Environ. Sci. Technol. 1989,2 3 , 321-327
Diurnal Concentrations of Volatile Polycyclic Aromatic Hydrocarbons and Nitroarenes during a Photochemical Air Pollution Episode in Glendora, California Janet Arey,” Roger Atklnson, Barbara Zieilnska, and Patricia A. McElroy Statewide Air Pollution Research Center, University of California, Riverside, California 92521
The diurnal concentrations of eight abundant, volatile polycyclic aromatic hydrocarbons (PAH) were measured with 12-h sampling intervals over a 9-day period in August 1986 at Glendora, CA, during a photochemical air pollution episode. For a more limited number of samples, several less abundant PAH, 1- and 2-nitronaphthalene, and 3nitrobiphenyl were also measured. The consistent meteorology throughout the study period allowed the effect of atmospheric reactions on the ambient PAH concentrations to be evaluated. From the observed PAH concentrations and their known rate constants for reaction with the hydroxyl radical, an estimate of the average daytime 12-h ambient hydroxyl radical concentration of 2 X lo6 molecule cm-3 was obtained. Introduction The polycyclic aromatic hydrocarbons (PAH) containing two and three rings (including biphenyl) are present primarily in the gas phase at the ambient temperatures encountered in southern California. Diurnal variations in the ambient concentrations of these PAH may result from varying emission patterns, meteorological factors such as mixing heights, and removal by chemical reactions, which may vary in importance during different periods of the day. Kinetic studies have shown that the major atmospheric loss process for the majority of these volatile PAH is by daytime gas-phase reaction with the hydroxyl (OH) radical (1-3).
We have shown that in ambient atmospheres the nitro derivatives of the two-ring PAH may be significantly more abundant than the particle-associated nitrofluoranthenes and nitropyrenes ( 4 ) . Additionally, laboratory studies in conjunction with ambient measurements suggest that the majority of nitroarenes present in ambient air are formed from the gas-phase reactions of N205 and/or the OH radical in the presence of NO, (5-10). Since the OHradical-initiated reaction is a daytime process and N2O5 reactions occur only at night [N205being in equilibrium with NO3radicals and NO2,with the NO3 radical photo, formation pathways are expected lyzing rapidly (I l ) ]these to be reflected in the diurnal variations observed for the volatile nitroarenes. We report here on the ambient concentrations of eight abundant, volatile PAH measured with 12-h day and night sampling intervals over a 9-day period during August 1986 at Glendora, CA, a site in the Los Angeles air basin approximately 20 km northeast, and generally downwind, of downtown Los Angeles. For a more limited number of sampling intervals, several less abundant PAH, 1- and 2-nitronaphthalene, and 3-nitrobiphenyl were also measured. The consistency of the meteorology throughout the 9-day study period allowed the effect of atmospheric reactions on the observed ambient concentrations of the volatile PAH to be evaluated. Experimental Section Sampling was conducted as part of the California Air Resources Board funded “Carbonaceous Species Methods 0013-936X/89/0923-0321$01 S O / O
