Environ. Sci. Technol. 1992, 26, 744-749
Jeong, K.-M.; Kaufman, F. J . Phys. Chem. 1983, 86, 1816-1821. The CRC Handbook of Chemistry and Physics, 69th ed.; Weast, R. C., Ed.; Chemical Rubber Company: Boca Raton, FL, 1989. Cohen, N. StructureReactivity Relationships for Predicting Environmentally Hazardous Chemicals. EPA-600/3-86/ 672; U.S.Government Printing Office: Washington, DC, 1986; p 41. Hinze, J. L. Number Cruncher Statistical System (NCSS), Version 5.0, Kaysville, UT, 1987. Hendry, D. G.; Kenley, R. A. Atmospheric Reaction Products of Organic Compounds. EPA-560/ 12-79-001;U.S. Government Printing Office: Washington, DC, 1979. Evans, M. G.; Polanyi, M. Trans. Faraday Sac. 1938,34, 11. Johnston, H. S,; Parr, C. J. Am. Chem. Sac. 1963,85,2544. Johnston, H. S. Gas Phase Reaction Rate Theory; Ronald Press: New York, 1966; p 339. Gaffney, J. S.;Levine, S. Z. Int. J. Chem. Kinet. 1979,11, 1197-1209.
Atkinson, R. Int. J . Chem. Kinet. 1980,12,761-765. Cohen, N. I n t . J . Chem. Kinet. 1982,14,1339-1362. Darnall, K.R.; Atkinson, R.; Pitts, J. N., Jr. J. Phys. Chem. 1978,82,1581-1584. Greiner, N. R. J. Chem. Phys. 1970,53,1070-1076. Baldwin, R. R.; Walker, R. W. J. Chem. SOC.,Faraday Trans. 1 1978,75,140-155. Shaw, R. J . Phys. Chem. Ref. Data 1978, 7, 1179-1190. Perry, R. A,; Atkinson, R.; Pitts, J. N., Jr. J. Chem. Phys. 1976,64, 1618-1620. Heicklen, J. Int. J . Chem. Kinet. 1981,13,651-665. Egger, K.W.; Cocks, A. T. Helv. Chim. Acta 1973,56, 1537-1553. Zavitsas, A. A. J . Phys. Chem. 1987,91,5573-5577. Truhlar, D. G.; Schwenke, D. W.; Kouri, D. J. J. Phys. Chem. 1990,94,7346-7352. Benson, S. W. Thermochemical Kinetics, 2nd ed.; John Wiley and Sons: New York, 1976; pp 10-13. Received for review April 3,1991.Revised manuscript received September 4, 1991. Accepted December 2, 1991.
Passive Ozone/Oxidant Sampler with Coulometric Determination Using I,/Nylon-6 Charge-Transfer Complex Seiichiro Kannot and Yukio Yanagisawa" Harvard School of Public Health, 665 Huntington Avenue, Boston. Massachusetts 02 115
rn A new passive sampler for ozone/oxidants and its simple analytical system have been developed. The sampler consists of a carbon paper collector coated with nylon-6 polymer and potassium iodide, several layers of membrane filters to remove interferences, and a spacer and Teflon meshes to control sampling rate. Iodine liberated by an oxidation reaction of KI with ozone is stabilized by forming a charge-transfer complex with nylon-6 and is accumulated in the nylon-6 layer. The amount of I2 is determined by constant-current coulometry using the collector as a positive electrode and a zinc plate as a counter electrode. This procedure is simple, requiring no pretreatment. The sampler was applicable for measurement of 6-8-h average personal exposures to ozone/oxidants. The effects of surface wind velocity, temperature, and humidity were small. However, with relative humidities below 20%, it would underestimate the ozone/oxidant concentration.
