Effects of Ambient Temperature on Aspects of Airborne Polycyclic Aromatic Hydrocarbons Hlroyasu Yamasakl, * Kazuhlro Kuwata, and Hlroko Mlyamoto
Environmental Pollution Control Center, 62-3,1 Chome, Nakamichi, Higashinari-ku, Osaka City, 537, Japan ~~~
~
Three- to six-ring polycyclic aromatic hydrocarbons in the vapor phase (PAHs,,,) and in the particulate phase (PAHs,,) and total suspended particulate (TSP) in ambient air were sampled and determined year-round. At ambient temperature levels, substantial amounts of threeto five-ring PAHs were found in the vapor phase depending upon temperature (T, K) and the six-ring PAHs were all found in the particulate phase. For three- to five-ring PAHs, the Langmuir adsorption concept was introduced for PAHs,,~,and PAH$,t on the particulates. log [(PAHs,ap)/{(PAHs,at)/(TSP))] was related to 1/T, and a high correlation (r = -0.834 to -0.942) was obtained between the two quantities. Thus, aspects of the three- to five-ring PAHs in ambient air were considered to be explained by using the Langmuir adsorption concept. Introduction Polycyclic aromatic hydrocarbons (PAHs) have received much attention in studies of air pollution because some of these compounds are highly carcinogenic. In most cases, PAHs in the atmosphere have been collected as particulate matter on glass-fiber filters (GFs) by using conventional high-volume air samplers. However, as pointed out in several articles (1-4),three- to five-ring PAHs are found, or estimated to be to some extent, in the vapor phase at ambient temperature. Especially the three- and four-ring PAHs, which have relatively high vapor pressures, are not satisfactorily trapped on GFs. Some authors ( I , 2) report that even benzopyrene, which has a low vapor pressure, is appreciably lost on a GF by sublimation and/or decomposition during ordinary sampling. The degree of loss seems to depend greatly upon the sampling temperature. In a previous study (3),we reported that three- to five-ring PAHs in the vapor phase can be effectively trapped on polyurethane foam plugs (PUFPs) and that a high volume of urban air can be sampled for simultaneous determination of three- to six-ring PAHs by using a combination of a GF and PUFPs attached to a high-volume air sampler. From the results, substantial amounts of three- to five-ring PAHs are found in the vapor phase. The facts mentioned above suggest that it is important to investigate the state of the PAHs in the atmosphere in studies of air pollution. So far, few reports have been published concerning the determination of various PAHs in the vapor phase and in the particulate phase in urban air throughout the year. In this study, urban air was sampled throughout 1 year by using the apparatus previously reported (3), and the various PAHs in the vapor phase and in the particulate phase 0013-936X/82/0916-0189$01.25/0
were determined. Aspects of PAHs in ambient air are explained by using the Langmuir isothermal adsorption concept. Experimental Section Reagents and Materials. The PAHs as standard reagents were purchased from Wako Pure Chemical Industries (Osaka, Japan), Tokyo Kasei Kogyo (Tokyo, Japan), R. K. Chemical (Hartville, OH) and Analabs (North Haven, CT). Benzene and n-hexane were pesticide-residue-analysis grade from Wako Pure Chemical Industries, and other solvents were either chromatographic or spectral grade from Wako Pure Chemical Industries. Davison Chemical No. 923 silica gel (Fuji Davison Chemical, Aichi, Japan) for a purification column (20 cm X 10-mm i.d., glass) was washed with benzene for 10 h in a Soxhlet extractor and activated by heating at 140 "C for 4 h. The PUFP (5 X 10 cm, 0.021 g/cm3 density) was cut out from a polyurethane foam sheet (ether type) available from Bridge Stone Co. Inc. (Tokyo, Japan) and washed with acetone for 10 h in a Soxhlet extractor followed by similar washing with cyclohexane for 10 h. The GF was a Toyo Roshi (Tokyo, Japan) GB-100R which could trap 99.99% of 0.3-pm particulate matter. The GF was heated at 350 "C before use to eliminate organic compounds. Apparatus. The sampling apparatus for PAHs is shown in Figure 1. The apparatus was attached to a conventional high-volume air sampler. An Ogasawara Instrument Manufacturing Co. Ltd. (Tokyo, Japan) A-1250 automatic recording thermometer with a platinum thermosensor, which was set next to the sampling apparatus, was used. A Shimazu-LKB (Shimazu Co., Kyoto, Japan) 9OOO combined gas chromatograph-mass spectrometer was used to identify the PAHs. A Varian (Walnut Creek, CA) 2100 gas chromatograph with a flame ionization detector was used to determine quantitatively the PAHs identified. The working conditions were as follows: column, 1.5 m X 2-mm i.d. stainless-steel tube packed with 6% Dexil300 on 80-100 mesh Chromosorb W (HP); carrier gas, nitrogen 30 mL/min; injection temperature, 270 "C; column temperature, isothermal at 160 "C for first 2 min (when amounts of phenanthrene + anthracene are less, isothermal at 140 "C for first 10 min), programmed from 160 (or 140) to 320 "C at 6 "C/min; detector temperature, 350 OC; sample volume, 10 pL. Sampling. Urban air was sampled at 0.75-0.80 m3/min (30.6-32.6 cm/s of linear velocity on the GF) for 24 h (from 10 a.m. through 10 a.m. of the next day) by using the apparatus shown in Figure 1. Suspended particulate was
0 1982 American Chemical Society
Environ. Sci. Technol., Vol. 16, No. 4, 1982 189
Table I. Recovery of t h e PAHs from the PUFP and the G F PUFP PAH anthracene fluorant hene pyrene chrysene benzo[a]pyrene o-phenylenepyrene benzo [ghilperylene
" Averaged value in 5 runs.
