Environ. Sci. Technol. 1988,22,1207-1215
Hunt, J. R.; Pandya, J. D. Environ. Sci. Technol. 1984,18, 119. Wang, T. R.; Koh, R. C. Y.; Brooks, N. H. In Proceedings 5th International Ocean Disposal Symposium; Corvallis, OR, 1984. Turner, D., METRO, Seattle,WA, personal communication, 1986. Galehouse,J. S. In Procedures in Sedimentary Geology; Carver, R. E., Ed.; Interscience: New York, 1971;pp 69-94. Tennant, D. A,; Walker, S.; Lavelle, J. W.; Baker, E. T., Technical Report ERL PMEL-69; NOAA: Boulder, CO; 1987. Krumbein, W. C.; Pettijohn, F. J. Manual of Sedimentary Petrology;Appelton-CenturyCrofts: New York, 1938. Koh, R. C. Y. In Ocean Disposal of Municipal Wastewater: Impacts on the Coastal Environment; Myers, E. P., Ed.; M.I.T. Sea Grant Program: Cambridge, MA, 1983; pp 129-176. Kranck, K. Can. J. Earth Sei. 1980,17, 1517. Bradley, R. A,; Krone, R. B. J. Sanit. Eng. Diu., Am. SOC. Civ. Eng. 1971, 97, 59. Treweek, G. P.; Morgan, J. J. Environ. Sci. Technol. 1977, 11, 707. Garber, W. F.; Ohara, G. T. J. Water Pollut. Control Fed. 1972,44, 1518. Hannah, S. A.; Cohen, J. M.; Robeck, G. C. J . Am. Water
of these particles in the laboratory qualitatively resemble the formation environment in the ocean, these results suggest that the fine particles in an ocean discharge have small enough settling velocities that they are likely to be transported out of the discharge area. This conclusion would hold unless biologically mediated settling processes (macroaggregates or fecal pellets, for example) play an immediate and significant role in sludge particle deposition, or unless coarse particles of the discharge entrain smaller particles by differential settling and cause some fraction of them to be locally deposited. Acknowledgments
We thank Kenneth Bloomstine for his diligence in the sizing laboratory. Appreciation is also extended to Ronald Gibbs who kindly provided fresh samples from the Middlesex and Owl’s Head treatment plants, to Steven McLean who arranged the sample acquisition at Hyperion, and to Deborah Turner of METRO, Seattle, for incubation experiments. Helpful discussions of the sludge settling problem with Thomas O’Connor are also acknowledged.
Literature Cited Ozturgut, E.; Lavelle, J. W. Mar. Geol. 1986, 69, 353. Jenkins, A,; Whalen, D.; Konwar, L.; Gibbs, R. J. Report to Ocean Assessment Division; NOAA: Rockville, MD, 1985. Hunt, J. R. Environ. Sci. Technol. 1982, 16, 303. Brooks, H. N. Settling Analyses of Sewage Effluents; Los Angeles, CA, 1956; memorandum to Hyperion engineers. Myers, E. P. Ph.D. Dissertation, California Institute of Technology, Pasadena, CA, 1974. Faisst, W. K. In Particulates in Water;Kavanaugh, M. C., Leckie, J. O., Eds.; Advances in Chemistry 189;American Chemical Society: Washington, DC, 1981; pp 259-282.
Works Assoc. 1967,59, 843.
Gibbs, R. J. J. Sediment. Petrol. 1982, 52(2),657. Morel, F. M. M.; Schiff, S. L. In Ocean Disposal of Municipal Wastewater: The Impact on Estuary and Coastal Waters; Myers, E. P., Ed.; M.I.T. Sea Grant Program: Cambridge, MA, 1983; pp 249-421. Received for review November 25, 1986. Revised manuscript received January 20, 1988. Accepted May 2, 1988. The work was supported by NOAAIEnuironmentalResearch Laboratories and by NOAAINational Ocean Service.
Aerosol Formation by the Photooxidation of Cyclohexene in the Presence of Nitrogen Oxides Katsuyukl Izuml, * Kentaro Murano, Motoyuki Mizuochi, and Tsutomu Fukuyama Division of Atmospheric Environment, The National Institute for Environmental Studies, P.O. Tsukuba-gakuen, Ibaraki 305, Japan
Photochemical aerosol formation from cyclohexene (C&10) was studied in a ppm concentration range in the presence of nitrogen oxides. It was found that the aerosol was formed by the reaction of with ozone (OJ, while the products of the C6H10 + OH reaction had substantially no contribution to the aerosol production. The average carbon-based aerosol yield from the O3reaction was shown to be 18.3 f 3.6% for a CGHlo initial concentration range of 5-10 ppm. However, the yield was found to decrease nonlinearly as the initial concentration was decreased, and consequently, it was pointed out that, in obtaining the yield in the actual environmental condition, an extrapolation of the result from higher concentration experiments to a lower concentration region should be done with caution. Information about humidity effects on aerosol formation was also obtained. In addition, the accuracy of the rate constant for the reaction of C6Hlo with O3was checked. H
Introduction
On an element basis, carbon is the most abundant constituent found in both urban and nonurban aerosols, and from the viewpoint of air pollution control, it is of 0013-936X/88/0922-1207$01.50/0
particular importance to investigate the modes of formation of organic aerosols in the air contaminated by anthropogenic hydrocarbons. Surveying the existing data on the composition of urban aerosols, it is recognized that a significant fraction of organic particulate matter is constituted of difunctional compounds such as dicarboxylic acids, dialdehydes, oxo carboxylic acids, etc., and their most likely precursors are considered to be cycloalkenes, which are found in gasoline and auto exhaust (1-5). In fact, aerosol formation from cycloalkenes was studied several times by means of smog chambers mainly with attention to photochemical reactions (6-9) [investigations before 1977 were reviewed by Grosjean (9)]. Grosjean and Friedlander (8) made chemical analyses of the aerosol products and found dicarboxylic acids and other a,o-difunctional oxygenates bearing carboxylic, formyl, hydroxyl, or nitrato groups. They further proposed formation mechanisms for those compounds that involved initial attack by ozone (0,) and hydroxyl radical (OH) on cycloalkenes. More recently, Hatakeyama et al. (IO)made extended quantitative analyses of the cyclohexene (C6H10) + O3reaction products and determined the fraction of C6H10 converted into aerosols.