Introduction Atmospheric ozone has been a serious environmental problem in industrialized countries because of its adverse health effects. Peak ambient ozone concentrations are still high enough to cause transient changes in lung function, respiratory symptoms, and airway inflammation in healthy people (I). These transient effects were more closely related to cumulative daily exposure than the l - h peak concentration of ozone. The effect of long-term chronic exposures to ozone is not defined yet, but current levels are sufficient to cause premature aging of the lung. Even in a rural area of western Massachusetts, for example, hourly ozone concentration exceeded 100 ppb for more than 6 h a day, while nitric oxide and nitrogen dioxide concentrations were below 20 ppb (1). Personal exposure +Presentaddress: National Institute of Industrial Health, Ministry of Labor, 6-21-1 Nagao, Tama-ku, Kawasaki, Kanagawa 214 Japan. 744
Environ. Sci. Technol., Vol. 26, No. 4, 1992
levels to ozone, however, have not been clarified yet due to lack of a suitable personal sampler. Several types of analyzers for ozone in air are commercially available (2). One is the photometer, which measures ultraviolet absorption of ozone a t 250-260 nm. Another is the chemiluminescence detector, which measures light produced by a reaction between ozone and ethylene. The chemiluminescence method is specific to ozone and suitable for ambient air monitoring. An analyzer based on amperometry is also available. The neutral buffered potassium iodide (NBKI) method is a wet chemical method to measure ozone/oxidants in ambient air (3). In the NBKI method, ozone/oxidants in the air are introduced into the neutral buffered KI solution and liberate I,. The amount of I2 is determined by measuring the UV absorbance of the solution at 365 nm. A passive sampler for ozone using the reaction of ozone and 1,2-dipyridylethylene, and spectrophotometric determination, was reported ( 4 ) . The sampler is simple and specific to ozone, but is not applicable to personal monitoring, because it requires shielding from UV radiation and wind. An attempt to apply the NBKI method to the passive sampler using a filter paper impregnated with the NBKI solution was reported by Suzuki et al. (5) After the filter paper was exposed to air, I, on the filter paper was extracted and titrated with sodium thiosulfate. This passive sampler suffered a loss of I2due to sublimation of I2 during and after the sampling, with resultant low sensitivity. To apply the NBKI method to personal exposure measurements, the vapor pressure of I, must be lowered to prevent loss. The sublimation of I, observed with the NBKI filter paper method could be avoided by absorbing the I, on nylon-6, which is known to form a charge-transfer complex (CTC) with I2 (6). This interaction could lower the vapor pressure of 12. The liberation of I2followed by formation of the CTC can be regarded as a charge process of a pos-
0013-936X/92/0926-0744$03.00/0
0 1992 American Chemical Society
itive electrode of a ZnlZnI,II,-nylon-6 battery (7). Since the CTC is an active material of the positive electrode of the ZnlZnI,II,-nylon-6 battery, the amount of I, absorbed by nylon-6 can he simply determined by discharging the battery. In other words, the amount of ozone/oxidant exposure can he determined by discharging the battery. We have developed a passive ozone/oxidant sampler based upon this principle. The basic processes of the ozone/oxidant sampler are as follows: (1)Ozone/oxidants are transported from hulk air to the collector surface, made from a carbon fiber disk coated with nylon-6 and KI, by molecular diffusion; (2) a chemical reaction between ozone/oxidants and KI occurs at the surface of the KI layer where I, is liberated; (3) the liberated I, is absorbed by the nylon-6 layer hy forming a CTC. A galvanic cell was made using the exposed collector as a positive electrode and a zinc plate as a negative electrode. The CTC was electrochemically reduced by dischargingthe galvanic cell. Since the amount of CTC is proportional to the ozone/oxidant e x p u r e s , the exposures can be determined hy measuring the discharge time of the battery a t a constant current. Basic performances of the ozone/oxidant collector were reported previously (8). We have developed an ozone/ oxidant sampler with the collector and diffusion harrier in order to apply it to actual ozone/oxidant exposure measurements. Linear relationships were obtained hetween ozone/oxidant exposures and the discharge time. In addition to the linear relationship, the major advantage of this method is its very simple analytical procedure, since no treatment is required for the sample analysis.