PAH PAH found t SD," added, pg I.rg 15.0 10.7 i 0.51 15.0 12.5 i 0.43 15.0 12.4 t 0.30 15.0 12.5 t 0.32 15.0 12.1 t 0.41 15.0 12.7 f 0.54 15.0 12.8 i 0.60
SD = standard deviation.
GF :ecovery,b %
1
PAH found Pg
i
SD," recovery,b %
71.3 (4.8) 83.3 (3.4) 82.7 (2.4) 83.3 (2.6) 80.7 (3.4) 84.7 (4.3) 85.3 (4.7)
11.9 t 0.56 79.3 (4.7) 13.6 t 0.37 90.7 (2.7) 13.7 t 0.24 91.3 (1.8) 13.8 t 0.61 92.0 (4.4) 13.1 t 0.54 87.3 (4.1) 13.6 t 0.42 90.7 (3.1) 13.5 i 0.47 90.0 (3.5) Relative standard deviation (%) is given in parentheses.
$*IR
Table 11. Minimum Detectable Concentrations of the PAHs in t h e Vapor Phase and in the Particulate Phase minimum detectable concn of PXH,b ng m3 vapor particulate PAH" phase phase Ph - An 0.02 0.02 MePh MeAn 0.02 0.02 FI 0.01 0.01 0.01 0.01 PY BaFlren + BbFlren 0.02 0.02 Ch BaAn + tri-Pheny 0.03 0.01 BFlran 0.0Y 0.01 BaP t BeP 0.05' 0.01 o-PhenyPy 0.05' 0.02 BghiPery + Anthan 0.05' 0.02 Ph + An: phenanthrene - anthracene. MePh + MeAn: methylphenanthrene + methylanthracene. FI: fluoranthene. Py : pyrene. BaFlren iBbFlren: benzo[a]fluorene + benzo[h ]fluorene. Ch - BaAn T tri-Pheny: chrysene - benzo[a]anthracene t triphenylene. BFlran: benzofluoranthene. BaP + BeP: benzo[a Ipyrene T benzo[e]pyrene. o-PhenyPy: o-phenylenepyrene. BghiPery Anthan: benzo[ghi]perylene t anthanthrene. Concentration calculated from 1100 m 3 of an air sample. The minimum detectable concentrations in the vapor phase were higher than those in the particulate phase because of background peaks extracted from the PUFP.
-
Flgure 1. Sampling apparatus for atmospherlc PAHs: (A) OF, (8) stainless-steel net, (C) Teflon gasket, (D,) first PUFP, (D2)second PUFP, (E) stalnless-steel cylinder.
