Characterization of organic species associated with indoor aerosol particles

Environment International, Vol. 12, pp. 93-97, 1986

0160-4120/86 $3.00 + .00 Copyright©1986PergamonJournals Ltd.

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CHARACTERIZATION OF ORGANIC SPECIES ASSOCIATED WITH INDOOR AEROSOL PARTICLES Charles J. Weschler and Karen L. Fong a Bell Communications Research, 331 Newman Springs Road, Red Bank, NJ 07701 (Received 26 February 1985; Accepted 30 August 1985)

Automatic dichotomous samplers were used to collect fine and coarse particles inside office buildings located in the central region of the United States. Outdoor samples were collected at the same time. Following collection, samples were analyzed for both nonpolar organic compoundsand fatty acids. The former were characterized by therrnal-desorption--gas-chromatographic--mass-spectrometricprocedunes. The latter were solvent extracted, methylated, and identified by gas chromatography--massspectrometry. The nonpolar compounds associated with the indoor particles include n-alkanes; branched alkanes; phthalate, phosphate, and azelate esters; chlorofluorocarbonsand nicotine. Typical concentrations for nonpolar organic constituents of indoor particles are much higher than for those of outdoor particles. The major fatty acids associated with the indoor particles were palmitic, stearic, and myristic. Higher molecular weight fatty acids, primarily even carbon number species, were also present. Most of the fatty acids associated with indoor particles are due to infiltration of particles from outdoors.

Introduction

cles can cause opens on contacts and connectors. Carbon fibers are good conductors and can cause shorts leading to malfunctions or even destruction o f electronic equipment ( N A S A , 1978). Organic c o m p o u n d s can contribute to the failure o f devices by promoting contact activation which leads to the erosion of the contact surface (Gray et al., 1977). Silicone fluids emitted by certain photocopiers have been implicated in numerous failures of electronic equipment (Kitchen and Russell, 1975; Reagor and Russell, 1985). Organic compounds can absorb, polymerize, and form resistive films on precious metal contacts and connectors (Hermance and Egan, 1958; Sharma and Dasgupta, 1983). Certain organic compounds can contribute to head crashes in the highspeed disc drives found in current m e m o r y units. Clearly, organic c o m p o u n d s associated with particles can affect not only people but also their technology. In this study, gas c h r o m a t o g r a p h y - - m a s s spectrometry (GC/MS) has been used to analyze the organic constituents o f fine and coarse airborne particles collected outdoors and indoors at telephone office sites located in the central region o f the United States. The nonpolar organic c o m p o u n d s were characterized by a thermal desorption procedure, while fatty acids were identified using a methylation technique.

Chemicals found in indoor air, both in the vapor phase and associated with airborne particles, can have a significant impact on materials. Rice et al. (1980) have examined the indoor corrosion rates o f various metals at several locations in the United States. They observed that relative humidity, reduced sulfur gases, and chlorine containing gases can significantly influence the rates. Elevated concentrations o f ozone within a building can crack rubber and certain polymers used in equipment. H e r m a n c e et al. (1971) have demonstrated that high levels of airborne nitrate cause electrolytic stress corrosion cracking o f nickel brass wire springs supporting the contacts on relays in Los Angeles switching offices. Water soluble ionic species accumulated on electronic equipment such as connectors, printed wiring boards, and backplanes can contribute to current leakage that m a y ultimately lead to circuit failure. Trace amounts o f ionic species can produce unintended inversion layers in V L S I devices (Sinclair and Psota-Kelty, 1984). Classical chemical, electrochemical, and galvanic corrosion processes can be induced or assisted by ionic contamination. PartiaSummer research student, University of Texas at E1 Paso. 93

94

Experimental Sampling The sampling procedure has been previously described (Weschler et al., 1983; Weschler, 1984). Briefly, automatic dichotomous samplers were used to collect fine (smaller than 2.5 ttmdiam.) and coarse (between 2.5 and 15 )xm diam.) airborne particles. The particles were collected on Teflon membrane filters that had been precleaned using ultrasonic extract i o n s - f i r s t with water, then with methanol. Two typical buildings were selected as test sites. The first test series was conducted in Wichita, KS, during the fall and early winter of 1981-1982. The second series of tests was conducted in Lubbock, TX, during the late winter and spring of 1982. At each location, the outdoor sampler was located on the roof (approximately 6 m above ground). Samplers were run continuously, with two outdoor samples collected for every indoor sample.

