(15) Strickland, J. D. H.; Parsons, T. R. “A Practical Handbook of Seawater Analysis”; Fisheries Research Board of Canada: Ottawa, 1968. (16) Lean, D. R. S.; Burnison, B. K. Limnol. Oceanog. 1979, 24 917-28. (17) Duinker, J. C.; Kramer C. J. M. Mar. Chem. 1977,5,207-28. (18) Crecelius, A. Ph.D. Thesis, University of Washington, Seattle, WA, 1974. (19) Zaitsev, Y. P. “Marine Neustonology”; National Marine Fisheries Service, NOAA and NSF: Washington, DC, 1971. (20) Grant, G . C. Virginia Institute of Marine Sciences, Special Report in Applied Marine Science and Ocean Engineering, No. 192, .. 1979. (21) Duce, R. A.; Quinn, J. G.; Olney, C . E.; Piotrowicz, S. R.; Ray, B. J.; Wade,T. L. Science 1972,176, 161-3. (22) Piotrowicz, S. R.; Ray, B. J.; Hoffman, G . L.; Duce, R. A. J . Geophys. Res. 1972,77,5243-54.
(,3 ), Huntzicker. J . J.: Friedlander. S.K.: Davidson. C. I. Enuiron. Sci. Technol. 1975,9,448. (~, 4 ) National Research Council. “The TroDospheric Transport of
Pollutants and Other Substances to the Oceans”; Nationai Academy of Sciences: Washington, DC, 1978. (5) Food and Agricultural Organization of the United Nations, Fisheries Report No. 99, Suppl. 1,1971. (6) D.uce, R. A.; Hoffman, G . L.; Ray, B. J.; Fletcher, I. S.; Wallace, G. T.; Faschin J L.; Piotrowicz, S. R.; Walsh, P. R.; Hoffman, E. J. L. “Marine Pollutant Transfer”; WinJ.; Miller, J. ., Heffter, . L.; Duce, R. A., Eds.; Lexington Books, Lexington, MA, dom, 1976, pp 77-119. ( 7 ) Gatz, D. F. Water, Air, Soil Pollut. 1975,5, 239-51. ( 8 ) Cambray, R. S.;Jeffries, D. F.; Topping, G . Mar. Sci. Commun. 1979,5, 175-94. (9) Patterson, C. C.; Settle, D. J . Rech. Atmos. 1974,8,957-60. (IO) Crecelius, E. A. Mar. Chem. 1980,8,245-50. ( 1 1 ) Ijodge, V.; Johnson, S. R.; Goldberg, E. D. Geochem. J . 1978, 12,7-20. (12) Ludwick, ?J. D.; Fox, T. D.; Garcia, S. R. Atmos. Enuiron. 1977, 11, 1083-7. (13) Standard Reference Material 1648, U S . National Bureau of Standards, Washington, D.C. (14) Nielson, K. K. A d . Chem. 1977,48,645-8.
e.
J:
v.
Received for review September 29,1980,Reuised manuscript received April 24,1981. Accepted June 6,1981. This work was supported in large part by the U.S. Department of Energy, Contract No. DEAC06- 76RLO- 1830.
CORRESPONDENCE
predict, since on one hand sampling times are usually much longer, but on the other hand there is gas-aerosol equilibrium in the ambient atmosphere. While the first consideration would tend to increase the blow-off artefact, the second would tend to diminish it. Nevertheless, our hypothesis of selective volatilization of n-alkanes was consistent with the experimental data, since the alternation was more important for longer sampling times (e.g., in background areas) and higher temperatures. Recently, we performed some integrated measurements on organics in suburban areas. These consisted of (a) determination of concentrations of organics in the aerosol phase; (b) determination of concentrations of organics in the gas phase behind a Hi-Vol sampler, Le., the sum of the proper gas phase and blow-off contribution; (c) determination of concentrations of organics in the gas phase without blow-off contribution. Experimental details and results have been described (6). From these data it followed that, under normal sampling conditions, blow-off is only significant for a limited range of vapor pressures, Le., from C20 up to C24. Hence, we must conclude that the odd carbon number predominance, which is most pronounced from C27 up to C31, cannot be accounted for by a selective blow-off phenomenon, since there is essen-
SIR: In our most recent paper ( I ) , we have discussed in full detail the problem of the odd carbon number predominance of the n-alkanes in aerosol samples and have come to the conclusion that natural sources such as plant waxes indeed will account to a large extent for the presence of these compounds. Thus, we fully agree with the remarks of Simoneit (Enuiron. Sci. Technol. 