Comparison Study” in Glendora, CA, in the summer of 1986. The 0800 PDT, August 12 to 0800 PDT, August 21 sampling period was characterized by moderately high photochemical air pollution. The lowest daily maximum for the ozone mixing ratio was 185 parts-per-billion (ppb) on August 13. On the other study days the ozone mixing ratio maxima ranged from 240 to 300 ppb (12). NO, mixing ratios were generally in the range of 50-200 ppb throughout the study period, and NO3 radicals were observed by differential optical absorption spectroscopy (DOAS) on the evening of August 13 and may have been present on the evenings of August 14, 19, and 20 (12). Tenax-GC cartridges were used to sample the volatile PAH and polyurethane foam (PUF) plugs to sample the nitroarenes, which are generally more than an order of magnitude less abundant than the parent PAH ( 4 ) . The PUF plugs were located in modified high-volume (Hi-vol) samplers downstream of a Teflon-impregnated glass fiber (TIGF) filter and thus collected both gas-phase PAH and nitroarenes as well as particle-associated species which were “blown-off’the particles during the collection period. Tenax-GC Cartridges. Sampling and Analysis. Two sizes of Tenax-GC cartridge were used for ambient air sampling. Precleaned (13) Tenax-GC (60/80 mesh) was used in “low-flow” cartridges (10 cm X 4 mm i.d. Pyrex tubes packed with 0.1 g of the solid adsorbent) and “high-flow” cartridges (10 cm X 1 cm i.d. Pyrex tubes packed with 0.6 g of the solid adsorbent), which were operated at -1 and -10 L min-’, respectively. Each lowflow cartridge had a backup cartridge in series to measure any breakthrough from the first cartridge. After the 12-h sampling periods, which yielded samples collected from -0.6 and -6 m3 of air for the low- and high-flow cartridges, respectively, the cartridges were placed in sealed test tubes and kept cool until analyzed, as follows. Deuteriated internal standards were added to the low- and high-flow Tenax-GC cartridges, respectively, in the following amounts (in micrograms): naphthalene-& (1.8, 16), biphenyl-d,, (0.7, LO), phenanthrene-dl, (0.6,0.6). The low- and high-flow cartridges were then eluted with 2 and 10 mL, respectively, of diethyl ether, which was subsequently solvent-exchangedto -0.2 mL of acetonitrile (using a microSnyder apparatus for the high-flow eluent). PAW were identified and quantified by combined gas chromatography/ mass spectrometry (GC/MS) with multiple ion detection (MID) using a Hewlett-Packard 5890 GC with a 7673A automatic sampler and interfaced to a 5970 Mass Selective Detector (MSD). A 30-m DB-5 capillary column (J&W Scientific, Inc.) was used, with injections made in the splitless mode. Calibration curves for the GC/MS/MID quantifications of the PAH were made for the molecular ion peaks of the PAH using the corresponding deuteriated species (or the deuteriated species most closely matched in volatility) as an internal standard. The National Bureau of Standards Standard Reference Material 1647 (certified PAH), with the addition of biphenyl, 1-and 2-methylnaphthalene, and the deuteriated internal standards, was utilized to make the calibration solutions.
0 1989 American Chemical Society
Environ. Sci. Technol., Vol. 23, No. 3, 1989 321
Polyurethane Foam Plugs. Sampling and Analysis. Two modified Hi-vol samplers with four PUF plugs (each -9 cm diameter X 5 cm thickness; cleaned by Soxhlet extraction for -16 h in CH2C12,followed by -16 h in methanol) located in series beneath a TIGF filter were operated at -23 standard ft3 min-' for 12-h intervals, yielding samples collected from -470 m3 of ambient air per sampler. After sampling, the PUF plugs were individually wrapped in aluminum €oil and cooled. Prior to analysis, the PUF plugs were combined into six samples consisting of a single day sample and a single nighttime sample from the early portion of the study, a single day sample and a single nighttime sample from the latter part of the study, and two composite samples consisting of four daytime collections and four nighttime collections, as follows: August 13, 0800-2000 PDT; August 13-14, 2000-0800 PDT; August 15,16,17, and 18,0800-2000 PDT; August 15-16,16-17,17-18,18-19, 2000-0800 PDT; August 20, 0800-2000 PDT; and August 20-21, 2000-0800 PDT. The samples from the single 12-h day or night collections each consisted of eight PUF plugs (four from