Equipment and Materials Organic compounds were separated and identified with a Hewlett-Packard 5992A gas chromatograph-mass spectrometer (GC-MS). The GC oven contained a 0.2 × 120 cm glass column packed with 3% OV101 on 100-120 mesh Chromosorb W-HP and was programmed to rise from 50 or 100 °C to 220 °C at a rate of 4 °C/rain. The injection port was held at 240 °C, and the helium carrier gas flow was maintained at 20 mL/min. The response of the mass spectrometer was calibrated periodically with squalene, n-alkane, and fatty acid methyl ester standards. Samples were quantified by comparison of peak areas with those of the standards. The BF3-methanol reagent was obtained from Supelco, Inc. in sealed glass ampules (2-mL aliquots) and was refrigerated prior to use. Authentic compounds used to confirm GC/MS analyses were obtained from Aldrich Chemical Co. and Supelco, Inc. The thermal desorption procedures were performed using a Chemical Data Systems "Pyroprobe 100" interfaced to the GC/MS; the thermal interface was held at 150 °C.

Thermal Desorption Procedure The thermal desorption procedure, as applied to nonpolar organic constituents of aerosol particles, has been recently outlined (Weschler, 1984). To summarize, a typical analysis began by adding a known quantity of squalene or docosane (internal standards) to a loaded Teflon membrane filter. The spiked filter was placed in a quartz tube that, in turn, was placed in a coiled heating element. The heating element was sealed in an interface that was attached to the gas chromatograph and through which helium carrier gas was flowing. The run was initiated by heating the quartz tube to 250 °C for 20 sec. The helium carrier

Charles J. Weschlerand KarenL. Fong gas purged the volatilized organics from the filter into the gas chromatograph--mass spectrometer. Within the accuracy of the system (approximately 10~/0) the recoveries of various hydrocarbons were indistinguishable from those obtained using a toluene extraction procedure. For organic compounds that do not have to be derivatized to be identified, thermal desorption yields results comparable to solvent extraction, is faster, and is less likely to introduce contaminants or artifacts. Blanks were obtained by analyzing unexposed filters and contained only trace amounts of n-alkanes from C17 to C26 (typically less than 10% of the nalkanes detected outdoors in this study). The n-alkalines displayed no odd/even preference. All data are blank corrected.

Methylation Procedure Fatty acids associated with the samples were characterized with the aid of an esterification procedure. In a typical analysis a loaded Teflon membrane filter was separated from its polypropylene backing, placed in a 5 rnL reaction vessel along with 2.0 mL of petroleum ether, and ultrasonically agitated for 30 rain. After removing the extracted filter, 2.0 mL of a 12% (W/W) BF3-methanol solution were added to the reaction vessel which was then sealed and boiled in a water bath for 10 min, The reaction was quenched by injecting 1 mL of distilled water. After an additional 15 min, the petroleum ether layer (top layer) containing the methyl esters was removed. (Care must be taken to exclude the acidic aqueous layer that could hydrolyze the column packing.) 1.0 p,L of the internal standard (1.0 ~g/p,L of squalene in toluene) was added to the petroleum ether layer that was then evaporated almost to dryness under reduced pressure at room temperature. The residue was redissolved in about 5 ~L of methanol and this entire solution was injected into the GC/MS. Several filters, already extracted as described, were reextracted with an additional 2.0 mL of petroleum ether. These second extracts were then methylated using the previously outlined procedure. Methyl palmitate and methyl stearate (see Results and Discussion section below) were the only esters detected in these repeat extractions/methylations, and their abundances were typically between 4% and 7% of those determined in the initial extraction/methylation. In other words, the extraction efficiency is typically between 93% and 96%. Several field samples with expected low levels of fatty acids were spiked with 1.0 )xL of a myristic acid solution (1.35 p,g/ttL of petroleum ether) prior to extraction and methylation. Using the procedures outlined above, the methyl myristate " r e c o v e r e d " typically ranged between 85% and 90% of the theoretical value, although a recovery as low as 56% was observed. Possible losses include incomplete parti-