Experimental Section Collector Preparation. A carbon fiber disk (Kureha KG-200, 3 cm in diameter) was washed with 2 N HCI, water, and methanol and dried under vacuum. Calcium chloride dihydrate (Aldrich) was dehydrated by heating at 200 OC under vacuum for 2 h. A saturated solution of calcium chloride was prepared by mixing 100 g of the dehydrated CaC1, with 200 mL of methanol. Eighty milligrams of nylon-6 (Aldrich) was dissolved in 8 mL of the CaCI,-saturated methanol solution and diluted with 5 mL of methanol. A 2OO-rL aliquot of the nylon-6 solution was applied to the carbon disk using a micropipet. The methanol was evaporated under vacuum until the CaC1, crystal became visible on the surface of the disk (approximately 2 h). The crystallized CaC1, was washed with water and then with methanol. After drying, the disk was coated with 150 pL of a mixed solution of 0.2 N KI 0.2 N potassium acetate (AcOK) + 0.07 N dibasic potassium phosphate in MeOH + H 2 0 (12,v/v). The disks coated with the mixed solution were dried under vacuum. The prepared collector was conditioned over a potassium carbonate saturated solution (at 43% RH) for 1 day to absorb water and stored in a sealed container. Test Sample. Test samples were used for determining the optimal operating conditions of the coulometry and for storage testa. These samples were prepared by impregnating the collectors with a dihenzoyl peroxide-ether solution in order to make many collectors having nearly identical discharge times. Iodine was liberated by the oxidation reaction of dihenzoyl peroxide instead of ozone. KMnO, Filter. A glass fiber filter impregnated with potassium permanganate (Aldrich) was used to remove sulfur dioxide interference. A glass fiber filter (Whatman GF/C, 47 mm) was impregnated with 250 r L of a 0.5% aqueous solution of KMnO, using a micropipet. The filter was dried under vacuum for 2 h. Sampler Assembly (Figure 1). A polystyrene case (Gelman Science, Petri dish No. 7232) was used as the
+
w
Tenm Membrane
K M " G~I-
nber ' T h n
s-
Flgu18 1. Sampler assembly.
-
; 114'
TeRm Tubng
Glass Chamber
Figure 2. Schematic diagram of exposure system (glass chamber).
sampler case. An opening of 31 mm in diameter was made on the cover. The conditioned collector was placed at the bottom of the case with several layers of filters on it as follows: a Teflon membrane filter (Millipore Mitex pore size 5 pm), a spacer, a coarse Teflon mesh (Spectra/Mesh loo0 pm), the glass fiber filter containing KMnO,, a Teflon membrane filter, a fine Teflon mesh (Spectra/Mesh Macro Filter 150 rm). The cover was taped to the body of the case. Exposure Experiment (Figure 2). An exposure chamber, a 4-L Pyrex flask (Aldrich), was placed in an incubator (Precision Model 815) to control temperature. Four samplers were mounted on a turntable rotated hy a stirrer motor in order to evenly expose them to a test gas at various temperature and relative humidity conditions. The wind velocity on the surface of the sampler was calculated to he 0.1 m/s. Test air containing known concentrations of ozone, NO,, NO, and/or SO, was fed to the exposure chamber at a flow rate of 2.8 L/min. The gases were generated with an ozone calibrator (Thermo Electron Instruments Model 49PS) and a Dynacalibrator (Metronics Inc. Model 340) for NO, and SO,. A certified standard nitric oxide in nitrogen (9 ppm) was diluted with air and mixed with the test air. A fraction of the test air was p d through a humidifier flask containing distilled water to control relative humidity. Concentrationsof ozone, NO,, NO, and/or SO2 in the exposure chamher effluent and humidity inside the chamber were continuously monitored with an ozone analyzer (Monitor Lab Inc. Model MlOE), a nitrogen oxides analyzer (Thermo Electron Instruments Model 14B/E), an SO, pulsed fluorescence analyzer (Thermo Electron Instruments Model 43), and a humidity sensor (Vaisala HMP 113A). The effects of temperature and humidity were examined using this system. The effect of temperature was examined at 50% RH. The effect of humidity was examined a t 25 Envlron. Scl. Technol., VoI. 26, No. 4. 1992 745
'Fb.w
T
I I
-m Flpure 3. Wind tunnel.