each Hi-vol) which were extracted together. The first three PUF plugs from each collection in the composite samples were combined for extraction, with the fourth PUF plugs being combined and analyzed as two separate samples (day composite and night composite) to check for breakthrough during collection. After being spiked with deuteriated internal standards including l-nitronaphthalene-d,, phenanthrene-&,, anthracene-dlo, fluoranthene-dlo, pyrene-dlo, and dibenzothiophene-d8 in amounts approximately proportional to the ambient volume sampled, the PUF plugs were Soxhlet extracted overnight with CH2C12 The extracts were concentrated by rotary evaporation under vacuum to N 1mL, filtered through 0.45-pm Acrodiscs (Gelman Scientific), and further concentrated under a stream of nitrogen to -200 pL. The PUF plug extracts were then fractionated by high-performance liquid chromatography (HPLC) with an Altex semipreparative scale Ultrasphere Silica column (1 cm X 25 cm). The HPLC system consisted of a SpectraPhysics Model 8100 chromatograph, Model 4100 computing integrator, Model 8400 UV/visible detector and an ISCO fraction collector. The mobile-phase program employed, at a flow rate of 3 mL min-', was as follow's: 100% n-hexane for 5 min, then a linear gradient to 95%/5% n-hexane/CHzCl2over 5 min, followed by a linear gradient to 100% CHeC12over 25 min, held at 100% CHzClzfor 10 min, linear gradient programming to 100% CH3CN over 10 min, and held isocratic for an additional 10 min. A fraction containing the PAH (and the sulfur heterocycle dibenzothiophene) was collected from 4 min to 22 rnin and a nitroarene-containing fraction from 22 min to 34 min. These fractions were concentrated by rotary evaporation and then taken just to dryness under a stream of nitrogen. After dissolution in CH3CN or CH2C12,these HPLC fractions were analyzed by GC/MS/MID with the MSD system described above. The PAH present in the PUF plug extracts were identified and quantified as described above for the Tenax samples. For analysis of the nitroarenes, the molecular ions and several characteristic fragment ions were monitored, as follows: nitronaphthalenes ( m / z 173,145,143,127,126,115),l-nitronaphthalene-d7 ( m / z 180, 152, 134, 1221, methylnitronaphthalenes (m/z 187,157,141,140,115), nitrobiphenyls and nitroacenaphthenes ( m / z 199, 153, 152, 151, 141), nitrofluorene ( m / z 211, 165, 164), and nitroanthracenes and nitrophenanthrenes (m/z 223,193,177,176,165). 1322
Environ. Sci. Technol., Vol. 23, No. 3, 1989
and 2-Nitronaphthalene and 3-nitrobiphenyl were quantified on the basis of their molecular ion peaks by using calibration curves with l-nitronaphthalene-d7 as the internal standard. Chemicals. All solvents were glass distilled (Burdick & Jackson). The diethyl ether was passed through a column of activated alumina prior to use to remove possible peroxide contaminants. The deuteriated chemicals used as internal standards were as follows: biphenyl-d,,, phenanthrene-d,,, anthracene-dIo, and pyrene-dlo (Cambridge Isotope Laboratories); fluoranthene-dlo and dibenzothiophene-d8 (MSD Isotopes Inc.); and naphthalene-d8and l-nitronaphthalene-d, (Aldrich Chemical Co.). Standard chemicals used for retention time and fragment ion abundance matches were as follows: naphthalene, acenaphthylene, acenaphthene, biphenyl, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, 1- and 2nitronaphthalene, 2-, 3-, and 4-nitrobiphenyl, 2-nitrofluorene, and 9-nitroanthracene (Aldrich Chemical Co.); 1- and 2-methylnaphthalene, (Chem Services); and Standard Reference Material 1647, certified PAH (National Bureau of Standards). Acephenanthrylene was synthesized as described elsewhere (9). 3- and 5-Nitroacenaphthene were synthesized by nitration of acenaphthene with N204,by using the procedure described by Pitts et al. (14).