0 1988 American Chemical Society
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Through those and other studies, fairly reliable knowledge was accumulated which indicated that the major chemical reactions undergone by cycloalkenes in the atmosphere were those with Os and OH. However, little was known about the relative importance of these species in the aerosol formation reactions, the only available information being a statement by Grosjean and Friedlander (8) that both species might yield essentially the same products. Moreover, most of the past studies were directed to the identification of the reaction products, and consequently, quantitative data on the aerosol yield from lowconcentration hydrocarbons were quite deficient, although they were most important in planning a pollution control strategy. The effect of such a parameter as relative humidity (RH) also remained to be investigated in more detail. Taking these circumstances into account, photoirradiation experiments have been carried out in this study with gas mixtures containing different concentrations of C6H10, nitrogen oxides (NO,), and water (H20)vapor. The primary purpose is to determine quantitatively the yields of the particulate products from the O3and the OH reactions and thus to get conclusive information as to which of these species is more important in forming aerosols. Also, the effect of humidity has been investigated to expand the knowledge on the aerosol formation mechanism. Prior to these experiments, an attempt was made to supply an accurate value of the rate constant for C6H10 + O3 reaction, since widely scattered values are found for this constant in the literature.
Experimental Section Four series of experiments were conducted to get different kinds of information: (1) For the reason mentioned in the Introduction, the rate constant for the C6H10 + O3reaction was determined to confirm which of the literature values was accurate. (2) Irradiation experiments were carried out by varying the C6H10 initial concentration and RH to examine the dependence of the aerosol formation on these parameters. (3) The reaction of C6H10 with OH was investigated in separate experiments, in which OH was generated by the photolysis of methyl nitrite (CH30NO)in the presence of NO (11,12),and the aerosol yield from the C6H10 + OH reaction was compared with the yield from the C6H10 + O3reaction. (4) The carbon content in the particulate products was quantified to determine the aerosol yield on the basis of this element; the analysis for nitrogen content was also made. All the experiments were carried out in a cylindrical and evacuable 4-m3 aerosol chamber. Since an outline of the chamber facilities was given previously (13,14),only the experimental procedures relevant to this study are described in the following. The matrix air for the reaction was taken from the outdoors, and the impurities were removed to a level of 2 ppb for NO,, 0.04 ppm C for total hydrocarbons, and 2 cm9 for condensation nuclei. After being passed through a humidity regulator, the air was introduced into the chamber to a prescribed pressure, and then the reactants were added to the air with a stream of ultra-high-purity nitrogen from gas-handling equipment. After the gases were mixed with electric fans, the RH of the mixture was determined by measuring the dew point (Yokogawa Electric Works, Model 2586 dew point meter). Concentrations of C6Hlo were determined by a gas chromatograph with a flame ionization detector (FID-GC), which was operated at 368 K with a 2 m X 3 mm 0.d. stainless steel column with 20% Silicone OV-101 on 60-80 1208
Environ. Sci. Technol., Vol. 22, No. 10, 1988
Table I. Summary of Irradiation Experiments CBH1O
initial concn, ppm NO NOz
RH, %
no. of runs
0.3 0.3-4.9
0.03 0.01-0.40
0.03 10-50 0.015-0.60 30
8
4.8-10.2 5.1
0.44-0.87 0.5
0.61-1.44 0.58
5 1
4.6-53 48
7
purpose RH dependence [CBHIOIO dependence AOC detn AON detn
mesh AW-DMCS Chromosorb W. In order to check the interference in the GC analysis due to reaction products, analyses of the photoirradiated reaction mixtures were performed by changing the analytical conditions, namely, with longer column length, lower column temperature, and slower flow rate of carrier gas to enhance separation between peaks. However, in all the gas chromatograms, the peak for stayed single. It was thus found that the analysis for C6H10 was free from the interference due to products from both the O3and OH reactions. Concentrations of O3 and NO, were monitored by chemiluminescent analyzers (Monitor Labs, Models 8410 and 8440). Total number concentration of the aerosols was measured by a condensation nucleus counter, CNC (TSI, Model 3020), and monitoring of the size distribution was carried out by an electrical aerosol size analyzer, EAA (TSI, Model 3030). Output from the EAA corresponding to a particle diameter of less than 0.01 pm was neglected since the response of the instrument was known to be unreliable below this size (15). The raw data from the EAA were processed on the basis of the program of Sem et al. (16), which derives the real size distribution by allowing for the cross sensitivity. Determination of the Rate Constant for the Reaction of Cyclohexene with Ozone. The rate constant was determined by employing the pseudo-first-ordertechnique, namely, by measuring the O3decay rate in the presence of excess C6H10. A known amount of C6HIo was injected into the chamber, and after mixing, the initial concentration was determined. It was set in a range from 0.8 to 3.8 ppm. Then with the fans in operation, O3was added until its concentration was 0.08-0.105 times that of C6H10. The reactions were allowed to proceed in the dark in a dry condition ([H20]< 1ppm) at 303 f 1 K under a pressure of 1 atm, and the decay of the O3 concentration was monitored. Irradiation Experiments. In the experiments for observing the photochemical formation of the aerosol, the chamber was filled with the matrix air of a pressure of 820 Torr, and the reactants, C6H10, NO, and NO2,were added. In most of the experiments, the initial concentration of C6H10 ([C6Hlo]o)was set in a range from 0.3 to 4.9 ppm and those of NO and NOz were set approximately equal to of [C6H10]0. The initial conditions are summarized in Table I. Immediately after the RH was measured, the irradiation was started and continued for 70-80 min. It was provided by a solar simulator composed of 12 1.6-kW Xe lamps. Pyrex filters of 3 mm in thickness were used to remove spectral components shorter than 290 nm from the light to obtain an actinic distribution similar to that in the real sunlight. For all the runs, the intensity of the light as measured by the N02-photolysis rate constant was kept at 0.27 mi&, which nearly corresponded to the average actinic irradiance of the sun in summer. The initial temperature of the reaction mixture was adjusted to be 302 f 0.5 K; a rise in the temperature due to the irradiation was less than 2 K. It had been suggested in our previous study that, if there was any difference in humidity between the sheath air for
-
Figure 1. Effect of sheath air humldity on total number ( N ) ,surface area (S), and volume ( V ) concentrations of the aerosol measured by the EAA. RH denotes the relative humidity of the sheath air. The first two measurements were done by matching RH with the relative humidity of the chamber air, while in the latter two sheath air was much drier than the chamber air.
