leaving the other conditions for gas generation unchanged. It seems that a higher air flow rate in this range facilitates the generation of gas by removing the vapor from the surface of solution. Reaction Mechanisms of SO2 Generation. Reaction mechanisms of SO2 generation are shown in Equations 2,3, and 4: NaHS03 HS03H2S03
-
Na+
+ H+ +
+ HSO3-
(2)
erator is excellent and the generation sustains for several hours a t least. The concentration varies to a smaller extent with changes in temperature and air flow rate than with the permeation tube technique. The prepared gas contains some water vapor which is preferred for experiments meant to simulate the real atmosphere. In this paper, SOz, NO, NOz, HCN, HzS, and NH3 gas generation was described, but other gases such as hydrogen fluoride and carbon dioxide can also be prepared by the same technique.
H2S03
(3)
Literature Cited
(4)
Saltzman, B. E., Anal. Chern., 33,1100 (1961). (2) O'Keeffe, A. E., Ortman, G. C., Anal. Chern., 38, 760 (1966). 13) O'Keeffe. A. E.. Ortman. G. C.. Anal. Chem.. 39.1047 (1967) (4) Scaringelli,F. P., O'Keefe, A. E., Bosenberg, E., Bell, J. P., Anal. Chem.. 43,871 (1970). (5) Lucero, D. P., Anal. Chern., 43,1744 (1971). (6) West, P. W., Gaeke, G. C., Anal. Chem., 28,1816 (1956). (7) Saltzman, B. E., Anal. Chem., 26,1949 (1954). (8) Jacobs, M. B., Braverman, M. M., Hochheiser, S., Anal. Chern., 29,1349 (1957). (9) Frant, M. S., Ross, J. W., Riseman, J. H., Anal. Chern., 44,2227 (1972). (10) Thomas, R. F., Booth, R. L., Enuiron. Sci. Technol., 7, 523 (1973).
+
H20 t SO2
NaHS03 dissociates into Na+ and HS03- in a solution (Equation 2). If the p H of the solution is lowered by the addition of H+, the reaction tends to move to the right sides in Equations 3 and 4. In other words, the enhanced production of SO2 due to the increased H+ can be explained on the basis of Equations 3 and 4. Conclusions
The new technique for preparation of gases of a known concentration presented here makes it possible to prepare gases for environmental measurements and studies. The apparatus and operations of this technique are simple. The stability of the concentration of gas generated from the gen-
(1)
Received for review November 17,1978. Accepted October 22,1979. The authors are grateful that this research was supported in part by the Takeda Foundation.
Correlation between the Concentrations of Polynuclear Aromatic Hydrocarbons and Those of Particulates in an Urban Atmosphere Takashi Handa", Yoshihiro Kato, Takaki Yamamura, and Tadahiro lshii Department of Chemistry, Faculty of Science, Science University of Tokyo, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162, Japan Kyo Suda Hitachi Ltd. Central Research Laboratory, 1-280, Higashi-Koigakubo, Kokubunji, Tokyo 185, Japan
T h e atmospheric levels of polynuclear aromatic hydrocarbons (PAHs) and the size distrihution and number concentration of particles were measured a t several sites in the Tokyo metropolitan area. The concentrations of benzo[ghi]perylene (B[ghi]P), benzo[a]pyrene (BaP), perylene, chrysene, benz[a]anthracene (Bail), and pyrene were determined with a high-volume air sampler, and the number concentrations of particles ranging in size from 0.1 to 0.2 pm were determined by a n optical counter. For capturing the missing fractions of four-membered PAHs (pyrene, BaA, etc.), an improved collection system with traps cooled by liquid nitrogen was developed. Linear relationships between the contents of B[ghi]P, BaP, and perylene and particles were established. It was found that the ratio of the atmospheric PAH level to the B[ghi]P level was in fairly good agreement with that based on the average PAH levels in automotive exhausts from 26 Japanese cars. It is well known that polynuclear aromatic hydrocarbons (PAHs) exist in the atmospheric environment. PAH compounds are emitted from many sources including internal combustion engines. Experiments with animals ( 1 , 2 ) indicate that benzo[a]pyrene (BaP) and related compounds are carcinogenic. In addition, it was established that automotive exhaust gases contain considerable amounts of very fine particles. There is no doubt that the automobile is the single most important source of atmospheric PAHs in big cities. 416