"C. Exposure periods were 2 h. Wind Tunnel (Figure 3). A wind tunnel exposure system was used to evaluate wind effects on sampler performances and examine NO, interference. The wind tunnel was made of two acrylic cylinders: an inner cylinder (21.9 cm i.d., 152 cm long) and an outer cylinder (29.5 cm i.d., 188 cm long). Test air was generated and monitored with the same instruments used for the glass chamber experiment. The test air introduced in the wind tunnel was circulated between the two cylinders with a fan to maintain the wind velocity at a specific level. Four samplers were placed parallel to the wind direction a t 5 cm from the center of the inner tube (see Figure 3). Wind speed a t the surface of the sampler was monitored by a hot wire anemometer ( K m Model 415). The temperature in the tunnel was not controlled and ranged from 25 to 28 "C. Humidity was controlled to be within 4&55%. The effects of the face velocity and NO, interference were examined using this system. To examine the face velocity effect, samplers were exposed to 200 ppb ozone a t the face velocity of 0.1, 0.3, or 1 m/s for 3-4 h. To examine the NO, interference, the samplers were exposed to NO, or a 1:l ozone-NO, mixture for 6 h. The face velocity was set at 0.3 m/s. Storage of Sampler. It is important to ensure that the storage of the collector after sampling does not degrade it, because it is not always possible to analyze samples immediately after sampling. The stability of the CTC during a storage period was tested using the test samples and exposed samples. The stability of the CTC was evaluated by a recovery efficiency, which was a ratio of the discharge time after storage to the initial discharge time. The presence of the KMn04 filter paper, volume of the storage container, and temperature were considered to be potential factors affecting the stability of the CTC during the storage. The collector was sealed in polystyrene culture dishes with aluminum foil as a light shield and stored under various combinations of potentially destabilizing factors, such as with/without the KMnO, filter, a storage container volume of 3 or 13 mL, and two storage temperatures. Coulometric Determination (Figure 4). A galvanic cell for the discharge was made of 200 mL of 0.1 N NH4C1 electrolyte, a positive electrode of the ozone/oxidant collector, and a counter electrode of a zinc plate (0.025 x 7 X 10 cm; Aldrich). A 400-mL beaker was used as a container for the cell. The ozone/oxidant collector was clamped with a pair of platinum-tipped forceps. The cell was covered with polystyrene foam to prevent evaporation of electrolyte solution. The electrode potential of the collector was monitored using a Ag/AgCI reference electrode (Aldrich 211,3085). The discharge current was kept constant at 100 pA with a galvanostat (Hokuto Denko Ltd., 748
II
I
Environ. Sci. Technol., VOI. 26, NO. 4. 1992
I I 0.1N I I KCI mmputer
Galvanic Cell
Flgure 4.
Schematic diagram of discharge measurement system.
Flgure 5.
Discharge CUNes.
Model HA501G). The discharge time was counted while the electrode potential was above -4.015 V vs the reference electrode as shown in Figure 5. A sequence of the discharge time measurement was automated by using a personal computer (PC) with a GPIB interface. When a sample identification code was entered into the PC, it became ready for the data acquisition. When the collector was immersed in the electrolyte, a microswitch, which triggered data acquisition, was pressed by an arm holding the forceps. The electrode potential and the elapsed time information were monitored by the PC every 1s until the electrode potential reached 4 . 1 5 V. After the discharge was completed, the electrode potential and discharge time data were saved in a disk file. In order to determine the optimal conditions for the discharge time measurement, the effects of dissolved oxygen in the electrolyte and the repeatability of the discharge were tested. The effects of dissolved oxygen in the electrolyte were tested by comparing the discharge time obtained from oxygen-free electrolyte and air-saturated electrolyte. The oxygen-free electrolyte was prepared by purging it with nitrogen gas and the air-saturated electrolyte was made by shaking the electrolyte vigorously. Results and Discussion Composition of the Collector. The carbon disk was coated with nylon-6, KI, KHzP04,and CH,COOK. The function of each component is as follows: KI is a reactant of ozone; nylon-6 acts as a trap of I, and an interface between KI and the carbon fiber disk; KH,PO, and AcOK are a buffer and a humectant. Without the nylon layer, carbon fiber could not be coated with KI, because of its hydrophobic nature. When the CTC was formed by exposing the collector to ozone, the color of the nylon layer turned to yellow, which was
I
14 .-
4
4501
350-
- 8 o)
250-
E
x
2 a
0.44
04
0
1
2
3 4 5 6 wader content(mg/electrode)
7
I
8
Figure 6. Water content and sampling rate. Collectors with different water contents were exposed to 190-274 ppb ozone for 1.5 h in the glass chamber without a diffusion barrier to ozone. Water content was controlled by addition of CaCI,. Temperature and humidity of the test gas were 25 O C and 46-48%, respectively. Each data point shows the average and the standard deviation of three determinations.