the EAA and the sampled chamber air, artificial growth or evaporation of the aerosol particles took place inside the EAA and it could cause a serious error in the size distribution measurement (14). Therefore, a test experiment was conducted to examine the effect of the sheath air humidity on the size distribution obtained by the EAA. In this experiment, a mixture of NO, NO2, and C&lo was irradiated in the chamber under a condition of RH = 50%. Then the light source was turned off, and four EAA measurements were made using the sheath air of different RH. In the initial two measurements, the RH of the sheath air was adjusted to be equal to that of the chamber air, while it was set less than 1% in the following two. Results for the total aerosol concentrations based on number ( N , surface area (S),and volume (V) are shown in Figure 1. It was found that N was independent of the sheath air humidity, whereas S and V were significantly decreased when the sheath air was drier than the chamber air. This observation indicates that the size distribution based on surface area or volume is modified unless the humidity of the sheath air and that of the chamber air are matched with each other. In order to avoid such artificial modification of the size distribution, the dew point of the sheath air was carefully kept within f0.5 K (f3% in RH at 302 K) of that of the air in the chamber. Another test experiment was carried out for the purpose of examining the stability of the aerosol in the chamber against deposition or evaporation. In this experiment, the aerosol was generated by photoirradiating a mixture of CGHlo and NO2,the light was turned off, and the particles were sampled twice in an interval of 60 min. Then the carbon content in the samples was determined according to a method described later to estimate the decay rate of the particulate carbon mass concentration. The estimate came out to be less than 2.8% h-l, being consistent with our previous data for sulfuric acid (H2S04)aerosol of comparable particle sizes (14). Since the decay was sufficiently small in view of the error in the carbon mass measurement (Table 111))we concluded that no correction for the decay was necessary. It was also confirmed that no significant wall decay was observed for the gas concentrations. Reaction of Cyclohexene with Hydroxyl Radicals. In the experiments to examine the C&10 OH reaction, 1.1ppm of CHBONO and 2.7 ppm of NO were added to the air containing 1.0 ppm of C6H10, and the mixture was exposed to the radiation. The relative humidity was adjusted to 50%. The OH radical is produced by a sequence of reactions starting from the photolysis of CH30N0 and reacts with CsHlo:
+
+
CH30N0 CH30 NO CH30 + O2 CHzO + H 0 2 HO2 + NO ---+ OH + NO2 C&lo + OH products Since NO suppresses the O3 formation, C6H10 is allowed to react only with OH. The decrease in the C6H10 concentration and increase in the aerosol volume concentration were monitored, and the aerosol yield from unit concentration of C6Hlo was calculated. Determination of Aerosol Organic Carbon (AOC) and Nitrogen (AON) Contents. Analyses for AOC and AON were carried out on the aerosol samples collected on tissue quartz filters (Pallflex 2500 QAST, 17 mm o.d.1, which were preheated to 873 K for 6 h to remove impurities. The AOC was quantified by a thermal carbon analyzer (TCA, Kimoto Denshi Co.) according to a method discussed by Wolff and Klimisch (17): In the TCA the sample was heated to 773 K under a flow of 0,; at this temperature all the organics were evaporated and subsequently oxidized to COPover a catalyst. Then the COz concentration was determined by an NDIR detector installed in the instrument. The AOC quantification procedure was calibrated by using quartz filters on which known amounts of adipic acid were deposited. For the determination of AON, the C02 detector in the TCA was replaced by a chemiluminescent NO, analyzer; the sample was put into combustion at 1073 K with continuously supplied 02,and the concentration of NO, stemming from the nitrogenous compounds in the sample was determined. The calibration was done with the filters impregnated with known amounts of NaN03 or NH4N0p The detection limit was as low as 0.1 pug of N. When an aerosol is collected on a filter for the purpose of chemical analysis, it should be examined as to whether or not gases are also caught on the filter media because of adsorption. The possibility of such adsorption has been pointed out for organic gases (8, 18) and for inorganic nitrates (19), but the aerosol sampling has been done so far without serious attention paid to the gas adsorption. In order to determine the amounts of adsorbed gases, the reaction mixture was sucked through a stack of three or four filters (a prefilter plus two or three backup filters) and total carbon and nitrogen caught by the backup filters were quantified. The results are summarized in Table I1 together with the initial concentration of the reactants. The data from the dark reaction of C6H10 with O3 are also included. Organic carbon and nitrogen contained in unused filters were as low as 1pg of C and 0.3 pg of N. The data in Table I1 indicate that adsorbed amounts of gaseous organic and nitrogenous compounds were about 10 pg of C and 0.3 pg of N, respectively, on an element basis. It was also found that the amount of organics adsorbed was almost independent of the initial concentrations of the reactants, the relative humidity, and the sampling volume. Two trials, elevation of the preheating temperature (runs P-6 and P-7) and exposure of the filters to nitric acid vapor (run P 4 , were made to see if the gas adsorption was reduced by these treatments, but little improvement was found. On the basis of these results, the experiments for the determination of AOC were done with higher initial concentration of (Table I); the aerosol samples were collected on the stack of filters; and AOC was determined by subtracting the average amount of carbon found on the backup filters from the amount collected on the prefilter to eliminate the contribution from the adsorbed gases. The rise in the initial concentration helped preserve the precision of the data, since the ratio of the aerosol production
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Table 11. Adsorption of Gases from Reaction Mixtures on Tissue Quartz Filtersa total C (pg) or N (pg) found on run no.
reactn conde
P-1 P-2 P-3 P-4 P-5 P-6 P-7 P-8 P-9' P-10 P-11 P-12 P-13d
A A A A A A A A A B
c c C
[C,Hl0] 5.0 5.0 5.0 10.0 10.0 10.0 10.0 10.0 5.0 1.0 0.5 1.0 1.0
init concn, ppm [NO] [NO,] [CH30NO] 0.5 0.5 0.5 1.0 1.0 1.0 1.0 1.0 0.5 2.2
[Os] RH,
0.5 0.5 0.5 1.0 1.0 1.0 1.0 1.0 0.5 0.6 2.0 2.0 2.0
%
30 30 4.6 30 30 30 30 30 48 30 30 30 30
unreacted CcHlo, ppm
filter treatmend
backup prefilter
1st
2nd
sampling vol, L
3.0 0.2 0.8 6.1 1.0 0 0 0 0 0.35 0 0 0
D D D D D E F G D D D D D
24.7 77.1 68.8 92.0 102 b b 78.2 2.7c 11.2 20.2 38.5 52.9
10.2 9.4 9.7
9.0 8.8 9.8 11.5 9.1 12.9 b 9.9 0 2 9.0 5.8 6.8 10.2
52.6 39.5 43.7 44.1 34.1 335 273 32.0 117 337 261 183 268
11.1 11.2
13.7 30.5 12.5 0.3c 9.0 5.9 8.2 9.9
OThe reaction mixtures were sampled in the dark through a stack of filters (a prefilter plus two or three backup filters; Pallflex 2500 QAST, 17 mm 0.d.). *Analysis was not done. cFor this run, nitrogen content was determined. dFor this run, total carbon on the third backup filter was also determined, resulting in 11.6 pg of C. eReaction condition: (A) reaction of the mixture under irradiation; (B)reaction of C6HI0with OH generated by CH30N0 photolysis; (C) reaction of CsHlowith O3in the dark. fFilter treatment: (D)preheating to 873 K for 6 h; (E) preheating to 1073 K for 6 h; (F) preheating to 1273 K for 6 h; (G) preheating to 1073 K and exposure to HN03 vapor.
