Environ. Sci. Technol. lW2, 26, 2251-2262
Rapaport, R. A.; Eisenreich, S. J. Environ. Sci. Technol. 1984,18, 163-170. Isnard, P.; Lambert, S. Chemosphere 1989,18,1837-1853. Baker, J . E.; Capel, P. D.; Eisenreich, S. J . Environ. Sci. Technol. 1986,20, 1136-1143. New, A. L.; Pingree, R. D. Deep Sea Res. 1990, 37, 1783-1809.
(79) Pingree, R. D.; LeCann, B. J. Mar. Biol. Assoc. U.K. 1990, 70, 857-885.
Received for review May 5, 1992. Accepted July 9, 1992. Financial support from the Excma. Diputacion Fora1 de Guipuzcoa is acknowledged.
PM-10 High-Volume Collection and Quantitation of Semi- and Nonvolatile Phenols, Methoxylated Phenols, Alkanes, and Polycyclic Aromatic Hydrocarbons from Winter Urban Air and Their Relationship to Wood Smoke Emissions Steven
B. Hawthorne,* David J. Miller, John J. Langenfeld, and Mark S. Krlegsrt
University of
North
Dakota, Energy and Environmental Research Center, Campus Box 8213, Grand Forks,
Organic pollutants from winter urban air were collected using a conventional PM-10 high-volume air sampler (68 m3/h) which had been modified to include polyurethane foam (PUF) sorbent sheets behind the quartz fiber fdter. Fifty-five major semivolatile and nonvolatile pollutants including C14-C26 alkanes, PAHs ranging from acenaphthylene (M= 152) to those with M = 252, phenols, and methoxylated phenok were efficiently collected on the filter and PUF sorbent sheets and were quantitated in the unfractionated extracts using GC/MS. In 22 samples collected at six different locations in Minneapolis, MN, and Salt Lake City, UT, the average weight percent contributions of each compound class measured were a~ follows: n-alkanes, 23%; PAHs 11%; methoxyphenols, 21%; and phenols, 45%. Methoxylated phenol concentrations were highest in,residential areas with high wood burning, alkanes were highest in high traffic areas, and phenols and PAHs were associated with all types of sampling locations. Guaiacol (2-methoxyphenol) and its major derivatives showed excellent correlations (r2 ca. 0.74-0.90) with the fraction of “new“ (wood smoke-derived) PM-10 carbon determined by 14C analysis, demonstrating that their measurement could be used to determine the fraction of PM-10 particulate carbon contributed by residential wood burning. Introduction Residential wood burning is a major source (up to 80%) of inhalable particulate carbon and associated mutagenic polycyclic organic compounds in winter urban air (1-7). Additionally, wood smoke from fireplaces and wood stoves contains high concentrations of phenol, cresols, and semivolatile and nonvolatile methoxylated phenols including guaiacol (2-methoxyphenol) and its derivatives from softwood burning and both guaiacol and syringol (2,6-dimethoxyphenol) derivatives from hardwood burning (8,9). Since total concentrations of wood smoke phenols and methoxylated phenols emitted from residential chimneys wood average ca. 200-350 pg/mg of particulate carbon (9), burning is expected to be a major source of atmospheric phenolics in the winter air of northern cities. Unfortunately, the measurement of semivolatile and nonvolatile (i.e., particulate ansociated) organic air pollutants in urban air has largely focused on the major organics found in vehicle exhaust, Le., polycyclic aromatic hydrocarbons (PAHs) and alkanes, with much less emphasis placed on Present address: Department of Chemistry, Indiana University, Bloomington, IN.
