Environ. Sci. Technol. 1990, 24, 144-146
where residual petroleum is present. The sorptive behavior of residual PCB oil (commercial Aroclor) in a PCB-contaminated soil was also evaluated by using the soil denoted PP (Table I). To obtain the predicted K values, the PCB oil-water partition coefficient was again estimated as being approximately equal to KO, (Table 11). This assumption appears valid for toluene where the measured sorption coefficient (Table 111, obtained from the slope of the linear isotherm (Figure l),was in excellent agreement with the predicted value. However, for 2-chlorobiphenyl, use of Kowto approximate the PCB oil-water partition coefficient underestimated the observed K (Figure 1 and Table 11). The measured K value for 2-chlorobiphenyl corresponds to a log Kofivalue of -5 (log KO, = 4.51) and this is entirely reasonable because 2chlorobiphenyl would be expected to form a more nearly ideal solution in PCB oil than in octanol, making KO,> Kow.In fact, a plot of log Kowversus water solubility for various organic compounds shows that 2-chlorobiphenyl falls below the ideal line by -0.7 log unit (11). Thus, the sorptive behavior of residual PCB oils appears similar in nature to that of residual petroleum. However, in the case of sorption of individual PCB congeners by residual PCB oils, nearly ideal solution behavior is observed and KO,will be greater than Kow;the magnitude of this difference will increase for the more heavily chlorinated PCB congeners (11). The resulting effect of residual PCB oils on the soil-water distribution coefficient is dramatic; the K value predicted in the conventional manner, where only soil organic matter is acting as a sorptive phase, is -37, whereas the observed value is 702. These results demonstrate that residual petroleum and PCB oils present in soil act as highly effective partition media for organic contaminants. The presence of these highly sorptive anthropogenic organic phases in soils and sediments will significantly increase the immobilization of organic contaminants and thus strongly influence their environmental fate and behavior. The observed soil-water distribution coefficients of organic contaminants were accurately predicted from the soil organic matter content, the oil content (expressed as oil/grease or PCB content), and the solute Komand Kowvalues. The magnitude of the oil-water partition coefficient makes the residual oil phase a significant sink for organic contaminants in these systems. For accurate prediction of soil-water distribution coefficients in such soils and sediments, the oil compo-
nents, along with the natural organic matter component, must be measured and accounted for individually. The limited effectiveness of soil washing and pump and treat technologies (12, 13) for remediating soils contaminated by petroleum spills and PCBs may be related in part to the sorptive behavior of residual oil components as described here. Acknowledgments
We thank Dr. John Quensen, 111, for the PCB analyses and helpful discussions. Literature Cited (1) Chiou, C. T.; Peters, L. J.; Freed, V. H. Science 1979,206, 831-832. (2) Chiou, C. T.; Porter, P. E.; Schmedding, D. W. Environ. Sci. Technol. 1983, 17, 227-231. (3) Karickhoff, S. W.; Brown, D. S.; Scott, T. A. Water Res. 1979,13,241-248. (4) Chiou, C. T. In Reactions and Movement of Organic Chemicals in Soils;Sawhney, B. L., Brown, K., Eds.; Special Publication No. 22; Soil Science Society of America: Madison, WI, 1989; pp 1-29. (5) Mikesell, M. D.; Boyd, S. A. Environ. Sci. Technol. 1988, 22, 1411-1414. (6) Quensen, J. F., 111; Tiedje, J. M.; Boyd, S. A. Science 1988, 242, 752-754. (7) Cirelli, D. P. In Pentachlorophenol: Chemistry, Pharmacology and Environmental Toxicology;Rao, K. R., Ed.; Plenum: New York, 1978; pp 13-18. (8) Bartha, R. Microb. Ecol. 1986, 12, 155-172. (9) Schellenberg, K.; Leuenberger, C.; Schwarzenbach, R. P. Enuiron. Sci. Technol. 1984, 18, 652-657. (10) Lagas, P. Chemosphere 1988, 17, 205-216. (11) Chiou, C. T.; Schmedding, D. W. Enoiron. Sci. Technol. 1982, 16, 4-10. (12) Mackay, D. M.; Cherry, J. A. Environ. Sci. Technol. 1989, 23,630-636. (13) Bouchard, D. C.; Enfield, C. G.; Piwoni, M. D. In Reactions and Movement of Organic Chemicals in Soils; Sawhney, B. L., Brown, K., Eds.; Special Publication No. 22; Soil Science Society of America: Madison, WI, 1989 pp 349-371. Received for review September 14,1989. Accepted October 30, 1989. Partial support from the US.Environmental Protection Agency un,der Grant R-815750-01-0, BioTrol, Inc., and the Michigan Agricultural Experiment Station.