to the gas adsorption became larger as the initial concentration was higher. The same procedure was applied for the determination of AON, although the adsorption of nitrogenous gases was, as mentioned above, found to be much smaller. It was found that the AOC concentration determined in the way described above was in good proportionality with the volume concentration V obtained by the EAA, provided that V was measured with dry sheath air (RH < 1%). As described later in detail, the volume concentration measured in this condition corresponds to the net volume of the organic condensate and is designated v d hereafter. The proportionality between [AOC] and v d was proved to be useful for correlating the data obtained by filter sampling and by EAA. Materials. The purest grades NO and NOz were obtained from Matheson Gas Products; NO was used after removing NOz by repeating freeze-thaw cycles in a bulb containing Ascarite kept at 77 K, while NOz was purified by distillation under reduced pressures. Cyclohexene was also of the purest grade available from Tokyo Kasei Kogyo Co. and was used after distillation under vacuum. Methyl nitrite, which was used as an OH radical source, was prepared from sodium nitrite (NaNOZ)and methanol in the presence of HzS04(13). It was then distilled at 195 K, and the distillate was stored in the dark at 77 K. Ozone was produced from ultrahigh-purity O2(Nihon Sans0 CO.; purity >99.998%) with a silent-discharge ozonizer (Nihon Ozone Co., Model 100) and purified by condensing it on silica gel cooled to 77 K to remove particulate matter generated in the discharge. The excess O2was pumped off and the remaining O3was used after being vaporized.
Results and Discussion Rate Constant for the Reaction of Cyclohexene with Ozone. Since the C6H10 concentration was in excess of the O3 concentration ([C6Hlo]o/[03]o 5 lo), and since the wall decay of the gases was negligible, the O3decay rate should conform to the pseudo-first-order expression
where kl is the second-order rate constant for the reaction of C&10 and 03.Figure 2 is a semilog plot of the O3 1210
Environ. Sci. Technol., Vol. 22, No. 10, 1988
Time
(min)
Figure 2. Time variation of 0,concentration in the dark reaction with excess CsH,o;a semilog plot to determine the apparent O3decay rate constant. The initial concentration of CeHI0 ([CeH,o]o)was 2.91 ppm.
2
06
L
0
1
[CaHlol
2
3 4 (ppm)
Figure 3. Dependence of the apparent O3decay rate constant (kew) on the average concentration of C8Hlo. From the slope of the line is obtained the rate constant for the CeH,, O3 reaction.
+
concentration, which decayed exponentially in accordance with eq 1. In this example, the initial concentrations of C6Hl0and O3were 2.91 and 0.24 ppm, respectively. It was found that the same amounts of C&10 and O3were consumed in the reaction. This satisfies the prerequisite of the pseudo-first-order technique that the stoichiometry of the reaction should be unity. From the slope of the semilog plot, the apparent O3 decay rate constant, k,, ,was evaluated to be 0.408 f 0.002 min-', with the error kmits corresponding to twice the standard deviation obtained in the least-squares fitting. Then the dependence of k,, on the C&lo concentration was examined to determine tke rate constant kl. In Figure 3, k,, is plotted against the average C6Hlo concentration, which is an arithmetic mean of the concentrations measured at t = 0 and 5 min. As shown in the figure, the plot yielded a linear relation passing through the origin. Least-squares fitting was again carried out to determine the slope of the line, and as a result, k, was determined cm3 molecule-l s-l (0.144 f to be (0.993 f 0.021) X
c
ij V
0
20
40 Time
60
80
(rnin)
Figure 4. Time variation of the gas concentrations in an irradlation experiment. The initial concentrations were 0.29, 0.025, and 0.025 pprn for C,H,,, NO, and NOz, respectively; relative humidity was 50 % .
0.003 ppm-' min-') at 303 f 1K with twice the standard deviation. This rate constant is in good agreement with cm3 molecule-l s-l at 297 the value (1.04 f 0.14) X f 1K, which was recently reported by Atkinson et al. (201, and also with that of 0.15 ppm-l min-l reported by Grosjean and Friedlander (8), but is significantly larger than cm3molecule-l that of Cadle and Schadt (21) (0.59 X s-l) and smaller than the values of Japar et al. (22) and Adeniji et al. (23) [(1.69 f 0.15) X and 2.04 X 10-la cm3 molecule-l s-l, respectively]. The reason for these discrepancies is not clear at present. The value obtained here was used in the later analysis for the estimation of the OH radical concentration. It was found that the use of Japar's or Adeniji's value led to negative OH concentrations. This result suggests the existence of error in these values. Aerosol Formation by Photoirradiation. An example of the time variation of the gas concentrations is shown in Figure 4. In this case, the initial concentrations of C6H10, NO, and NOz were 0.29, 0.025, and 0.025 ppm, respectively, and RH was 50%. NO disappeared at 20 min, while the concentration of NO, remained almost constant throughout the irradiation. The concentration of CBHlo gradually decreased to 0.06 ppm in 80 min. On the other hand, O3 began to be formed simultaneously with the start of the irradiation, showed a rapid increase until 40 min, and then leveled off at 0.14 ppm. A few runs were also conducted with higher initial NOJHC ratios (0.5-0.8) in order to examine the effect of the NO, concentration. In those runs, however, the reaction was found to proceed in a way considerably different from that in the lower NO,/HC case: the evolution of the aerosol was delayed and the size of the particles already exceeded the upper limit (1pm) of the EAA range at the onset of the formation. This paper deals with the lower NO,/HC case, in which the photoirradiation experiments were carried out with NO,/HC 0.2. Figure 5 shows the aerosol evolution process in the same run, as monitored by the EAA. In this figure, N , S, and y are plotted together with the geometric mean diameter, dp, of the particles. After the first formation of the aerosol waa detected at 12 min, N increased steeply to a peak value of 3 X lo5 crn9 at 16 min and then began to decrease because of the coagulation of the particles. In contrast, S and V continued to increase slowly until the later stages of the reaction, and the former approached a constant level of 3 X lo3pm2 cmS. These time variation patterns of N , S, and V have been well established in the gas-to-particle conversion processes (6,14,15,24). The size of the particles grew in parallel with the increase in S and rose
-
Time
(min)
Figure 5. Time variation of N, S,and Vconcentrations of the aerosol formed in the same experiment as in Figure 4. dp is the geometric mean diameter on the basis of N .