different from the color of I, in KI solution (dark brown). So the formation of the CTC was visually evident by its yellow color, although no spectrum was measured. As shown in Figure 6, when the collector was exposed to the test air at 50% RH, the ozone/oxidant sampling rate was dependent on the water content of the collector. For the collector not treated with any humectant, the water content was zero and the sampling rate was less than that of the collector coated with a humectant. This suggested that a certain amount of water was required for the ozone/oxidant and KI reaction. At first the water content of the collector was adjusted by adding CaCl,, since it is a well-known humectant and was used in the collector preparation. When the water content of the collector was more than 1.7 mg, the sampling rate of ozone/oxidants was independent of the water content. The reaction between ozone and KJ in neutral solution is considered as follows (9): O3 + 21- + H 2 0 I, + O2 + 20H(1)
-
This shows t,hat the reaction requires water, the stoichiometry of ozone and 1, is unity, and the pH of the solution will increase as the reaction proceeds. In an alkaline solution the stoichiometry becomes less than unity, due to partial hypoiodite and iodate formation (10).
+ - +
303 + I503 + I,
+ 20H-
302
502
IO3-
2(10);
+ H20
etc.
Therefore, constancy of pH at the surface of the collector for the entire sampling period is important to have consistent stoichiometry for the reaction. To maintain the surface pH constant as well as the water content of the collector, AcOK and KH2P04 (pH 6.4) were used as a humectant and a buffer. The relative humidities over the saturated solutions of AcOK and CaCl, were 20 and 32% at 20 O C (IO),indicating that AcOK acts as a humectant in wider range of humidity than CaCl,. The collector contained 1.7-2.0 mg of water when AcOK was used as a humectant. As shown in Figure 7, the sampling rate was consistent over exposures ranging from 400 to 1450 ppb-h. Coulometry. Figure 5 shows discharge curves of the collectors exposed to different amounts of ozone. For the collector having a short discharge time, the electrode potential decreased gradually from the beginning of the
,/'
- Y = 0.274X, R = 0.989. (?
4
,/"
:\
150
/
-
Y= 0,291 0.291 X 18.4, R = 0.991, (n=24)
./'
-501 0
400
800
1200 Exposure (ppb.hour)
4 1800
Figure 7. Calibration curve. Samplers were exposed to 30-300 ppb ozone for 6 h in the wind tunnel. Face velocity was 0.3 m/s. Temperature and humidity were 25-28 OC and 40-55%, respectively. Eat'- data point shows the average and the standard deviation of four deti:mlnations. Data at 1800 ppb-h were excluded from the regression.