Ambient Formic Acid in Southern California Air: A Comparison of Two Methods, Fourier Transform Infrared Spectroscopy and Alkaline Trap-Liquid Chromatography with UV Detection Danlel Grosjean,*-t Ernest0 C. Tuazon,t and Eric Fujltag DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, California 93003, Statewide Air Pollution Research Center, University of California, Riverside, Callfornia 92521, and Research Division, California Air Resources Board, P.O. Box 2815, Sacramento, California 95812
Introduction
Formic acid is an ubiquitous component of urban smog. Sources of formic acid in urban air include direct emissions from vehicles (1)and in situ reaction of ozone with olefins (2). Ambient levels of formic acid in southern California air were first measured some 15 years ago by Hanst et al. 'DGA, Inc. f
University of California.
f
California Air Resources Board.
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(3) using long-path Fourier transform infrared spectroscopy (FTIR). All subsequent studies of formic acid in the Los Angeles area have involved the use of two methods, either FTIR (4-6) or collection on alkaline traps followed or by gas chromatography (I), ion chromatography (9, liquid chromatography analysis with UV detection, ATLC-UV (2,8). The Carbon Species Methods Comparison Study (CSMCS), a multilaboratory air quality study carried out in August 1986 at a southern California smog receptor site
0013-936X/89/0924-0144$02.50/0
0 1989 American Chemical Society
Table I. Regression Parameters"
no. of observations degrees of freedom slope f SE intercept f SE X - Y , mean f 1 SD R2 a
all data
excluding 8/15, 0-8 a.m. outlier
39 37 0.95 f 0.15 0.10 & 1.68 0.13 & 1.64 0.512
38 36 1.07 f 0.13 -0.59 & 1.42 0.28 f 1.39
12
,
. - - ATLC-UV
0.645
Y , alkaline trap method; X, FTIR method; units, ppb.
(9),provided an opportunity for direct field comparison of the FTIR and alkaline trap methods. The results of the comparison are presented in this brief report. To our knowledge, no interlaboratory comparison of ambient formic acid measurements involving entirely different sampling and analytical methods has been carried out prior to this work. Results of a comparison of sampling methods for ambient formic acid (all participants employed the same analytical method, i.e., standard ion chromatography) have been recently reported (10). Measurement Methods Only a brief description of the methods employed is given below. More detailed accounts can be found elsewhere (2, 11). All measurements were carried out on August 12-21, 1986, in Glendora, CA, 35 km east of Los Angeles, on the Citrus College campus. The alkaline trap sampling units were located on a platform and sampled air 2.5 m above the ground. The FTIR instrument employed on open 25 m base-path multiple-reflection optical system, whose optical axis was also 2.5 m above the ground, parallel to and -15 m upwind of the platform. The FTIR spectra were recorded a t a total path length of 1150 m and a resolution of 0.13 cm-l. Formic acid was measured by its absorption at 1105.0 cm-' after correcting for the interference by a weak absorption band of water. The FTIR calibration was essentially a determination of the 1105-cm-' absorptivity a t the actual resolution of the spectrometer. This calibration, which obeyed BeerLambert's law, was carried out in the laboratory with ppm concentrations of HCOOH monomer generated in a 5870-L evacuable chamber equipped with long-path optics (11). At the resolution and path length employed, the detection limit was 1 ppb and the estimated precision was 1.5 ppb. Alkaline traps consisted of KOH-impregnated 47 mm diameter glass fiber filters mounted downstream of 1.2 pm pore size Teflon filters in open-face dual-filter holders and connected to a calibrated flow meter and a sampling pump. The sampling flow rate was 14 L/min. After sampling, the filters were promptly placed in glass vials capped with Teflon-lined screw caps and containing 10 mL of deionized water and 40 pL of chloroform added as a biocide. Following filter sonication for 10 min in their individual glass vials, aqueous extracts were analyzed by liquid chromatography with a size exclusion column, dilute H2S04eluent, and ultraviolet detection as is described elsewhere (2). Calibration involved the use of external standards, Le., aqueous solutions of formate whose concentrations bracketed those relevant to the ambient air samples. Calibration plots (peak height vs concentration) were linear with near-zero intercepts, relative standard deviations on the slope of f5%, and correlation coefficients of 20.99. Collection efficiency was verified with two alkaline filters in series and was 0.89 f 0.07 for 18 field samples. The detection limit was 0.29 ppb (4-h samples) and 0.15 ppb (8-h samples) and the estimated precision was fl ppb for
0
I,,,,,(,,,,,,,,,, 8/12
8/13
8/14
8/15
, 8/16
8/17
8/10
8/19
WM
8121
Date
Figure 1.