Figure 8. Total volume concentration (V) of the aerosol vs the amount of C,Hlo reacted with 03.
monotonically to an almost steady value of 0.08 pm. In all runs of the experiment, the geometric standard deviation (a,) of the number-basis size distribution was found to be constant at 1.4 f 0.1 throughout the irradiation. This up value is comparable with that for the H2S04 aerosol generated by photooxidation of SOz (14) and indicates that the width of the distribution was relatively narrow. Figure 6 shows a plot of V against the amount of C6H10 lost by the reaction with 03,the latter quantity being calculated as a time integral k&[C&0][03] dt. As shown here, there appears a closely linear relation between these quantities. This supplies strong evidence that the aerosol from C&0 is mainly produced by its reaction with 03.A small deviation from the linearity discernible near the origin suggests that only a part of the products is converted into the aerosol in the initial stage of the reaction. According to the study by Hatakeyama et al. (IO), the primary products of the gas-phase C6H10 + O3reaction are a,w-dialdehydesand w-oxo-a-carboxylicacids. Among them, the aldehydes have vapor pressures so high (probably of the order of lo4 atm, or a few ppm) that they hardly contribute to the aerosol formation in the condition corresponding to Figure 6. In other words, when the initial concentration of is in the sub-ppm range, the amount of aldehydes does not reach a level required to attain supersaturation. However, the oxo acids, which should have lower vapor pressures, behave differently: They remain in the gas phase immediately after being produced, but with a certain lapse of time, they nucleate and grow into particles detectable by the EAA. ConseEnviron. Sci. Technoi., Vol. 22, No. 10, 1988
1211
quently, the aerosol volume concentration, V, is first below the value corresponding to the reacted amount of CGH10 and then becomes proportional to it in the later stages. This reasoning explains the downward deviation from the linearity shown in Figure 6. Therefore, by leaving out the data in a region kl~~[C6H10][03] dt 0.04 ppm, a line passing through the origin was fitted to the curve in Figure 6. The slope of the line thus obtained was considered to represent the volume-basis aerosol yield per unit loss of the hydrocarbon due to the reaction with 03.The slope value with 2a came out to be 415 f 33 pm3 cm-3 ppm-l. Three other runs were conducted with essentially the same condition, and the average yield on the basis of the four runs turned out to be 417 f 11 pm3 ~ m - ~ . Contribution of the Hydroxyl Radical. In the preceding section, it was shown that the aerosol formation from C6H10 is most likely due to its reaction with 03. However, as stated in the Introduction, OH is another species that reacts with in the present reaction system, and no other species contributes significantly to the depletion of CBH1,). Therefore, the depletion rate of C&lo is expressed as
where kl and k 2 are the rate constants for the reactions of CGH10 with O3and OH, respectively. The rate constant kl was determined in this study as previously described; k, has been reported by Wu et al. (25) to be 6.24 X cm3molecule-l s-l at 303 K, being in good agreement with other literature values (12,26,27). By using those kl and k2 constants, and by measuring the time variation of C6H10 and O3 concentrations, the concentration of OH was calculated through eq 2 (28). I t was found in consequence that [OH] reached a value of 3.2 X lo6 molecule cm-3 (1.3 X ppm) at 20 min, when O3formation rate was also maximum. The peak concentration is similar to those reported for other photoirradiated systems (28-30). The concurrence of the peaks in [OH] and d[03]/dt was also observed in the experiment of Sakamaki et al. (28). In the case shown in Figure 4, the portion of C6H10 reacted with OH was calculated to be 45% of the total consumption of the hydrocarbon. In order to assess the contribution of the + OH reaction to the overall aerosol formation, the aerosol yield from this reaction was determined separately. For this purpose, C&lo was made to react with OH, which was generated by the photolysis of CH30N0 (11, 12). In 20 min of the reaction, the total volume concentration (V)of the aerosol product attained a value of 3.8 pm3 ~ m -while ~, the corresponding decrement in C&10 concentration was 0.76 ppm. Consequently, the aerosol yield from unit concentration of CsHlo was calculated to be 5.0 pm3 cm-3 ppm-l. Several more runs were made, and similar values for the yield were obtained within a fluctuation of a few pm3 cm-3 ppm-l. As expected, the aerosol yield from the + OH reaction was found to be as small as of the yield from the C&10 O3 reaction. This result leads to a conclusion that, although the substantial portion of CGHlo is consumed by the reaction with OH, most of the reaction products remain in the gas phase and hardly contribute to the aerosol formation. Thus, it is confirmed that the C6H10 + O3 reaction is the one responsible for the aerosol formation in the present reaction system. Aerosol Organic Carbon and Nitrogen Contents. As stated earlier, the experiments for the AOC determination were conducted with higher C6Hlo initial concentrations and with different reaction time, In each experiment, the aerosol was sampled several times during the irradiation
+
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Environ. Sci. Technol., Vol. 22, No. 10, 1988
Figure 7. Aerosol organic carbon concentration per unit volume of air vs the amount of C,H, reacted with 03. Table 111. Aerosol Yield from C6H10 Basis of Carbon Mass
run no.