simultaneously collected by an ordinary high-volume air sampler. The averaged temperature was calculated from the temperature continuously recorded throughout the day by a thermometer. The sampling was carried out every 2 weeks from November 1977 through November 1978 on the roof of the Environmental Pollution Control Center. Analytical Procedure. (1)(i) Extract the GF with 100 mL of cyclohexane for 6 h in a Soxhlet extractor. (ii) Extract the individual PUFPs with 300 mL of cyclohexane in a similar way. (2) Evaporte the individual extracts to 3 mL. (3) Extract 3 times with 3 mL of dimethyl sulfoxide (Me2SO)and combine the extracts. (4) Add 9 mL of water to the MezSO extract. (5) Extract 3 times with 3 mL of cyclohexane and combine the extracts. (6) Wash with 1 mL of water. (7) Evaporate to 1mL. (8) Chromatograph the sample with the silica gel column (20 cm X 10-mm i.d.); elute with 50 mL of hexane and discard the eluent; and then elute with 50 mL of 3:2 hexane/benzene and remove the eluent. (9) Evaporate the eluent to 0.5 mL. (10) Identify PAHs by gas chromatography-mass spectrometry. (11)Quantitatively determine the PAHs by gas chromatography with a flame ionization detector.
Results and Discussion Isomers of PAHs, which were difficult to separate by gas chromatography and which were of identical quality, were presented as the total amount or total concentration of the isomers, and one of the isomers was used as a standard because of their identical responses to the flame ionization detector (5). Concentrations of a PAH in the vapor phase (PAH,,,,) and in the particulate phase (PAH,,,,) were calculated from the amount of the compound trapped on 190 Envlron. Scl. Technol., Vol. 16, No. 4, 1982
the PUFPs and on the GF, respectively. Several unknown contaminants extracted from the PUFPs were effectively eliminated through the extraction procedure and the column chromatography so that effects of organic compounds other than PAHs were minimized. Table I indicates the recoveries of the PAHs placed on the PUFP and on the GF via the analytical procedure wherein 15 pg of the individual PAHs were used. A minor loss of the three-ring PAH (anthracene) was observed. The loss of the PAHs tended to be slightly higher on the PUFP than on the GF. Generally, reasonable recoveries were obtained for the three- to six-ring PAHs. At these levels, the PAHs could be determined with less than 5% relative standard deviations. Table I1 indicates the detection limits of the PAHs through the analytical procedure in which the relative standard deviations were less than 15%. Table 111 indicates the percentage of the PAHs trapped on theatwo PUFPs and on the GF from urban air in the range 4.9-29.8 "C of averaged sampling temperature. The three-ring PAHs seemed to be in the vapor phase for the most part at the ambient temperature. At temperatures higher than 25 "C, the amount of phenanthrene anthracene found on the second PUFP often exceeded a half of that on the first PUFP. If the compounds are partitioned between the gas phase and the PUFP phase just as in gas chromatography and if their distribution in the front part of the
+
Table 111. Percentages of the PAHs Trapped on the First PUFP, o n the Second PUFP, and o n the GF % of the PAHs on the trapb second PUFP GF first PUFP minC
PAH' Ph + An MePh + MeAn F1 PY BaFlren + BbFlren Ch + BaAn + tri-Pheny BFlran BaP + BeP o-PhenyPy BghiPery + Anthan
42.4 66.4 16.7 70.8 48.2 6.3
ndf ndf ndf ndf
maxd 97.1 98.7 98.6 98.0 91.6 85.9 43.1 19.9
ndf ndf
a+ 17.0 89.5 90.8 88.5 19.6 38.3 7.8 2.8
ndf ndf
mine
maxd
ave
minC
maxd
ave
0.5 ndf 0.2 0.2
57.3 33.1 1.3 1.5
22.1 8.4 0.6 0.6
ndf ndf ndf ndf ndf ndf
ndf ndf ndf ndf ndf ndf
ndf ndf ndf ndf ndf ndf
0.19 0.48 0.91 1.21 2.54 13.6 56.8 80.1
3.16 6.12 23.4 28.6 51.6 93.1
0.96 2.10 8.55 10.9 20.4 61.6 92.1 91.2
100' 1oog
100'
loop
1OOg
100g
For abbreviations of the PAHs, see Table 11. Number of samples: 28; see Table IV. maximum. e av = average, f nd = not detectable. g PAH found in particulate only.
1008 100g
min = minimum.
max =
T . 'K 313
303
293
3.3
3.L
283
0 I
c
0
a I
-2 10-1 -. a 0
> I
II
Q
Q
10-2 c
10-3 3.1
3.2
3.5
1 6
1 1 ~ ~ 1 0 '3~. - 1
10
0
10
+
Flgure 3. (PAH )(/PAH), vs. l/Tfor BaP and BaP BeP: (0)(BaP 4- BeP),,/(BaP? BeP), obtained in this investigation, (0)BaPVap/ BaP, calculated from the data of Wiest and Rondla (2).