Indoor aerosol particles

95

tioning, incomplete r e c o v e r y o f the petroleum ether layer, and volatilization during the evaporation o f the p e t r o l e u m ether. Methyl palmitate and methyl stearate were the only methyl esters detected in extractions/methylations of blank filters. The amounts were typically less than the uncertainty in the field data, and the fatty acid data are therefore not blank corrected.

Results and Discussion

Nonpolar compounds The average indoor concentrations and indoor/outdoor ratios for nonpolar organic c o m p o u n d s associated with airborne particles collected at the Wichita and L u b b o c k sites have been recently reported and discussed (Weschler, 1984). At these sites, both the n u m b e r and concentration o f nonpolar organic c o m pounds associated with indoor particles are m u c h greater than those associated with outdoor particles. Table 1 s u m m a r i z e s the indoor and outdoor concentrations for the m o r e abundant indoor species (arbitrary cutoff at 4 ng/m3). The nonpolar c o m p o u n d s associated with the indoor particles include n-alkanes; branched alkanes; phthalate, phosphate, and azelate esters; chlorofluorocarbon lubricants; and nicotine (these last two are not included in Table 1 because o f their low concentrations). C o m p a r i s o n o f organic c o m p o u n d concentrations indoors and outdoors has provided insight concerning the sources o f the various organic c o m p o u n d s . With the exception o f a few nTable 1. Average indoor and outdoor concentrations for major nonpolar organic compounds associated with airborne particles at Wichita and Lubbock.

alkanes, each o f the detected nonpolar organic compounds c o m e s primarily f r o m indoor sources. For selected nonpolar c o m p o u n d s detected indoors, the ratios o f their fine/coarse abundances are more than a factor o f 10 greater than the fine/coarse mass ratio for the c o m p a r a b l e indoor particulate matter. This suggests that these compounds are primarily adsorbed on the surface o f indoor airborne particles, since the surface area o f fine m o d e particles is roughly an order o f magnitude greater than that o f coarse m o d e particles. Further comparisons indicate that adsorption o f nonpolar organic c o m p o u n d s on the surface o f airb o r n e particles is m o r e significant indoors than outdoors, and it is m o s t important for those c o m p o u n d s that have large indoor sources.

Fatty acids Table 2 lists the average indoor concentrations for fatty acids detected in samples f r o m both Wichita and L u b b o c k , as well as average outdoor concentrations for these fatty acids. Abietic acid is the only organic acid detected indoors, but not outdoors. This c o m pound is a m a j o r ingredient of rosin flux and is consistent with soldering activity in both buildings. Typical concentrations for fatty acid constituents o f indoor particles are c o m p a r a b l e to or lower than those of outdoor particles. With the exception o f abietic acid, the fatty acids identified in the samples are those expected f r o m vascular plant waxes (Tulloch, 1976). The greater concentrations of even carbon n u m b e r species than of odd Table 2. Average indoor and outdoor concentrations for fatty acids associated with airborne particles at Wichita and Lubbock. Indoor

Indoor Outdoor

Compound n-Hexacosane n-Heptacosane n-Octacosane n-Nonacosane n-Triacontane n-Hentriacontane Branched triacontane

Concentrationa (ng/m3) Concentrationa, b Wichita Lubbock (ng/m~) 7 40 10 40 30 140 30

6 20 5 25 15 100 20

Branched hentriacontane

75

55

c

Butylbenzyl phthaiate Di(2-ethylhexyl)phthaiat¢ Dinonyl phthalate

20 55

1 20

c 2

15 20 4 6 8 30

15 20 25 c I0 15

c c c c c c

Didecyl phthalate Tris(butoxyethyl)phosphate Tris(2-ethylhexyl)phosphate Bis(2-ethylhexyD azelate Nonylphenol isomers

1.8 2.7 2.4 5.1 1.1 2.7 c

30070standard deviation (n = 6). bAverage of outdoor concentrations at Wichita and Lubbock. cCompound not detected. a.4.