discharge and then decreased quickly when its potential reached to -0 V vs the reference electrode. The rapid decrease of the electrode potential suggested that the residue of I2 or CTC in the collector was very small. The curve at -0 V did not have any shoulder, indicating that active materials for the discharge might be 12/CTConly. For the collector having a long discharge time, the electrode potential increased due to the higher concentration of I, on the surface of the collector. The discharge curve at -0 V was similar to that of the collector having the short discharge time. A blank collector, which was not exposed to ozone, had a discharge time less than 1 s. Dissolved oxygen in the electrolyte had no effect on the discharge time measurement. The average discharge times and standard deviations ( n = 5) of the test samples in the oxygen-freeand air-saturated electrolyte were 343.9 f 2.9 and 347.6 f 4.7 s, respectively. When nitrogen gas was introduced to the electrolyte, the discharge time decreased by 94.7 s for the oxygen-free electrolyte and by 98.4 s for the air-saturated electrolyte. This suggested that disturbance of the electrolyte might increase the dissolution of I, from the collector surface, so that the discharge time became shorter. To avoid excessive I2 loss by disturbance of the electrolyte, no gases were introduced into the electrolyte. In addition to this, the discharge cell was covered with a lid to prevent convectional flow due to evaporation of the electrolyte, and the discharging was started immediately after immersion of the collector into the electrolyte. The repeatability of the discharge measurement was good. The coefficient of variation was 4% among 28 test sample measurements. Response to Ozone Exposure. A linear relationship was obtained between the discharge time and the amount of ozone exposured up to 1450 ppb-h (Figure 7). At 1800 ppbeh exposure, a decrease of the response was observed. A forced regression and normal regression lines were drawn on the figure using 24 data points. The data at 1800 ppb-h were excluded from the calculation. The slopes of the forced and normal regression lines were 0.274 and 0.291 (s/ppb-h), respectively. The correlation coefficient was 0.989 for the forced regression and 0.991 for the normal one. The sampling rate (mL/s) was defined as sampled ozone (mol) sampling rate (mL/s) = concn (mol/mL) X time (s) Environ. Sci. Technol., Vol. 26, No. 4, 1992
747
Table I. Response of the Sampler Containing a KMnO, Filter"
1
3oo
exposure
NO2
+ 03 : Y= 0.363X, R=0.99
1
n=9)
1250-
so* NO 0,
100 70 180
5 6 4
0.4 0.2 190
34 35 4.8
1.0x 10-3 1.0 x 10-3 2.6 X 10-1
'Three ozone samplers with a KMn04 filter were exposed to the test gases containing 03,NO, or SOz,separately. Temperature was 25 "C. Humiditv was between 46 and 48%.
The sampled amount of ozone was derived by assuming 1:l stoichiometry of the ozone and I, as shown in eq 1: sampled amount (mol) = discharge time(s) X current (A)/F (C/mol) where F is the Faraday constant. By setting the current at 100 PA and Faraday constant a t 96400 C/mol, and converting the units of the denominator from mol s-l mL-l to ppb-h, the sampling rate a t 25 "C is calculated from discharge time (s) sampling rate (mL/s) = 7.06 (2) exposure (ppb-h) The sampling rates calculated from the slopes of the forced and normal regression lines were 1.93 and 2.05 mL/s, respectively. The forced regression line was selected as a calibration line to calculate ozone exposure from the discharge time, because the discharge times of the blanks were very close to zero. The discharge times at ozone exposures below 400 ppbsh were shorter than the expected time from the forced regression line. It may be due to decomposition of a certain amount of ozone on the surface of the filters used as the diffusion barrier. When the exposures were more than 400 ppb-h, differences of the two regression lines were less 10%. Interferences. When the collectors (with no diffusion barrier) were exposed to test gas containing NO, or SO,, positive or negative interferences for the ozone sampling were observed. To eliminate the negative interference by SO,, a glass fiber filter containing KMn0, was used. After the KMn0, filter was installed, SO, showed practically no interference, as shown in Table I. SO, seemed to be oxidized by KMn04 and retained in the glass fiber layer. NO was considered to have a postive interference because KMnO, might oxidize NO to NOz. But NO had no interferant effects. Although several attempts were made, no appropriate method to remove the NO, interference without affecting O3was found. In order to evaluate the interference of NO,, the samplers were exposed to 45 or 95 ppb NOz for 6 h. The sampling rate of NO,, assuming 1mol of NO, liberated 1 mol of I,, was 0.54 mL/s, as shown in Figure 8, where the ozone calibration line was also shown. The NO2 sampling rate of 0.54 mL/s was 28% of the 1.93 mL/s ozone sampling rate. If the response to NO, is an additive process for the ozone sampling, the sampling rate for a mixture of ozone and NO, gas is expected to be a weighted sum of each sampling rate: sampling rate (mL/s) = 1.93 + 0.54[N021/[031 = 1.93(1 + 0.28[N0,]/[03]) or by converting the sampling rate to the discharge time according to eq 2, the discharge time is calculated from discharge time (s) = 0.27 (s/ppb-h) X ([ozone] (ppb)+ 0.28 X [NO,] (ppb)) X time (h) (3) 748
Environ. Sci. Technol., Voi. 26, No. 4, 1992
z
F Q
200-
F 150-
B A=
loo-
NO2 : Y= 0.076X, R=0.951, (n=9) 1200
0
Exposure (ppb.hour)
Flgure 8. Interference of NO,. The samplers were exposed to NOp or 1:l mixture of NOp and ozone for 6 h. The face velocity was set at 0.3 m/s. Temperature and humidity were 25-28 "C and 40-55 % , respectively. Each data point shows the average and standard deviation of four determinations.
