistent with the results of de Maio et al. (1966) for some PAH (pyrene, chrysene, benzo(a -te)pyrenes) in the Pittsburgh air. They analysed two fractions of particulate matter, one containing particies larger than 5pm and one with the smaller ones, and found pyrene was distributed about equally over the two fractions, but benzopyrenes were only detected on the smaller particles. 3.2. Percentages found below 3 and 1 pm. Data are given in Table 3 in the second and third column for each sample. The values were obtained graph~aliy from the cumulative mass distribution plots in order to eliminate slight differences in cut-off diameters, due to differences in flow rates. A remarkable agreement exists between the four samples. However, it must be recognised that this interpretation tends to fiatten out somewhat evident differences in distribution shapes.

distribution of organic pollutants

Size

‘2 )Ibenw”fhrot*“e,

-53 i%oroni

hene

i

I

6

Sroge number

Fig. 4_ Typical size disrribut&

curves far the pc@cyelk aromatic hydracarbons

Tabk 6. Distriburwn typesfor PAH

__._^..--_~lll__~_

- _

__

Sample code Polyaromatic

__.

_

hydrocarbon .~.

.- .__

s,

s,

_

phenanthrene canthracene mclhylphenanthrwe mcthytanrbracene

II, 11,

VI

fluoranthene

II,

IV

pyrene benzo(a)fluorene benzo(e)fluotene methylpyrene chrysene + benm(afant

11:

VI

II,

hracene

II, 4 IV

::: IV

4

Vf

I1b

benzo(b + k@xxmthenes benzoofa+ eipyreaes perylene

V IV

VI VI II

o-phcnylencpyrene benzo(ghi)perylene

:I11 Gr *

HE vi

dibenzanthracenes piccne bfmoquinoline + acridine

VI III,

VI VI

14 I&

VI Y1

phenanthridine benzacridine

I1b

dibmzacridine -.-.--

--~

*Intermediatedistribution ) Measured

VI

VI VI

type between II, and II,. for the sum of benzopyreneb aaff perylenc.

VI V V US il, 11, II, -.--

IIh

V VI Y fll, IV II,

-,

2238

L. VANVAECK and K.

In the respirable size fraction, below 3 pm, we found 85-900/, of the aliphatic hydrocarbons (tetracosane and higher homologs). There is no significant COP relation of this quantity with carbon number. The lower compounds, that are aiso found abundantly in the gas phase show some greater variation. Below 1 pm, about 60-70% of the higher alkanes are found. These percentages are nearly constant for all samples. The particles smaller than 3pm contain about 9C-95% of the acids from eicosanoic acid up and somewhat less for the lower homologs. Also, the more irregular behaviour of lower homologs such as myristic acid correlates with the abundancy in the gas phase of this compound. In the size range below 1pm, 70-77x of the acids are found. The PAH present in the winter sample S2 are found to an extent of 95--98x on the respirable size particles ( < 3 pm), while for the three other samples this level is about 90-95%. Nitrogen containing polyaromatic hydrocarbons are also found in significantly greater amounts on the small size particles of the winter sample. The lower mol. wt PAH are less abundant in this fraction. On particles below 1 pm 60-70x of the PAH are found, except in winter where this percentage increases to about 70-80%. In contrast with the aliphatics and carboxylic acids, the PAH content of the fraction below 1 pm can vary significantly in comparison with the fraction below 3 pm : the relative amount on particles below 1 /Irn increases significantly more than on particles below 3ym. As explained before, this reflects the influence of domestic heating, generating condensation aerosol enriched in PAH. Pierce et al. (1975) found a similar relationship winter/summer, although the percentages of PAW on particles in the size range below 3 pm are 20% lower. Kktesz-Saringer (1971) reported for benzo(a)pyrene in a polluted part of Budapest (Hungary) 987; in the range below 3pm in winter and 9OP:, during October-November. It is interesting to compare the percentages found for the range below 3pm in the Wilrijk suburban residential area with these reported by Broddin et ai. (1977) for diluted coke oven emission samples. The winter sample Sr reaches the same percentages as the coke oven sample, while in other periods (autumn and spring) the residential values are a few percent lower. However, absolute concentration levels for PAH were on the average about 50 times higher in the coke oven emission samples. The high concentration levels of the PAH in the winter sample are typical for condensation aerosol produced by incomplete combustion processes, collected shortly after generation. 4. Cumulatioe mass ~isrriburion The cumulative distributions of the individual pallutants were clearly not normal, but in most cases one can draw two straight lines intersecting each other at the central third point. However, in our opinion, neither log-normality nor bimodality of the distri-

VAN CAUWENBERGHE

bution can be proven conclusively, since the impactor gives only 6 fractions. The results show that the mean mass effective diameter (MMED) for the PAH is lower in the winter sample but the (I# remains at the same level, Typical MMED values for the benzopyrenes are 0.58~m (S,), 0.71 pm (S,) and 0.72~m (S,) and the corresponding G@are 2.2, 1.9 and 2.0 respectively. The distribution is not found to be narrower in winter in contrast with the data observed by Pierce et al. (1975). In the series of alkanes and carboxylic acids, the MMED decreases with increasing mol. wt. The CT@ remains at the same level, indicating a shift of the whole distribution to smaller particle size with retention of the same width. The MMED and ug are spread around the same values in all samples. The winter sample does not form an exception for these compounds. The acids are found to have a more narrow distribution than the ahphatics.