Compound Lauric acid Tridecanoic acid Myristic acid Pentadecanoic acid Paimitic acid Heptadecanoic acid Oleic acid Stearic acid Nonadecanoic acid Arachidic acid Heneicosanoic acid Behenic acid Tricosanoic acid Lignoceric acid Pentacosanoic acid Hexacosanoic acid Abietic acid

Concentrationa (ng/m3) Wichita Lubbock 1.5 0.5 6

c c 0.5

Outdoor Concentrationa, b (ng/m3) 2 0.2 11

2

0.1

6

50 3 3.5

8 0.1 0.2

120 3

45

5

2 lI 6 13 5.5 6.5 I l 0. I

c c c 0.3 c c c c 0.3

8 54

0.9 3 0.6 3.5 0.5 3 0.3 1.5 c

a.a. 50070 standard deviation (n = 5). bAverage of outdoor concentrations at Wichita and Lubbock. cCompound not detected.

96

Charles J. Weschlerand Karen L. Fong

carbon number species is further confirmation o f a vegetative source. Typical indoor/outdoor ratios for the concentrations o f fatty acids are between 0.2 and 4. These ratios indicate that a large percentage o f the fatty acids enter from outdoors, and, unlike the situation for nonpolar organic compounds, indoor sources are often insignificant. The higher indoor concentrations at Wichita compared to L u b b o c k reflect the greater penetration o f outdoor particles at the former office compared to the latter (see below). The concentrations reported in Tables 1 and 2 are total concentrations. However, fine and coarse mode concentration data exist for each o f the organic species listed, and such data can reveal the manner in which an organic c o m p o u n d is associated with airborne particles. For selected nonpolar compounds detected indoors, the ratios of their fine/coarse abundances scale with the ratio o f the fine/coarse surface area, not the ratio o f the fine/coarse mass. This suggests that these compounds are primarily adsorbed on the surface of indoor airborne particles (see above). Conversely, for the fatty acids (see Table 3) the ratios of their fine/ coarse abundances are close to the fine/coarse mass ratio, which suggests that these compounds are integrally associated with the airborne particles (i.e., these compounds occur throughout the particles, rather than just on particle surfaces). Comparisons The indoor particles at the Wichita and Lubbock sites contain certain nonpolar organic compounds whose concentrations are determined almost exclusively by indoor sources. At the other extreme, these indoor particles contain fatty acids whose concentrations are determined primarily by the infiltration o f outdoor species. It is interesting to examine how the indoor concentrations of these two different types o f c o m p o u n d s - - t h o s e with indoor sources and those with outdoor s o u r c e s - - a r e affected by the substantially different air handling systems at the Wichita and Lubbock sites, The Wichita office does not prefilter the makeup air and uses low efficiency filters in the air

Table 3. Fine and coarse mode concentrations for selected fatty acids both indoors and outdoors at Lubbock (29 April 1982-6 May 1982). Compound