20
TIME I N MINUTES Flgure 2. Typical chromatograms of PAHs trapped on the GF, on the first PUFP, and on the second PUFP from the amblent air. Peak identity: (1) Ph An, (2) MePh MeAn, (3)FI, (4) Py, (5) BaFlren BbFlren, (6) Ch BaAn trCPheny, (7) unknown from the PUFPs, (8) BFlran, (9) BaP BeP, (IO) ndotrlacontane (internal standard), (11) o-PhenyPy, (12) BghiPery Anthan. For abbreviations of the PAHs, see Table 11.
+ + +
+
+
+
+
PUFP is subject to a normal distribution (6),the collection efficiency of the compounds on the PUFPs would be lower than 90% in this case. The other PAHs were efficiently trapped on the PUFPs and/or on the GF. Figure 2 shows typical chromatograms of various PAHs trapped on the PUFPs and the GF from the urban air. Table IV indicates the determined values for PAH,,, PAH,,,,, and total suspended particulate (TSP) in urban air throughout the year. Substantial amounts of the threeto five-ring PAHs were found in the vapor phase depending upon the sample temperature. The sk-ring PAHs, o-phenylenepyrene and benzo[ghi]perylene + anthanthrene, were all found in the particulate phase at any ambient temperature. The ratios of the several PAHs in the vapor phase to those in the particulate phase
(PAH,va,/PAHxpat)obtained here seemed to be in reasonable agreement with the results determined under limited sampling conditions by Cautreels and Cauwenberghe ( I ) . Wiest and Rondia (2)discuss the dependence of atmospheric benzo[a]pyrene (BaP) upon temperature. In their study, the distribution ratio of BaP between the vapor phase and the particulate phase (BaP, /BaP,,J can be calculated from the loss of BaP on the 6F caused by the difference of sampling temperature. Figure 3 shows the ratios of (Bap + benzo[e]pyrene (BeP)),, to (BaP + BeP) obtained here and the ratios of BaP,, to BaP,, lest and Rondia. The former ratios were somewhat by wp" lower than the latter ones at the same temperature levels. Two reasons may be considered. One reason is that the former BaP + BeP vapors were directly trapped and determined while the latter BaP vapors, for which concentrations were apparent values calculated from the loss of BaP on the GF, may contain BaP that was subject to decomposition by oxidation during the sampling as described by Peters and Seifert (7). Another reason may be the different sampling apparatuses. The above results suggest that aspects of the three- to five-ring PAHs in the atmosphere should be more closely related to temperature and concentration of TSP. Since the PAHs may be assumed to be physically adsorbed on particulate surfaces as described by a few authors (4,8), an equilibrium would be established between PAH, and PAH,, at a given temperature in the ambient air. f?hus, the Langmuir adsorption concept may be applied to exEnviron. Sci. Technol., Vol. 16, No. 4, 1982
191
8 a,
192
Environ. Sci. Technol., Vol. 16, No. 4, 1982
T,'K
T, 'K 303
293
283
273 B
h
t lo3k
D
C 1
1021
l o 3.2
3.3
3.L
3.5
3.6
:
-
3.2
3.3
7
3.L
1 I T 1 03, ~ - 1
I/T~IO~,*K-~
0
+
Figure 4. Plot of (PAH),,)/((PAHxWt)/(TSP)~ against 1 / T . Regression line: (1) Ph 4- An (0),(2) BaFlren BbFlren (O),(3) MePh 4- MeAn (O), (4) Ch BaAn 4- tri-Pheny (W), (5) Fi ( O ) , (6) BFlran (+), (7) Py (A),(8) BaP 4- BeP (A). For abbreviations of the PAHs, see Table 11.
+
plain the state of PAHs in the ambient air. As the total particulate surface is considered to be much higher than that covered by the PAHs in the ambient air (TSP/total PAHs = 280-760 w/w), the Langmuir adsorption equation in the low fractional coverage can be used for PAH,,, and PAH,,, on the particulate: 6, = b,P, (l) where 6, is the ratio of the particulate surface covered by PAH, to the total particulate surface, b, is the ratio of the rate of absorption to the rate of desorption, and P, is the vapor pressure of PAH,. 6, is also expressed as
6, = Kox(PAHxpat)/ (TSP)
(2)
where KO,is a constant of proportionality, (PAHxpaJis the concentration of PAH, at (ng/m3), and (TSP) is the concentration of TSP (ng/m3). In a relatively narrow range of temperature, the following equation is approximately valid: Px = Kpx(PAHxvap) (3) where Kpxis a constant of proportionality and (PAH,,,) is the concentration of PAH,ay From eq 1-3 the following relation is obtained: l / b x = Kx(PAH,vap)/((PAHxpa,)/(TSP)) (4) where K, = K ,/KO,.Since b, is a unique function of (PAHXpat)/(TSP)J can be retemperature h27.1,bh 28.2,b3j 25.6g.j 28.3,i9k 28.5i*'
10. Heat of sublimation of Ph. Heat of sublimation of An. Heat of sublimation of BaAn. See ref 13. J Heat of sublimaof sublimation of BePy.