Results
PAH Measured on Tenax-GCCartridges. The most abundant PAH collected on the Tenax-GC cartridges were naphthalene and 1- and 2-methylnaphthalene, with the highest 12-h average naphthalene concentration measured during this study being 6.1 pg m-3 (1.1ppb). The observed 12-h average ambient concentrations of naphthalene, 1and 2-methylnaphthalene, acenaphthylene, biphenyl, acenaphthene, fluorene, and phenanthrene are given in Table I. The naphthalene concentrations given in Table I have been calculated by using the low-flow Tenax cartridge data, while the remaining PAH concentrations were calculated from the high-flow Tenax data. Less than 7% (and generally < 2 % ) of the naphthalene observed on the first low-flow cartridge was observed on the backup cartridge, showing that naphthalene was collected quantitatively on the low-flow cartridges. The naphthalene concentrations calculated from the amounts on the high-flow cartridges were consistehtly lower than those calculated from the low-flow cartridges, indicating breakthrough of naphthalene at the higher sampling rate. In contrast, there were no evidence for breakthrough of methylnaphthalenes when sampled on the high-flow cartridges, and the remaining less volatile PAH for which data are Liven in Table I are also expected to have been quantitatively collected. The single exception may be acenaphthylene, for which degradation during sampling has been reported (13). The volatile PAH measured on the Tenax cartridges were generally more abundant during the nighttime than daytime sampling intervals. Figure 1shows the measured ambient concentrations of naphthalene and the methylnaphthalenes during this study period. The concentration profiles of the methylnaphthalenes were remarkably similar, with 2-methylnaphthalene always being more abundant than l-methylnaphthalene. PAH and Nitroarenes Measured on PUF Plugs. Phenanthrene and fluorene were the most abundant PAH observed in the PAH-containing HPLC fraction of the PUF plug extracts, and the nitronaphthalenes were the most abundant nitroarenes in the more polar HPLC
Table I. Concentrations (ng n ~ -of ~ )Volatile PAH Sampled onto Tenax-GC Solid Adsorbent at Glendora, CA, in August 1986 (Day, 0800-2000 PDT; Night, 2000-0800 PDT)
date 8/12/86 day 8112-13/86 night 8/13/86 day 8113-14/86 night 8/14/86 day 8114-15186 night 8/15/86 day 8115-16186 night 8/16/86 day 8116-17/86 night 8/17/86 day 8117-18/86 night 8/18/86 day 8/18-19/86 night 8/19/86 day 8119-20/86 night 8/20/86 day 8/20-21/86 night av daytime av nighttime a
Sampled at
6,000
-
concn, ng m-S 1-methyl2-methylbinaphthalenea naphthaleneb naphthaleneb acenaphthyleneb phenylb acenaphthaleneb fluoreneb phenanthreneb d d d d d 25OC 150' 2200 64 49 32 220 39 900 500 5000 26 4 30 -3 95 320 160 2400 51 22 37 170 12 730 390 4800 20 4 30 70 -3 260 130 2500 40 34 17 100 23 640 330 3000 d d d d d 19oc 180' 2800 42 21 35 10 66 730 380 4100 16 -44 23 -3 52 200 98 3200 37 24 40 98 -3 700 350 3400 20 27 -5 36 -3 170 76 2000 51 47 30 4 54 680 330 4300 26 31 5 -3 43 260 4100 120 46 28 43 -3 67 570 4200 280 21 23 4 -3 36 200 90 4300 50 44 28 60 -3 600 290 3800 29 33 6 -3 53 320 4100 150 d d d d d a6oc 490' 6100 3100 4300
1 L min-'.
1
04 12
O!
12
130 370
Sampled at
-
240 710
3 12
14
13
14
5 25
10 L min-', except as indicated. Value from low-flow Tenax.
i
NAPHTHALENE
13
55 100
I
15
16
17
18
19
20
21
15
16
17
18
19
20
21
August 1986 Figure 1. Ambient concentrations of naphthalene (A,A),l-methyinaphthalene (0, B), and 2-methylnaphthalene (0, a) measured for 12-h daytime (0800-2000 PDT; open symbols) and nighttime (2000-0800 PDT; solid symbols) sampling intervals in Giendora, CA, from 0800 PDT, August 12, 1986, to 0800 PDT, August 21, 1986.
fraction. The measured ambient concentrations of fluorene, phenanthrene, anthracene, dibenzothiophene, fluoranthene, pyrene, acephenanthrylene, 1- and 2-nitronaphthalene, and 3-nitrobiphenyl for the six PUF plug samples are given in Table 11. While the PAH more volatile than fluorene were also present in the PUF plug extracts, breakthrough resulted in the measured concentrations being only a small fraction of the true ambient concentrations (4). From the composite samples in which the fourth PUF plugs were extracted separately (the amounts on the fourth PUF plugs are listed in parentheses in Table 11),it is obvious that fluorene was not collected
28 44
23 48
No high-flow Tenax sample.
quantitatively under our sampling conditions and that some breakthrough of phenanthrene and the nitronaphthalenes also occurred, particularly during the daytime collection periods. Quantitative collection of fluorene on the PUF plugs was not expected (15),and breakthrough of phenanthrene is also consistent with its calculated breakthrough volumes for sampling temperatures of 31-38 "C (the maximum afternoon temperatures attained during this study) (15). We observed