[C6H10], ppm
1 4.81 2 4.93 3 5.17 4 10.2 5 9.90 average yield
init condn [NO], [NO,], ppm ppm 0.45 0.44 0.50 0.87 0.84
0.70 0.61 0.58 1.45 1.44
carbon-basis percent conversion*
+ O3 Reaction on t h e carbon-basis -2-12 0
Yla'u,-
RH, %
4.6 30 53 30 30
-
of C m-3 ppm-' (CGH1O) 555 f 178 538 f 454 646 f 1370 493 f 528 512 f 138 528 f 104 18.3 f 3.6
"Obtained from the slope of the plot of AOC concentration vs the amount of C&lo reacted with O3(Figure 7). *Calculated from the average yield by considering that 1 ppm of CsHlo at 303 K and 1 atm is equivalent to a carbon mass concentration of 2890 pg of C m-3.
and was analyzed for AOC; the carbon content per unit volume of air obtained in one of the runs is plotted in Figure 7 against the amount of CGHlo reacted with 03.A line was fitted to the six data points to obtain the aerosol carbon mass yielded from unit concentration of C6H10. From the slope of the line, the carbon-basis yield was determined to be 555 f 178 pg of C ppm-l. Table I11 is a summary of the results obtained from all runs. The slope was thus found to be independent of both the initial concentration of the reactants and RH. The average slope value was calculated to be 528 f 104 pg of C m-3 ppm-l, and this is equivalent to 18.3 f 3.6% conversion of carbon in CGH10 into the particle form. The range of uncertainty corresponds to twice the standard deviation derived from the data for five runs shown in Table 111; the uncertainty due to that in kl is much smaller. The percent conversion determined here agrees with 13 f 3% reported by Hatakeyama et al. (10) within the error ranges. As mentioned in the Experimental Section, there was found a proportional relation between V, and [AOC]. A specific expression for the relation was [AOC] = kVd (3) with the proportionality constant k being 0.49 f 0.02 g of C ~ m - ~Using . this relation one can calculate the volume-basis yield that is equivalent to the average carbonbasis yield given above. The result comes out to be 1078 f 212 pm3 cm-3 ppm-l. An additional experiment was conducted to determine the AON concentration under a condition similar to that in run 1. The AON found in the aerosol sample was 21 pg of N m-3 at the end of the irradiation. Since the concentration of AOC at the same time is estimated to be 1400 pg of C m-3 from Figure 7, the ratio of [AON] to [AOC] is as low as 0.015. If the condensed products are composed of mononitrates with six carbons in a molecule, the molar
m
'6
400
m
i
-I 300 I
v
u
'I
I
/
I
1
2 200-
>r"
c
1
5 E -0.1 5 -0.2
-
Ya 100-
%
I
0
'v! 10
I
20
10 RH
30
40
50
(X)
Flgure 9. Humidity dependences of the volume-basis aerosol yield (the upper curves) and dp measured at the end of the irradiation (the lower curve), Solid circles in the upper curve denote the yield calculated on the basis of V,; [C,H,,lo was 0.3 ppm.
RH
( %)
Flgure 8. (a) Dependence of the maximum concentratlon of condensation nuclei C ([ N),] on relative humidity; (b) humidity dependence of the maximum growth rate of [CN] [(d[CN]ldt),]. Open and solid circles are the results from the experiments with [C6H10]0= 1.0 and 0.3 ppm, respectively.
ratio of the products with and without nitrogen should be 1:12. Thus, the nitrogenous compounds were found to be minor products. This is ascribable to the low NOJHC ratio employed in this study. In fact, Grosjean and Friedlander (8),who conducted the photoirradiation experiments with a higher NO,/HC ratio than in this study, reported that 6-nitratohexanoic acid was one of the two major products. Possible pathways to nitrogenous species are reactions of NO, with the Criegee intermediate, which is formed by the reaction between C6HIo and Os. On the other hand, it is clear that OH radicals do not contribute to the formation of the nitrogenous aerosol even in the case of high NOJHC ratios, since little aerosol was found to be formed from the OH C6HIo reaction, which was conducted with excess NO. Humidity Effects on Aerosol Formation. The effects of humidity on the aerosol formation processes were examined by the experiments with different RH ranging from 10 to 50%. The initial concentration of C&10 was set equal to 0.3 or 1ppm. The data obtained from the CNC measurements are illustrated in Figure 8, parts a and b. Figure 8a is a plot of the maximum concentration of condensation nuclei ([CN],,,) against RH. It is seen that [CN], increases steeply with increasing RH when the RH >30%. There is no significant difference in the RH dependence of [CN],, observed for the two different initial concentrations of C6HIo. In Figure 8b is shown the dependence of the maximum increasing rate of condensation nuclei [(d[CN]/dt),,] on RH. The general appearance of the humidity dependence is similar to that in Figure 8a, but the maximum rate observed for the higher initial concentration of C6Hlo has significantly stronger dependence than the rate for the lower concentration. The humidity effect on the volume-basis aerosol yield was derived from the EAA measurements as shown in Figure 9 (the upper solid curve). The error bars for the data for RH I40% represent two standard deviations obtained in the least-squares analysis for determining the yield. The data for RH = 50% are an average of four
+
Flgure 10. Dependences of [CN], (solid circles) and (d[CN]ldt), (open circles) on the initial concentration of C6Hlo.
determinations. The yield is found to increase significantly when RH exceeds 40%. However, if the volume-basisyield is calculated from v d instead of V , it turns out to be independent of RH as shown by the broken line in Figure 9. This behavior parallels that of the carbon-basis yield, which was also shown to be independent of RH as described in the preceding section. From these observations it can be concluded that v d obtained with dry sheath air corresponds to the net volume of the organic constituents in the aerosol particles and that the increase in the volume-basis yield for RH I40% is caused by intake of H20 into the aerosol particles. A ratio of Vd to V thus can be regarded as a volume fraction of organic matter in the aerosol particles under a condition of given RH. From Figure 9, the fraction for RH 50% is found to be 0.73. It is likely that there exists a strong interaction between the organic aerosol components and H20vapor, and such an interaction accelerates the heteromolecular nucleation (31) when the RH is high. This inference is consistent with the observation of the increase in (d[CN]/dt),, in the higher RH region (Figure 8b). The number-basis geometric mean diameter, which was measured at the end of the irradiation, is also plotted in Figure 9 against RH (the lower curve). It is observed that the particle sizes are constant at 0.12 pm for RH < 30% but decrease as RH exceeds 40%. The decrease in the size is attributable to the steep increase in the particle number concentration occurring in the same RH region (Figure 8a). Effects of Initial Concentration of Cyclohexene on Aerosol Formation. Experiments were carried out with different C6Hlo initial concentrations ([ C6Hl,J0) in order to look into the effect of varying the hydrocarbon initial concentration. The relative humidity was held constant at 30%. In Figure 10, the [CNI,,, and (d[CN]/dt),,, observed in these experiments are plotted against [c6Hlo],. The maximum CN concentration was found to be almost insensitive to the initial concentration, while the maximum increasing rate steeply rose as [C6HloIO increased up to 2 Environ. Sci. Technoi., VoI. 22, No. 10, 1988 1213
[C,H,olo
(PPm)
Figure 11. Dependence of the volume-basis aerosol yield on the Intiai concentration of C,H,,.