CONCLUSlONS

In ambient aerosols of a typical suburban area. the distribution of organic compounds as function of particle size has been determined for about 60 potlutants : aliphatic hydrocarbons (octadecane to dotriacontane), carboxyiic acids (myristic acid to octacosanoic acid), about 20 polynuclear aromatic hydrocarbons (PAH), including the strong carcinogens and some nitrogen~ontaining polyaromatics. Samples were taken with a high volume cascade impactor during autumn, winter and spring. Although TSP as well as concentrations for each compound can vary significantly from one period to another, the relative composition of the samples was found to be similar. In the classes of aiiphatic hydrocarbons, carboxylic acids and PAH, maximum concentrations are found for nonacosane, docosanoic or tricosanoic acid (if palmitic and stearic acid are not considered) and for the carcinogenic benzofluoranthenes, benzopyrenes and ~nzo(ghi)~rylene respectively. For the alkanes with even carbon number,greater concentration levels are found than for these with uneven chain length. For the carboxylic acids, the inverse effect is found. A tentative explanation of this phenomenon for the aikanes is given and related to different increments of the mofar heat of va~risation in the homolog series. Also the lower mol. wt PAH can be- affected by the same evaporation artifact. The distribution patterns have been found to be similar in the classes of the alkanes and carboxylic acids. For the PAH the distributions can be classified according to eight typi~i distributions. In the studied samples, each PAH followed only closely related types. Additionally, in the winter period the distribution shifted toward smaller particles. An indication for evaporation artifact is that the distribution of the more volatile lower molecular weight PAH flattens in the

Size distribution

2239

of organic pollutants

particle size range. More research is needed to investigate the sampling process with respect to the evaporation problem as well as to assess the importance of chemical transformations of the collected matter on the filter during sampling. When the distributions are interpreted in terms of percentages found below 3 and 1 pm, most aliphatic hydrocarbons (SS-900;,) are found on particles below 3 pm (60-70:; below 1 pm). For the carboxylic acids up to 90-957, are found on particles below 3 pm, and 70-77”, below 1pm. These percentages are strongly dependent on the season for PAH as could be expected : 95-98”,, of the PAH below 3 pm in the winter and 9t-95y10 in the other periods. The fraction below 1 pm is found to contain 70-80% of the PAH in the winter, and lOY, less in the other samples. The cumulative mass distribution of the total suspended matter can be of a log-normal type, the cumulative mass distribution of the individual pallutants cannot. However, for the Hi-Vol cascade impactor the low number of fractions does not allow serious tests for log-normality. It is interesting to add an evaluation of the health hazards to these conclusions, since the fraction between 3 and 0.5 pm is largely retained in the respiratory tract. With a normal respiring rhythm, a man can be expected to sample 1000m3 air in about 3 months. Over that period in Belgium the human pulmonary system will be exposed to about 5-1Opg aliphatics and carboxylic acids, and up to 15 pg of polyaromatics in the size range of 3-0.5 pm. During winter periods, the amounts of PAH will increase five fold up to 50-6Opg in the case of carcinogenic compounds such as benzofluoranthenes and benzopyrenes.

REFERENCES

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Acknowledgements - The National ‘Foundation of Scientific Research (NFWO) is thanked for according a grant to L. Van Vaeck as “aspirant-navorser”.

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7, 319-322.

Dams R. (1974) Study of the inorganic composition of atmospheric aerosols. AggregaatsthesisState University Ghent, Belgium. de Maio L. and Corn M. (1966) Polynuclear aromatic hydrocarbons associated with particulates in Pittsburgh air. J. Air Polfur. Control Ass. 16, 67-71. Kertlsz-Sbringer M., Mtszaros E. and Varkonyi T. (1971)On the size distribution of benzo(a)pyrene containing particles in urban air. Armospheric Enrironment 5, 429-431. Lippmann M. (1970) Respirabledust sampling. Am. Id. Hyg. Ass. J. 31, 138-159. Lundgren D. A. and Paulus H. J. (1975)The mass distribution of large atmospheric pollutants. J. Air Pollur. Control Ass. 25, 1227-1231. Pierce R. C. and Katz M. (1975) Dependency of polynuclear aromatic hydrocarbon content on size distribution of atmospheric aerosols. Encir. Sci. Technol. 9. 347-353. Van Vaeck L. and Van Cauwenberghe K. (1977) On the evaluation of accuracy in quantitative multiple ion detection monitoring gas chromatography-mass spectrometry with electron impact ionization. AM/U. Lerr. 10,467-482.

Van Vaeck L., Broddin G.. Cautreels W. and Van Cauwenberghe K. (1978) Aerosol collection by cascade impaction and filtration: influence of different sampling systems on the measured organic pollutant levels. Sci. Tar. Envir. (in press). Whitby K. T.. Charlson R. E.. Wilson W. E. and Stevens R. K. (1974) The size of suspended particulate matter in air. Science 183, 1098-1150. Willeke K. (1975) Performance of the slotted impactor. Am, Id. Hyg. Ass. J. 36, 683-691.