lated to ambient temperature ( T , K). If the atmospheric PAHs are sampled by using the apparatus (Figure 1 ) under ideal sampling conditions where concentrations of the PAHs and T are constant, (PAHxvap)/{ (PAHxpat)/(TSP)] could be explicitly related to T for the individual PAHs. Deviations from the relation may be caused or increased with degree in variation of the sampling conditions and in inaccuracy of the analysis. Because Osaka, Japan, has a marine climate, variation of atmospheric conditions on a given day is relatively minor throughout the year (e.g., variation of temperature on a typical day is f2.5-5.5 K). Sampling under a sudden change of weather conditions (such as on a stormy day) was avoided in the investigation. Most of the PAYS were determined in the range of good analytical accuracy except for a part of the data for the five-ring PAHs in the vapor phase. Thus, the data indicated in Table IV may be used to discuss the above relation with a few exceptions; i.e., the data of phenanthrene anthracene for which the collection efficiency was lower than 90% above 25 O C (298 K) could not be used, and the data of benzofluoranthene and BaP BeP in the vapor phase that were below the detection limits were of no use. log [(PAH,,,,)/ {(PAH, ,,)/(TSP)}] was plotted against 1 / T for the individual f'AHs. Figure 4 shows that nearly linear relations were obtained between the two quantities for the PAHs at the ambient temperature levels. As a result, the following equation is assumed to be valid:
194
heat of sublimation, kcal/mol
-0.881 -0.854 -0.897 -0.892 -0.892 -0.942 -0.896 -0.834
termined values exceeded 15%. The constant A seemed to be related to the heat of sublimation for the individual PAHs. Thus, the state of the three- to five-ring PAHs in the ambient air is considered to be well explained by using the Langmuir adsorption concept although the constants A and B might be different in a different climate, in a different type of city, and/or in a different sampling apparatus. In closing, it is suggested that improvement of various PAH data obtained by conventional methods may be possible by using the Langmuir adsorption concept.
Acknowledgments We cordially thank H. Miyata, University of Osaka Prefecture, for his assistance in interpretation of the data.
Literature Cited (1) Cautreels, W.; Cauwenberghe, K. V. Atmos. Environ. 1978, 12, 1133-41. (2) De Wiest, F.; Rondia, D. Atmos. Environ. 1976,10,487-9. (3) Yamasaki, H.; Kuwata, K.; Miyamoto, H. Bunseki Kuguku 1978,27,317-21. (4) Pupp, C.; Lao, R. C.; Murray, J. J.; Pottie, R. F. Atomos. Environ. 1974, 8, 915-25. (5) Lao, R. C.; Thomas, R. S.; Oja, H.; Dubois, L. Anal. Chem. 1973,45, 908-15. (6) Simon, C. G.; Bidleman, T. F. Anal. Chem. 1979,51,1110-3. (7) Peters, J.; Seifert, B. Atmos. Environ. 1980, 14, 117-9. (8) Commins, B. T. Nutl. Cancer Inst. Monogr. 1958, No. 9, 225-33. (9) Brunauer, S. "The Adsorption of Gases and Vapors"; Princeton University Press: Princeton, NJ, 1945; Vol. 1, Chapter 4. (10) Hoyer, H.; Peperle, W. 2. Elektrochem. 1958, 62, 61-6. (11) Inokuchi, H.; Shiba, S.; Handa, T. Bull. Chem. SOC.Jpn. 1952,25, 299-302. (12) Wakayama, N.; Inokuchi, H. Bull. Chem. SOC.Jpn. 1967, 40, 2267-71. (13) Murray, J. J.; Pottie, R. F.; Pupp, C. Can. J . Chem. 1974, 52,557-63.
Received for review April 7,1980. Revised manuscript received September 2, 1981. Accepted November 19, 1981.