Environmental Science & Technology
Several investigators have shown that PAH content depends on the size of suspended particulate matter, especially when the size is below -3 pm (3,4 ) . This finding was further supported by the analysis of soils ( 5 ) .The relationship of traffic density to the atmospheric PAH concentration was also measured a t four Los Angeles sites (6). An improved optical counter with He-Ne laser as a light source (7, 8 ) , capable of detecting particles with diameters of 0.06-10.0 pm, was used to characterize the size distribution of the solids from different combustion sources (9, I O ) . This paper is primarily concerned with the correlation between the number concentration of suspended particles and PAH levels in an urban atmosphere as related to traffic. In addition, a n improved collection method for four-membered PAHs in the atmosphere is described. Experimental
Measurement of Particle Size Distribution. An improved optical counter was employed for the measurement of the size distribution and number concentration of particles suspended in air. The minimum detectable size of 0.06 p m in diameter was attained by minimizing the signal-to-noise ratio (S/N) for the scattered intensity of a single particle (8).T h e counter detects particle sizes in three ranges (0.06-0.1,O.l-1.0, and 1.0-10.0 p m in diameter) by varying the diameter of the incident beam in three steps (25 pm, 100 pm, and 1mm). Since the adjustment of the equipment for precision measurements is rather time consuming, the method was used only in a se0013-936X/80/0914-0416$01.00/0
@ 1980 American Chemical Society
lected number of the particle size distributions of urban aerosols. Instead, a more easily operated counter (Hitachi TSI-500 type), which covers the size ranges of 0.1-1.0 and 1.0-10.0pm, was regularly employed in the field measurements. This apparatus is capable of determining the number concentration of particles with a coincidence loss of 1%,except a t high concentrations. T h e pulse signals could distinguish particles of nine different size ranges: 0.1-0.2,0.2-0.3,0.3-0.4, 0.4-0.5,0.5-1.0, 1.0-2.0, 2.0-4.0, 4.0-6.0, and 6.0-10.0 pm, in diameter. The counting time depended on the actual number concentration. The division into these ranges was conditioned by the theoretical scattering cross-sections, taking for the refractive index a value of m = 1.592 and k = 0, which corresponds to polystyrene lattices. This value differs from the average optical indexes of urban aerosols (rn = 1.50,k = -0.5). However, calculations have shown that this difference in the refractive index had no effect on the determination of particle size distribution. In the specific case of the Tsuburano tunnel, the values of m = 1.80 and k = -0.5 were used. In this case, the aerosol consisted primarily of soot generated by diesel trucks, which accounted for -60% of the traffic during the measurements. The coincidence loss, which is inevitable when counting particles a t high concentrations, was corrected as reported in an earlier paper (9). In addition, some particle distributions were obtained by mobility estimations in an electric field (11, 12). S a m p l e Collection. Aerosol sample collections and measurements of the size distributions and number concentrations of particles were carried out in the Tsuburano Tunnel on Tomei Expressway, in the Chiyoda Tunnel on Metropolitan Expressway, and a t the following six metropolitan sites: in urban areas a t Iidabashi, Kyobashi, and Shinjuku, in residential areas a t Mitaka and Kokubunji, and in an underground cab pool located along a shopping center in Shinjuku. Similar measurements were also carried out close to the exhaust tailpipes of two automobiles with spark retard: car A (1970 model year, displacement 1300 cm3, mileage 85 000 km) and car B (1975 model year, 1600 cm3, 24 000 km). Continuous measurements over an entire day (0:OO a.m.