To confirm this assumption, the samplers were exposed to a mixture of 55 ppb NO, and 56 ppb ozone or 105 ppb NOz and 111ppb ozone for 6 h. In Figure 8, the discharge times of the samplers exposed to the ozone-NO, mixture were plotted against the ozone exposures. The averages and standard deviations of the discharge times were 122.2 f 9.1 for the 55 ppb exposures and 242 f 7.4 s for the 111 ppb exposures. The calculated discharge times, using eq 3, were 140 and 228 s for 55 and 111 ppb exposures, respectively. This good agreement supports the additive assumption. To simulate a typical environmental situation, the samplers were exposed to a mixture of 110 ppb ozone and 45 ppb NO,. The discharge time increased lo%, as expected from the NO, interference. There are two possible ways to deal with the NO, interference: subtract NO, interference by simultaneously measuring NO2 concentration or consider the ozone/oxidant concentrations measured by this method as total oxidant concentrations. Effect of Face Velocity. The sampling rates were consistent with the change of face velocity from 0.1 to 1 m/s, when the samplers were exposed to 200 ppb ozone in the wind tunnel for 3-4 h. Temperature and humidity were 25-28 "C and 40-55%, respectively. In our sampler configuration, the diffusion path length of ozone/oxidants from the surface of the sampler to the collector was 4.1 mm. Dependence on the wind velocity is small enough to apply this method to the ozone/oxidant monitoring. Effect of Humidity. The sampling rate had a very weak positive correlation with relative humidity over ranges from 25 to 72%, when the samplers were exposed to 350 ppb ozone in the glass chamber for 2 h at 25 "C. The wind velocity on the surface of the sampler was calculated to be 0.1 m/s. When the relative humidity was 15%, however, the sampling rate was smaller than results at the higher relative humidity. This corresponds to the fact that the saturated AcOK-water solution released water below 20% RH. The decrease of sampling rate at low humidity may be due to decreasing water content during sampling. When the samplers are applied in an area where the relative humidity is less than 20%, ozone/oxidant concentrations will be underestimated. Effect of Temperature. Dependence of the sampling rate on temperature in range of 15-40 "C was negligible, when the samplers were exposed to 350 ppb ozone in the glass chamber for 2 h at 50% RH. The wind velocity on the surface of the sampler was calculated to be 0.1 m/s. N
120
K+S+F K-S+F K-S+R
E.
K+S+R K-S-R
U
K+S-R
40-
" I
0
7
14 Storage Period (day)
21
2s
Flgure 9, Storage of test sample. The test samples were placed In polystyrene culture dishes, shielded from llght with aluminum foil, and stored. Storage conditions were combination of three factors: (1) with (K+) or without a KMnO, filter (K-), (2) storage container volume of 13 (S+) or 3 mL (S-), and (3) storage temperature, Le., room (R) or refrigerator (F). The stability of the CTC was evaluated by a recovery efficiency, which was a ratio of the average discharge tlme of three test samples after the storage to the Initial discharge time.