Ambient levels of formic acid, Glendora, CA, August methods.
12-21,
1986, measured by the FTIR and ATLC-UV
HCOOH of 5 5 ppb and *15% for HCOOH of >5 ppb. Results and Discussion The comparison was carried out in a "blind" mode, with both groups reporting their respective results to the California Air Resources Board without prior knowledge of each other's data. The alkaline trap samples were collected according to a CMSCS-prescribed schedule of five consecutive samples per day, one 8-h sample starting at midnight and four 4-h samples thereafter. FTIR data points, each corresponding to a measurement time of 5 min and initially reported every -15-20 min and as hourly averages ( I I ) , were averaged here over time periods corresponding to those of the 44 alkaline trap samples. Of these, five were excluded due to insufficient FTIR data, yielding 39 FTIR averages. Time series of ambient formic acid measured by FTIR and by the alkaline trap-liquid chromatography method are plotted together in Figure 1,which indicates reasonable agreement with respect to both ambient concentrations and diurnal variations. Regression parameters are given in Table I for the entire data set, with and without the single outlier observation of August 15,O:OO-8:00 PDT. There is no significant bias, and the mean difference between the two methods is comparable to the stated precision of the measurements. Our study, although limited, encompassed a range of conditions (temperature, humidity, levels of copollutants such as ozone, aldehydes, nitric acid, peroxyacetyl nitrate, etc.; see ref 2 for details) that are representative of summertime air quality in southern California. The reasonable agreement between the two methods lends additional confidence in the reliability of formic acid data obtained by both FTIR and ATLC-UV during CSMCS, as well as in data from earlier studies, all involving either FTIR or alkaline trap methods, of ambient levels of formic acid in southern California. Acknowledgments We thank D. R. Lawson (ARB) and the CSMCS participants for their support. Literature Cited (1) Kawamura, K.; Ng, L. L.; Kaplan, I. R. Enuiron. Sci. Technol. 1985,19, 1082. (2) Grosjean, D.; Williams, E.; Van Neste, A. Measurements
of organic acids in the South Coast Air Basin. Final report to the California Air Resources Board, Agreement A5177-32, DGA, Inc., Ventura, CA, 1988. Environ. Sci. Technol., Vol. 24, No. 1, 1990 145
(3) Hanst, P. L.; Wilson, W. E.; Patterson, R. K.; Gay, B. W.; Chaney, L. W.; Burton, C. S. A spectroscopic study of California smog. U S . EPA report, EPA 650/4-75-006; Research Triangle Park, NC, 1975. (4) Tuazon, E. C.; Winer, A. M.; Graham, R. A.; Pitts, J. N., Jr. Adv. Enuiron. Sci. Technol. 1980, 10, 259. (5) Tuazon, E. C.; Winer, A. M.; Pitts, J. N., Jr. Environ. Sci. Technol. 1981, 15, 1232. (6) Hanst, P. L.; Wong, N. W.; Bragin, J. Atmos. Environ. 1982, 16, 969. (7) Grosjean, D. Atmos. Environ. 1988, 22, 1637. (8) Grosjean, D. Measurements of low molecular weight carboxylic acids during the Southern California Air Quality Study. Final report to the Coordinating Research Council,
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Project CRC-SCAQS-2, DGA, Inc. Ventura, CA., 1988. (9) Lawson, D. R.; Hering, S. V. Aerosol Sci. Technol., in press. (10) Keene, W. C.; et al. J. Geophys. Res. 1989, 94, 6457. (11) Tuazon, E. C. Derivation of formic acid data from FTIR spectra recorded during the 1986 Carbonaceous Species Methods Comparison Study. Final report to the California Air Resources Board, Contract A733-167, U. of California, Riverside, CA, 1989.
Received for review August 29,1989. Accepted October 30,1989. The measurements on which this communication is based have been sponsored by the California Air Resources Board (ARB), Agreements A5-177-32 and A733-167.