Airborne particles Outdoor Indoor

Fine (ng/m~) 41,900 2,700

Coarse(ng/m~) 40,900 1,100

Ratio of Fine/Coarse

1.0 2.4

Palmitic acid Outdoor Indoor

17.2 4.5

51.5 5.2

0.33 0.86

stearic acid Outdoor Indoor

21.9 3.9

40.6 1.9

0.53 2.0

handling plenum, while the Lubbock office prefilters the makeup air with medium efficiency filters and uses high efficiency filters in the air handling plenum (Weschler et al., 1983). Eight out o f 15 compounds in Table 1 have indoor concentrations that are between 1.4 and 2 times larger at Wichita than at Lubbock. The evidence suggests that a high percentage o f these nonpolar compounds are adsorbed on the surface of the airborne particles (Weschler, 1984). The magnitude o f these concentration differences between Wichita and Lubbock is consistent with such a mechanism. The surface area o f indoor airborne particles per unit volume of air is roughly 1.5 times as great at Wichita as at Lubbock. Unfortunately, the indoor concentrations o f fatty acids at L u b b o c k were frequently beneath the limit o f detection. In those situations where meaningful measurements were possible (myristic, palmitic, and stearic acid), the indoor concentrations were from 6 to 12 times larger at Wichita than at Lubbock (Table 2). This large difference (significantly greater than the factors o f 1.4 to 2.0 observed for selected nonpolar species) is a consequence o f the more efficient building filtration system at Lubbock, since the indoor concentrations of fatty acids is due chiefly to the infiltration of outdoor particles. Indeed this large difference is an additional argument suggesting that vapor phase/particle surface partitioning is relatively unimportant for these fatty acids. If there was a significant outdoor vapor phase component, building filters would have little effect on its infiltration. Such vapors would then reequilibrate with the surface of indoor airborne particles, and the difference between Wichita and L u b b o c k (indoor fatty acid concentrations) would be considerably less than observed. To recapituate, Lubbock has a more efficient building filtration system than Wichita. The concentration of organic compounds with dominant indoor sources will be less at Lubbock, to the extent that the surface area o f indoor airborne particles per unit volume of air is less. This assumes significant vapor phase/particle surface partitioning for such compounds. The concentration o f organic compounds with dominant outdoor sources will be less at Lubbock, to the extent that outdoor particles infiltrate less. This assumes negligible vapor phase/particle surface partitioning for such compounds. The effect o f filtration systems is more pronounced in the second situation, where the organic compounds are integrally associated with particles, than in the first situation, where the organic compounds are distributed between the vapor phase and particle surfaces.

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Indoor aerosol particles Gray, E. W., Uhrig, T. A., and Hohnstreiter, G. F. (1977) Arc durations as a function of contact metal and exposure to organic contaminants. J. Appl. Phys. 48, 104-109. Hermance, H. W. and Egan, T. F. (1958) Organic deposits on precious metal contacts. Bell System Tech. J. 37, 739-777. Hermance, H. W., Russell, C. A., Bauer, E. J., Egan, T. F., and Wadlow, H. V. (1971) Relation of airborne nitrate to telephone equipment damage, Environ. Sci. Technol. 5, 781-785. Kitchen, N. M. and Russell, C. A. (1975) Silicone oils on electrical contacts--Effects, sources, and countermeasures. Proceedings of the Twenty-First Annual Holm Seminar on Electrical Contacts, Chicago, IL. National Aeronautical and Space Administration (1978) Carbon fiber study. Technical Memorandum 78718, NASA. NASA Langley Research Center, Hampton, Virginia. Reagor, B. T. and Russell, C. A. (1985) A survey of problems in telecommunication equipment resulting from chemical contamination. Proceedings IEEE Holm Seminar on Electrical Contact Phenomena, Chicago, IL. Rice, D. W., Cappell, R. J., Kinsolving, W., and Laskowski, J. J.

97 (1980) Indoor corrosion of metals, J. Electrochem. Soc. 127, 891-901. Sharma, S. P. and Dasgupta, S. (1983) Reaction of contact materials with vapors emanating from connector products, IEEE Trans., CHMT-6 553-559. Sinclair, J. D. and Psota-Kelty, L. A. (1984) Ionic substances on electronic equipment: amounts, sources and effects, in Proceedings of International Congress on Metallic Corrosion, Vol. 2, pp. 296-303, National Research Council of Canada, Ottawa. Tulloch, A. P. (1976) In Chemistry and Biochemistry o f Natural Waxes, P. E. Kolattukudy, Ed., pp. 236-252, Elsevier, New York, NY. Weschler, C. J. (1980) Characterization of selected organics in sizefractionated indoor aerosols, Environ. Sci. TechnoL 14 428-431. Weschler, C. J,, Kelty, S. P., and Linguosky, J. E. (1983) The effect of building fan operation on indoor-outdoor dust relationships, J. Air Pollut. Control Assoc. 33, 624-629. Weschler, C. J. (1984) Indoor-outdoor relationships for nonpolar organic constituents of aerosol particles, Environ. Sci. Technol. 18, 648-652.