ppm but leveled off in the higher initial concentration region. The effect on the volume-basis yield is shown in Figure 11. The value 947 f 85 pm3 cm-3 ppm-l for [C6H10]0= 5 ppm is in fair agreement with the value 1078 f 212 calculated from the average carbon-basis yield given in Table 111. Since the carbon- and volume-basis yields are proportional to each other, one can see from the data shown in Table I11 that the latter yield stays essentially constant for the range 4.8 < [C6H10]0< 10.2 ppm. In contrast, the yield was found to decrease nonlinearly when [C6H10]0was decreased below 1 ppm. A qualitative explanation for this phenomenon is as follows: When the initial concentration of C6H10 is higher than a few ppm, concentrations of the products are accordingly high. As a result, supersaturation is attained even for a,w-dialdehydes and they contribute to the aerosol formation as well as w-oxo-a-carboxylicacids. However, when [C6Hl0I0 is decreased to be less than, say, 1 ppm, the concentrations of the aldehydes no longer satisfy the condition for supersaturation, causing the lowering of the aerosol yield. The result shown in Figure 11 thus gives a warning that an extrapolation of the data obtained in high-concentration experiments to a lower concentration region may cause a serious error. Since the concentrations of cycloalkenes in the actual atmosphere are at most a few hundredths ppm, it is of particular importance to determine accurately the aerosol yield with such low initial concentrations. Anyway, it is inferred from Figure 11 that the volume concentration of the aerosols produced by the photochemical reactions in the actual atmosphere is as low as 100 pm3 cmm3/lppm of C6H1,) Major reaction products are considered to be aldehydes, which remain in the gas phase. Since those aldehydes are likely to be subsequently degraded into compounds of less carbon numbers through reactions with OH or photolyses (32), there is little possibility of secondary aerosol generation from the aldehydes.
Summary and Conclusions By using a 4-m3 chamber, photochemical aerosol formation from a mixture of C6Hlo and nitrogen oxides was investigated with the main purpose of determining the aerosol yield, for which little data are currently available. Prior to the main irradiation experiments, the rate constant for the reaction of C6Hlowith O3 was found to be 0.144 f 0.003 ppm-l min-' at 303 f 1 K. In addition, it was shown that, in the determination of carbon content by filter sampling, the artifact caused by adsorption of vapor-phase organics on quartz filters should not be neglected. Principal results obtained in the main experiment are itemized as follows: (1) Aerosol particles are formed exclusively by the reaction of C&lo with 03,while the products of the reaction with OH have no contribution to the aerosol formation. 1214
Environ. Sci. Technol., Vol. 22, No. 10, 1988
(2) The aerosol yield on the basis of carbon mass is as much as 18% in a C&o initial concentration range of 5-10 PPm. (3) However, the yield decreases by an order of magnitude as the initial concentration of C6HIo is decreased below 1 ppm. (4) The aerosol yield on the basis of aerosol volume concentration increases significantly for RH 1 40% because of the intake of water into the particles, whereas the carbon-based yield is independent of RH. The third result has particular importance in assessing the contribution of C6Hlo to the organic aerosol formation in the environment. Accordingly, further investigation should be done in a lower concentration range typical of the actual atmospheric condition.
Acknowledgments We are grateful to K. Sakamoto of Saitama University for his cooperation in determining the aerosol organic carbon concentrations and to S. Hatakeyama of the National Institute for Environmental Studies for offering the data on cyclohexene-ozone reaction before publication. Assistance given by T. Hayano of Nihon Kagaku Kogyo Co. in the chamber experiments is also acknowledged. Registry No. AOC, 7440-44-0;AON, 7727-37-9;CBHIO, 11083-8; NO, 10102-43-9; NOz, 10102-44-0; HO., 3352-57-6; Os, 10028-15-6.
Literature Cited (1) Grosjean, D.; Cauwenberghe, K. V.; Schmid, J. P.; Kelly, P. E.; Pitts, J. N., Jr. Environ. Sci. Technol. 1978, 12, 3 13-3 17. (2) Schuetzle, D.; Cronn, D.; Crittenden, A. L. Enuiron. Sci. Technol. 1975,9,838-845. (3) Cronn, D. R.; Charlson, R. J.; Knights, R. L.; Crittenden, A. L.; Appel, B. R. Atmos. Environ. 1977, 11, 929-937. (4) Appel, B. R.; Hoffer, E. M.; Kothny, E. L.; Wall, S. M.; Haik, M.; Knights, R. L. Enuiron. Sci. Technol. 1979,13,9&104. (5) Appel, B. R.; Wall, S. M.; Knights, R. L. Adv. Enuiron. Sci. Technol. 1979, 9, 353-365. (6) Kocmond, W. C.; Yang, J. Y.; Kittelson, D. B.; Whitby, K. T.; Demerjian, K. L. Adv. Enuiron. Sci. Technol. 1977, 8(Part 2), 101-135. (7) Heisler, S. L.; Friedlander,S. K. Atmos. Environ. 1977,11, 157-168. (8) Grosjean, D.; Friedlander, S. K. Adv. Enuiron. Sci. Technol. 1979,9,435-473. (9) Grosjean, D. In Ozone and Other Photochemical Oxidands, National Academy of Sciences;National Research Council: Washington, DC, 1977; pp 45-125. (10) Hatakeyama, S.; Tanonaka, T.; Weng, J.; Bandow, H.; Takagi, H.; Akimoto, H. Enuiron. Sci. Technol. 1985,19, 935-942. (11) Atkinson, R.; Aschmann, S. M.; Winer, A. M.; Pitts, J. N., Jr. Int. J. Chem. Kinet. 1982, 14, 507-516. (12) Atkinson, R.; Aschmann, S. M.; Carter, W. P. L. Int. J. Chem. Kinet. 1983, 15, 1161-1177. (13) Izumi, K.; Mizuochi, M.; Yoshioka, M.; Murano, K.; Fukuyama, T. Enuiron. Sci. Technol. 1984, 18, 116-118. (14) Izumi, K.; Mizuochi, M.; Murano, K.; Ozaki, Y.; Fukuyama, T. Int. J. Environ. Stud. 1986,27, 183-199. (15) McMurry, P.H.; Friedlander, S.K. J. Colloid Interface Sci. 1978, 64, 248-257. (16) Sem, G. J.; Agarwal, J. K.; McManus, C. E. In Aduances in Particle Sampling and Measurement;U.S. Government Printing Office: Washington, DC, 1979; EPA-600/9-80-004, pp 276-301. (17) Wolff, G. T.; Klimisch, R. L. In Particulate CarbonAtmospheric Life Cycle; Plenum: New York, 1982; pp 79-129. (18) Cadle, S. H.; Globlicki, P. J.; Mulawa, P. A. Atmos. Environ. 1983, 17, 593-600.