-12:00 p.m.) were carried out at Iidabashi to correlate the number concentration of suspended particles and the corresponding PAH levels to the traffic density. The atmospheric environment samples were collected on 8 X 10 in. glass fiber filters (Gelman Type A) using a highvolume air sampler (Staplex Co., Ltd.) for a period of 4 h. Because of high concentrations of suspended particles, the sampling period in Tsuburano and Chiyoda tunnels was only 1h. The automotive exhaust samples were collected on glass fiber filters by drawing the gas into the cooling apparatus. The collection was carried out on a chassis dynamometer a t a steady speed of 40 km/h after sufficient engine warm-up (13, 14). An Anderson low-volume cascade impactor (Kouritsu Instrument Co., Ltd.) consisting of eight fractionating stages and a back-up glass fiber filter was used in the Tsuburano Tunnel. The eight anticorrosive disklike aluminum stages had glass capturing plates on the bottom and a glass fiber filter of 8 cm in diameter a t the lowest end of the cascade system. At a flow rate of 1 cfm (28.3 L/min), the sampler fractionates suspended particulate matter into eight aerodynamic size ranges according to the calculated 50% cutoff diameters given as follows: stage no.
diameter, pm
stage no.
diameter, pm
1 211.0 6 1.1-2.1 2 7.0-11.0 7 0.65-1.1 3 4.7-7.0 8 0.43-0.65 4 3.3-4.7 back-up 10.43 5 2.1-3.3 filter All measurements mentioned above were performed in August 1977.
C C S -a
A
glass fiber thermometer filter
n
filter
vacuum Pump
methanol nitkogen
k
' i i-.rsi.'
L
---+I
Part . -. .
Part ,
glass fiber filter
Second
thermometer
I
high volume a i r sampler
f r o m liquid nitrogen liquid nitrogen
C C S -b Figure 1. Schematics of cooling collection systems: (CCS-a)low flow rate (3.2 cm/s), a vacuum pump is employed for the suction of air; (CCS-8)high flow rate (14.4 crn/s), a high-volume air sampler is employed for the suction of air
In order to collect four-membered PAHs as quantitatively as possible, two cooling collection systems (CCS-a and CCS-b) were developed which were used a t Iidabashi in December 1977. As illustrated in Figure 1,both collection systems consist of a glass fiber filter, a liquid nitrogen cooling system with a condenser and traps in series, and a back-up glass fiber filter connected with a suction pump. A vacuum pump was employed for CCS-a with an average air flow rate of -1.3 m3/h; the average rate of air passing through the first filter was -3.2 cm/s, and the average temperature in the cooling traps was --25 "C. The traps had to be changed several times in the course of an experiment to remove accumulated ice flakes from the condensed moisture in the air. To obtain a sufficient amount of PAH for fluorometric analysis, the sampling was performed for about 63 h in the daytime (9:OO a.m.-6:00 p.m.) during 1 week. The high-volume air sampler (CCS-b) was employed for a shorter collection time (not less than 4 h) a t 23.4 m3/h (14.4 cm/s) and a t -7 "C. E x t r a c t i o n a n d Analysis. All solvents employed were of spectrograde purity. Materials soluble in methanol and benzene were recovered from the filters by means of an ultrasonic method (15).The procedure for the recovery of PAH in the tar collected from the automotive exhaust gas was described in detail previously (13). T o provide sufficient amounts of PAH for the fluorometric analysis, dust collected in nine stages of the Anderson cascade impactor was combined into three fractions: d 5 0.43 pm, 0.43-2.1 pm, and 2 2 . 1 pm. Subsequently, the organic matter was extracted in a Soxhlet with benzene for 9 h. The matter collected in CCS was recovered by solvent extraction in two parts: from the glass fiber filter (Figure 1) and from the rest of the apparatus, including the second filter. Each solution containing PAH was condensed to 3-10 mL at a temperature of