1981, 15, 120). However, before coming to this conclusion, we believed it was imperative to rule out any possible high-volume filtration artefact that would result in a similar distribution profile for the n-alkanes. In the literature, ample evidence can be found for blow-off of the more volatile components from aerosol particles (2-4). Furthermore, in a laboratory experiment we have obtained evidence for the creation of an odd carbon number predominance of the n-alkanes as a blow-off artefact, starting from a continuous distribution profile (5).Thus, when an ambient aerosol sample was subjected to a flow of clean nitrogen gas ( 1 5 m 3 h-l for 10 h), significant losses of compounds were observed after analysis, compared to a nonexposed parallel sample. Not only was blow-off of n-alkanes measured up to C24, but also an increased odd carbon number predominance was detected in the aerosol phase. The magnitude of this effect in real Hi-Vol sampling was difficult to
Table 1. Carbon Preference Index of n-Alkanes vs. Particle Size (C24-C32) Cun
sample
(all
7.2
stager)
1.60 1.31 1.61 1.90
1.42 1.16 1.41 1.95
1.45 1.09 1.29 2.28
2.04 1.07 1.44 3.36
4.30 1.28 1.64 4.12
7.41 1.37 1.43 2.43
1.88 1.22 1.48 2.54
2.26 2.44
1.94 2.05
2.30 2.44
3.53 4.55
5.74 8.51
4.74 5.25
2.59 3.40
2.93 2.74
3.49 2.67
3.66 2.68
6.28 3.56
9.91 5.25
9.00 8.02
4.43 3.43
suburban Wilrijk SIautumn Wilrijk S2winter Wilrijk S3 spring Wilrijk S5 summer
rural Botrange B1 spr/sum Bottange B2 summer seashore Petten P I summer Petten P2 summer
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1981 American Chemical Society
Volume 15, Number 9, September 1981 1105
tially no detectable gas phase any more for the latter compounds. Therefore, it seems reasonable to explain the observed alternation of the higher n-alkanes by the natural contributions of vegetation to the ambient aerosol. Besides the odd carbon number predominance of n-alkanes which is most pronounced in our background samples, we have also identified on several occasions (7) diterpenoid compounds such as abietic, pimaric, and dehydroabietic acids which are typical of resinous plants. This is again in agreement with Simoneit’s remarks. No stable carbon isotope analysis has been performed on our samples, but it is important to stress that both the seasonal dependency of the carbon preference index (8)and its variation with particle size (using fractionated samples) sustain the natural origin of the higher n-alkanes. If dispersion of plant debris is the major source of generation of these aerosols, the carbon preference index for a size-fractionated sample should peak at the larger particle sizes, which is in contrast to the normal size distribution expected for condensation aerosols. This is precisely the case for most of our samples, as can be seen from Table I. Finally, we agree the word “pollutants” may not be appropriate for hydrocarbons and fatty acids derived from natural biogenic sources. However, even these naturally occurring compounds may have adverse health effects: thus, long-chain alkanes have been shown to behave as cocarcino-
gens in the experimental animal and to enhance the development of tumors, originally induced by polycyclic aromatic hydrocarbons. Therefore, the release of higher n-alkanes from natural sources into an atmosphere where several known carcinogens are present does constitute an additional health hazard and should be further evaluated.
Literature Cited (1) Broddin, G., Cautreels, W., Van Cauwenberghe, K., Atmos. Enuiron., in press. (2) Pupp, C., Lao, R. C., Murray, J. J., Pottie, R. F., Atmos. Enuiron., 8,915 (1974). (3) de Wiest, F., Della Fiorentina, M., Atmos. Enuiron., 10, 951 (1975). ( 4 ) de Wiest, F., Rondia, D., Atmos. Enuiron., 10,487 (1976). (5) Janssens, J., Van Vaeck, L., Van Cauwenberghe, K., unpublished results. (6) Van Vaeck, L., Van Cauwenberghe, K., Adu. Mass Spectrom., in press. (7) Broddin, G., Ph.D. Thesis, University of Antwerp, 1980. (8) Eichmann, R., Neuling, P., Ketseridis, G., Hahn, J., Jaenicke, R., Junge, C., Atrnos. Enuiron., 13,587 (1979).
L. Van Vaeck* G. Broddin K. Van Cauwenberghe Chemistry Department University of Antwerp (U.I.A.) 8-2610 Wilrijk, Belgium
Correction 1981, Volume 15
James L. Lake,* Roger F. Rogerson, and Curtis B. Norwood: A Polychlorinated Dibenzofuran and Related Compounds in an Estuarine Ecosystem. Page 551. The last sentence of footnote b to Table I should read as follows: Concentrations are not corrected for procedural losses.
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