Environ. Sci. Technol. 1985, 19, 707-7 16
and Meteorology for Roane County, Tennessee, During 1975”; Oak Ridge National Laboratory: Oak Ridge, TN,
(23) Tosteson, T. D.; Spengler, J. D. Environmetrics ’81, Society
1977.
1981. (24) Spengler, J. D.; Dockery, D. W.; Turner, W. A.; Wolfson, J. M.; Ferris, B. G., Jr. Atmos. Environ. 1981, 15, 23-30. (25) Letz, R. L.; Ryan, P. B.; Spengler, J. D. Environ. Monit. Assess. 1984, 4 (4), 351-359. (26) Duan, N. Environ. Int. 1982, 8, 305-309. (27) Tosteson, T. D.; Spengler, J. D.; Weker, R. A. Environ. Int. 1982,2, 265-268. (28) Gordon, G. E. Environ. Sei. Technol. 1980, 14, 792-800. (29) Colome, S. D.; Spengler, J. D.; McCarthy, S. Environ. Int. 1982,8, 197-212.
for Industrial and Applied Mathematics, Alexandria, VA,
(17) Turner, W. A.; Spengler, J. D.; Dockery, D. W.; Colome, S. D. J . Air. Pollut. Control. Assoc. 1979,‘29 (7), 747-749. (18) Treitman, R. D.; Spengler, J. D.; Tosteson,T. D. “Quality
(19)
(20)
(21) (22)
Assurance Project Plan”;Research Triangle Institute, U.S. Environmental Protection Agency Research Triangle Park, NC, 1981. Biddeson, D. L.; Eaton, W. C. “Performance and Systems Audit of the Respirable Particulate Exposure Study”;Research Triangle Institute, U.S. EnvironmentalProtection Agency: Research Triangle Park, NC, 1981. Eaton, W. C.; Arey, F. K.; McKee, J. L. “Systems Audit, 1982, Harvard School of Public Health Six-City Study”; Research Triangle Institute, U.S. Environmental Protection Agency: Research Triangle Park, NC, 1982. Quackenboss, J. J.; Karanek, M. S.; Spengler,J. D.; Letz, R. E. Environ. Int. 1982,8, 249-258. Ju, C.; Spengler, J. D. Environ. Sei. Technol. 1981, 15, 595-596.
Received for review June 14,1984. Revised manuscript received February 5,1985. Accepted March 5,1985. This work was funded by the US.Environmental Protection Agency under Cooperative Agreement CR808536010 and by general support provided to the Harvard Air Pollution Health Study under NIEHS Grant ES01108 and Electric Power Research Institute Grant RP-1001.
Characteristic Parameters of Particle Size Distributions of Primary Organic Constituents of Ambient Aerosols Luc Van Vaeck and Karel A. Van Cauwenberghe”
Department of Chemistry, University of Antwerp (U.I.A.), B-26 10 Wilrijk, Belgium Particle size distributions have been measured for nonvolatile organic constituents of ambient aerosols, sampled by Sierra and Andersen Hi-Vol cascade impactors, in suburban, rural, and seashore areas in Belgium and the Netherlands during the four seasons. The distributions of polycyclic and aza-heterocyclic aromatic hydrocarbons, n-aliphatic hydrocarbons, and carboxylic acids determined by gas chromatographic-mass spectrometric analysis are compared by using different formats. Results are discussed with respect to (1)generation and aerosol incorporation processes, which show condensation in the accumulation mode W2.5 pm) of anthropogenic combustion related compounds and natural contributions of the biosphere in the dispersion mode, and (2) aerosol aging processes, which show that the particle size distributions of its constituents tend to shift toward a larger size within the accumulation mode upon atmospheric transport. This is reflected in the mass median equivalent diameters of the partial cumulative distributions for the accumulation mode. Introduction The identification of toxic trace pollutants in ambient aerosols (e.g., heavy metals and polycyclic aromatic hydrocarbons) has led to the development of highly sensitive and specific analytical techniques for the quantitative determination of trace constituents in airborne particulate matter. Furthermore, the well-documented relationship between aerodynamic particle size and retention of aerosols in the respiratory tract resulted in the need for analyzing size fractionated samples, in order to better assess the health hazards involved with particle inhalation. Thus, the measurement of particle size distributions of individual pollutants became a major challenge to the environmental chemist. Detailed information can be found in the literature on the mechanisms of formation, aging, and removal of aerosol particles from the atmosphere. Number, surface, volume, 0013-936X/85/0919-0707$01.50/0