The sampling rate is a function of absolute temperature to the power of 0.5, when the concentration is expressed by a dimensionless unit such as ppb, because the sampling rate is proportional to a molecular diffusion coefficient and gas density, and their dependency on absolute temperature is to the power of 1.5 for the diffusion coefficient and the power of -1 for the gas density. The change of the sampling rate between 15 and 40 "C is calculated to be -5% of the sampling rate at 25 "C. Effect of Storage. Exposed samplers could be stored in a refrigerator for 30 days after the exposure. The exposed sampler stored in a refrigerator retained 90% of the initial amount of I2 The temperature was found to be the major factor for the stability of the CTC during storage, while the presence of a KMn0, filter made no difference in the recovery. These were examined using the test samples as shown in Figure 9. When the test samples were stored at 4 "C in the refrigerator for 28 days they retained -90% of the initial 12, while at room temperature the recovery decreased to less than 90% in 2 weeks of storage. The test sample stored in a large-volume dish showed larger loss of 12. The dependency of the recovery on the volume of the dish and the storage temperature suggested that the loss was due to the slow evaporation of 12. Since oxygen in the air was considered as a potential oxidizer for the KI solution, storage experiments for unexposed blank collectors (small amount of I2 was added to clarify positive or negative changes) were conducted as well. No change in the discharge time of the blank collector, which was stored in the sealed dish containing the KMnO, filter for 20 days in the refigerator, was observed. Average discharge times of the blanks before and after the storage were 16.3 f 5.3 and 13.4 f 6.2 s ( n = 3). This
indicated that oxygen in the air did not produce 1, on the collector.
Conclusions A new passive sampler for ozone/oxidants has been developed. The basic performances were examined by exposing them to the test air. The sampler showed a linear response to ozone exposure up to 1450 ppbsh. The minimum detectable exposure was -400 ppbsh. Changes in the response caused by temperature and humidity were negligible. The effect of face velocity was very small. The sampler showed no response to coexisting SO2 or NO. The interference of NO2was additive and the sampling rate of NOz was 28% that of ozone. The exposed samples could be stored in a refrigerator for 4 weeks. The sampler is small and lightweight to use, accurate and very easy to analyze, so that it will be a suitable method for large-scale personal exposure measurements and multilocation measurements. 10028-15-6; KI, 7681-11-0; 12, 7553-56-2; Registry No. 03, nylon-6, 25038-54-4.
Literature Cited (1) Lippmann, M. J A P C A 1989,39, 672-695. (2) Rice, R. G. In Analytical Aspects of Ozone, Treatment of Water and Wastewater;Rice, R. G., Bollyky, L. J., Lacy, W. J., Eds.; Lewis Publishers: Chelsea, MA, 1986; Chapter 22. (3) Saltzman, B. E.; Gilbert, N. Anal. Chem. 1959, 31, 1914-1920. (4) Monn, C.; Hangartner, M. J. Air Waste Manage. Assoc. 1990,40, 357-358. (5) Suzuki, S.; Horiuchi, N.; Yoshimori, M.; Sibayama, M. Taiki Osen Gakkaishi 1983,18, 544. (6) Hishinuma, M.; Yamamoto, T. J . Mater. Sci. Lett. 1984, 3, 799-801. ( 7 ) Yamamoto, T.; Hishinuma, T.; Sugimoto, H.; Yamamoto, A. J . Electroanal. Chem. 1985, 194, 197. (8) Hishinuma, M.; Yanagisawa, Y.; Yamamoto, T. Development of a passive monitor for ozone/oxidants. Proc.A P C A Annu. Meet. 82nd 1989, Abstr. 89-29.7. (9) Sullivan, D. E.; Hall, L. C.; D'Ambrosi, M.; Roth, J. A. In Analytical Aspects of Ozone, Treatment o f Water and Wastewater;Rice, R. G., Bollyky, L. J., Lacy, W. J., Eds.; Lewis Publishers: Chelsea, MA, 1986; Chapter 5. (10) CRC Handbook f o r Chemistry and Physics, Student Edition; Weast, R. C., Ed.; CRC Press, Boca Raton, FL, 1990; Section E-36.
Received for review June 4, 1991. Revised manuscript received November 19,1991. Accepted November 27,1991. Part of this paper was presented at the 5 t h International Conference on Indoor Air Quality and Climate, Toronto, Ontario, Canada, July 29-August 3, 1990. Research described i n this article was conducted partially under contract to the Health Effects Institute (HEI), a n organization jointly funded by the United States Environmental Protection Agency (EPA)(Assistance Agreement X-822059) and automotive manufacturers. The contents of this article do not necessarily reflect the views of the HEI, nor do they necessarily reflect the policies of EPA, or automotive manufacturers.
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