Environ. Sci. Technol. 1988, 22, 1215-1219
Appel, B. R.; Haik, M.; Kothny, E. L. Atmos. Environ. 1984, 18, 409-416. Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.; Pitts, J. N., Jr. Int. J. Chem. Kinet. 1983,15,721-731. Cadle, R. D.; Schadt, C. J. Am. Chem. SOC.1952, 74, 6002-6004. Japar, S. M.; Wu, C. H.; Niki, H. J.Phys. Chem. 1974, 78, 2318-2320. Adeniji, S. A.; Kerr, J. A.; Williams, M. R. Int. J. Chem. Kinet. 1981, 13, 209-217. Husar, R. B.; Whitby, K. T. Environ. Sci. Technol. 1973, 7, 241-247. Wu, C. H.; Japar, S. M.; Niki, H. J. Enuiron. Sci. Health, Part A 1976, A l l , 191-200. Ohta, T. J. Phys. Chem. 1983,87, 1209-1213.
(27) Darnall, K. R.; Winer, A. M.; Lloyd, A. C.; Pitts, J. N., Jr. Chem. Phys. Lett. 1976,44,415-418. (28) Sakamaki, F.; Akimoto, H.; Okuda, M. Environ. Sci. Technol. 1981,15,665-671. (29) Carter, W. P. L.; Atkinson, R.; Winer, A. M.; Pitts, J. N., Jr. Int. J. Chem. Kinet. 1982, 14, 1071-1103. (30) Grosjean, D. Sci. Total Environ. 1984, 37, 195-211. (31) Friedlander, S. K. In Smoke, Dust and HazeFundamentalsof Aerosol Behavior;Wiley: New York, 1977; pp 243-246. (32) Atkinson, R. Chem. Rev. 1985, 85, 69-201.
Received for review March 26,1987. Revised manuscript received March 1, 1988. Accepted March 22, 1988.
Sequential Degradation of Chlorophenols by Photolytic and Microbial Treatment Raina M. Miller,t George M. Singer,$ Joseph D. Rosen,b and Richard Bartha*vt Department of Biochemistry and Microbiology and Department of Food Science, Cook College, Rutgers University, New Brunswick, New Jersey 08903
w Using the radiolabeled model pollutants 2,4-dichlorophenol (DCP) and 2,4,5-trichlorophenol (TCP) we demonstrated that brief UV (300-nm) photolysis greatly facilitates the removal of the two chlorophenols from sewage through accelerated mineralization and binding of polar products. The addition of 0.1 M HzOzstrongly accelerated the photolysis process resulting in half-lives of 1.68 and 0.87 min for DCP and TCP, respectively. In natural sunlight, half-lives of the chlorophenols were less than 1 day when H20zwas present. During 4 days of incubation in activated sewage sludge, only 3% of unphotolyzed DCP and 1% of unphotolyzed TCP were mineralized. Mineralization rose to 79 and 59%, respectively, after photolysis in the presence of Hz02 Photolysis without H202resulted in removal of chlorophenols from solution chiefly by binding. Increased mineralization and binding were observed also upon incubation of photolyzed chlorophenols in soil. Disruption of carbon-halogen bonds by brief photolysis followed by traditional biological effluent treatment offers an alternative to activated charcoal treatment for removal of xenobiotics from industrial effluents. Introduction
Halo-substituted aromatics occur rarely in natural products but have gained notoriety as environmental pollutants that are resistant to biodegradation (1). Consequently, conventional biological waste treatment is ineffective, and removal from industrial effluents by activated carbon absorption is commonly used (6). Frequent need for carbon reactivation renders this process both inconvenient and costly. The carbon-halogen bonds that prevent or delay biodegradation are, however, susceptible to photolytic cleavage. Unfortunately, total removal of halo aromatics by photolysis is also costly. Economic and mode of action considerations suggested that partial photolysis might prime recalcitrant halo aromatics for subsequent biodegradation. A sequential treatment pro-
'*Department Department of Biochemistry and Microbiology. of Food Science. 0013-936X/88/0922-1215$01.50/0
cess using a relatively brief photolysis period followed by conventional biological waste water treatment may offer both technical and economic advantages. To explore this concept, 2,4-dichlorophenol (DCP) and 2,4,5-trichlorophenol (TCP) were photolyzed with and without added Hz02as a source of hydroxyl radicals. Biodegradation of intact and photolyzed compounds to 14C02and to polar and to bound metabolites was compared. Experimental Section
Photolysis. Uniformly 14C-ring-labeledDCP (sp act. 2.9 mCi/mmol) and TCP (sp act. 9.0 mCi/mmol) were obtained from Pathfinder Laboratories, St. Louis, MO. Their radiochemical purity was determined by thin-layer chromatography using a solvent sytem of hexane:acetone (4:l) on silica gel plates and was found to be 98% for both DCP and TCP. Aqueous solutions (100 pg/mL, w/v) of DCP (1.49 X lo6 DPM/mL) and of TCP (6.32 X lo4 DPM/mL) were irradiated in a Rayonet "merry-go-round" photochemical reactor (Southern New England Ultraviolet Co., Hamden, CT) by using RPR 3000-A lamps. These lamps emit light between 270 and 350 nm with a maximum at 300 nm. There are also small contributions at 248-258, 360-370, 400-410, 430-440, 520-530, and 572-582 nm. Incident intensity, as measued by potassium ferrioxalate actinometry (4), was 4.63 pE m-2 s-l. Prior to irradiation of 14C-labeledmaterial, studies were conducted with aqueous solutions (100 pg/mL) of unlabeled chlorophenols using either the photoreactor or sunlight. These irradiations were conducted in the presence of 0-0.1 M H202. At selected time intervals, 2-pL aliquots of the irradiated chlorophenol solutions were assayed on a Tracor 550 gas chromatograph equipped with FID and a 30 m X 0.53 mm DB-17 vitreous silica megabore capillary column (J & W Scientific, Folsom, CA). A cold on-column injector was used. The oven temperature was kept at 70 "C for 2 min, reset to 110 OC for 2 min, and subsequently programmed to 250 "C at 5 "C/min. Helium carrier gas flow was 12 mL/min. Quantitation was by the external standard method. H202(50%),17.54 M by iodometric titration (B), was added to some of the chlorophenol solutions to give
0 1988 American Chemical Society
Environ. Sci. Technol., Vol. 22, No. 10, 1988 1215