and mass size distributions of aerosols have been measured or calculated by using experimental data obtained with sophisticated fractionating equipment with high particle size resolution. An aerosol physical model has been proposed, which explains the presence of many organic compounds in aerosols by condensation and adsorption of combustion related gases of the second generation onto primary particles with high specific surface and thus predicts the enrichment of those organics in the accumulation mode (1-6). In this paper we discuss the particle size distributions of the organic constituents of ambient aerosols using different analytical formats and want to point out how well the generally accepted mechanisms of aerosol generation and aging described for the whole particle are reflected into the particle size distributions of its individual organic compounds. However, in view of the limited particle size resolution of the Hi-Vol cascade impactors commonly used for collecting large samples and their nonideal performance subject to systematic errors, the variations in particle size distributions of organics between different samples are expected to be more difficult to detect. For several years, the major goal of our research effort has been to build an extensive data base for the particle size distributions (psd) of a variety of organic trace constituents, both of anthropogenic and of natural origin. Ambient aerosols were collected in suburban, rural, and seashore areas. Chemical analysis of the different size fractions was performed for about 60 compounds, belonging to the series of n-alkanes and carboxylic acids as well as polycyclic and aza-heterocyclic aromatic hydrocarbons (PAH). In previous reports the sampling equipment and analysis methodology were described, and selected preliminary results were presented (7-12). This paper is restricted to a phenomenological discussion of the psd. A discussion of the toxocologically relevant parameters derived by applying a realistic model for particle
0 1985 American Chemical Society
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Table I. Equivalent Cutoff Diameters at 50% Collection Efficiency of the Impactors
stage no.
1 2 3 4 5 6 7 8 9
cutoff diameters, @ma Sierra Hi-Vol Andersen Hi-Vol at flow rate at flow rate of 68 m3 h-' of 34 m3 h-' >7.2 7.2-3.0 3.0-1.5 1.5-1.0 1.0-0.5 7.0 7.0-3.3 3.3-2.0 2.0-1.1 7 pm
1.4
1.2
1.3 1.7 1.4 1.6 1.3 1.6 1.6 4.2 3.9 4.9 3.1 5.4 3.7 2.3 1.8 1.6 3.6
1.6 2.4 1.5 1.9
1.8 3.8 2.0
1.6 1.5
1.6 1.5 1.7 1.2 1.4 1.8 2.7 2.5 2.6 2.7 3.6 2.8 1.6 1.9 1.6 2.3
1.8
1.6 2.0
1.4 1.6 2.0
2.5 2.3 2.9
2.3 2.2 2.2
3.5 4.1
3.5 2.9
1.7
2.1 1.7
2.6
0.5-1 pm
1.5 2.2
1.7 2.4
2.2
1:aI
1.6
1.7 1.7 6.6 4.9 9.2 5.0
7.4 4.5 4.7 2.1 1.6 5.1
2.1
1.8 1.5 2.5 5.0 2.9 5.9 9.0 12.3 8.9 7.9 3.0 2.0 2.6
CPI calculated from hexacosane to dotriacontane. bFor Andersen samples the submicron fraction is not further resolved.
WAW 3
ElCOSANOlC ACID
1
3
DAW 1
7
1
1
3
7
wsz 1
1
1
3
7
HENEICOSANOIC ACID
1
3
7
3
:
M
BSZ 1
2 1
1
3
7
1 3 7
1 3 7
1 3 7
1
3
7
1
1
7
1
3
7
1
3
7
1 3 7
1 3 7
1
3
7
PENTACOSANOIC ACID 3
7
3
HEXACOSANOIC ACID
AM ,
,
A log Dp
(ng
mm31 vs
log
oP (pm)
Figure 5. Slre distrlbutlons of higher carboxylic acids.
pointed to dispersion of plant material. However, the differences for the preference index are less pronounced. The evolution of psd of carboxylic acids upon aging is again featured by the depletion of the submicron fraction, but in this case, no clear enrichment of the contributions in the larger particle size ranges can be found. One could explain this by the overlap between the accumulation and 714
Envlron. Sci. Technol., Vol. 19, No. 8, 1985
the dispersion mode, as was the case for the higher aliphatic hydrocarbons. Parameters of the partial cumulative distributions are given in Table IX. From the MMED' and the B; values it follows that the distribution shift toward larger particle size is similar to the one found for the PAH: upon longi term aging, the MMED' values increase with 0.2 ~ nand
Table VIII. Comparison of MMED and ug of Aliphatics, Determined for Total Particle Size Range and for Accumulation Mode
n-heptacosane total