North
Dakota
58202
more polar organics (10-18). Phenols are known to be present in high concentrations in urban rainwater and ambient air (1!&22), but there have been no reports describing the concentrations of methoxylated phenols in urban air, despite their high emission rates from residential wood burning (9). Recently, the potential importance of methoxylated phenols for accelerating the photochemical degradation of PAHs in urban air has also been reported (23). The f i t purpose of this study was to determine whether phenols and methoxylated phenols attain significant concentrations in winter urban air impacted by residential wood burning and to compare the concentrations of these species with semi- and nonvolatile organics more commonly measured in urban air, i.e., PAHs and alkanes. Since wood smoke is known to be a major contributor to PM-10 inhalable particulate matter &e., particles with an aerodynamic diameter of < l o pm), a second goal was to investigate the use of methoxylated phenols as wood smoke-specific tracers for source apportionment of inhalable particulate (PM-10) carbon. So that the results of these investigations would best relate to regulatory considerations, sample collections were performed using a conventional PM-10 high-volume air sampler. However, since the majority of phenols and methoxylated phenols reported to be emitted from wood stoves and fireplaces are semivolatiles, a simple modification of the sampler was performed to allow quantitative collection of the semivolatile phenolics onto polyurethane foam (PUF) sorbent sheets under air flow conditions (Le., 68 m3/h or 40 ft3/ min) that maintain the 10-pm sampling cutoff. Three sampling sites were chosen in and around each of two cities to include highly residential areas with little vehicle traffic, residential areas surrounded by heavy vehicle traffic, and nonresidential (i.e., downtown business) areas. The 55 individual phenols, methoxylated phenols, n-alkanes, and PAHs which had the highest concentrations were quantitated in each sample. Finally, the correlations between the concentrations of methoxylated phenols (proposed as specific tracers of wood smoke pollution) and the fraction of “new” (Le., wood smoke-derived) inhalable particulate carbon were determined based on 14Canalysis of the fdter samples (3, 24, 25). Experimental Section Sample Sites. Samples were collected between November 1988 and February 1989. Minneapolis, MN, and Salt Lake City, UT, were chosen as cities where the wood fuel source is primarily hardwoods and softwoods, re-
0013-938X/92/0926-2251$03.00/0 0 1992 American Chemical Society
Environ. Sci. Technol., Vol. 26, No. 11, 1992 2251
1
Flgwe 1. Modification of the PM-10 hlgh-volume filter head to accept the PUF sorbent sheets. The fllter holder was extended by 10.2 cm (4 in.) by welding an extenslon of stainless steel sheeting between the filter support screen and the beginnlng of the tapered portion of the head. An additlonal stainless steel screen was added at the bottom of the extension to support the two 18-cm X 23-cm X 5-cm (7-In. X 9-in. X 2-in.) PUF sorbent sheets.
spectively. All sampling locations were located on private land and were secured with permission of the owner. The three Minneapolis sites were located in an outlying suburb with no heavy traffic, a downtown residential area with several nearby highways, and a nonresidential downtown location. Similar locations were found in Salt Lake City, except that a nearby ski resort (Park City) was used for the low vehicle traffic residential site. The sampler was placed a t ground level at all sites. Sample Collection Using a High-Volume PM-10 Particulate Sampler Modified for P U F Sheets. Polyurethane foam (PUF) was chosen as the sorbent for this study, because it has been wed to quantitatively collect phenols and methoxylated phenols found in wood smoke from residential chimneys (9),and because it allows high sampling flow rates. PUF (polyether type, grade no. 3014) was obtained as 18-cm x 23-cm X 5-cm (7-in. X 9-in. X 2-in.) sheets from Olympic Products (Greensborough, NC) and cleaned by sonicating for 4 h with four changes of acetone. Between solvent changes, the PUF sheets were compressed to remove as much acetone as possible to avoid carryover of extracted background components (primarily the antioxidant, butylated hydroxytoluene). After extraction, the PUF sheets were dried under clean air and stored in the dark in 1-L glass bottles with Teflon-lined lids. All samples were collected using a General Metal Works high-volume air sampler equipped with a Model G1200 PM-10 sampling head and a Model G3000 filter holder for 20-cm X 25-cm (18-cm x 23-cm unmasked area) quartz fiber filters (Whatman QM-A). The filter holder was modified as shown in Figure 1so that two 18-cm X 23-cm X 5-cm PUF sheets (“front” and “back”, ca. 50 g each) could be placed directly under the quartz fiber filter. [A similar approach for high-volume air sampling with PUF sorbent sheeta has recently been reported by Hart et al. (26)].Each sample was collected for 12 h at the standard 68 m3/h (40 ft3/min) flow rate required to maintain the 10-pm particle size cutoff of the sampling head. No conscious attempt was made to sample during particular weather patterns, and (unless otherwise noted) samples were collected beginning either at 7 a.m. or at noon. After collection, the filter and each PUF were placed in separate 0.5- or 1.0-L glass jars (respectively)with Teflon-lined lids and stored in the dark at 4 “C until analyzed. Sample blanks were collected a t each site by assembling the air sample in a normal manner (including loading the filter and PUF sheets), then removing the filter and PUF sheets, and storing them in a manner identical to that used for the normal samples. 2252 Envlron. Scl. Technol., Vol. 26, No. 11, 1992
Sample Extraction. One-quarter of each filter was divided to perform duplicate analyses of the particulate carbon content. The second quarter of the filter was submitted to the University of Arizona Accelerator Mass Spectrometry Facility (Tucson, AZ) to determine the fraction of new carbon using 14Canalysis (3,24,25). The quantitation of the individual semi- and nonvolatile organics was based on duplicate extractions and analyses using two quarter sections each of the filter and PUF sorbents. Each PUF quarter was extracted for 6 h by sonication with 230 mL of acetone in a 250-mL jar. Isotopically labeled internal standards including guaiacol-d4 (10.4 pg, synthesized as described in ref 271, pyrene-dlo (10.0 pg, purchased from MSD Isotopes, St. Louis, MO), and eicosane-d42(10.0 pg, purchased from MSD Isotopes) were added as internal standards prior to sonication. The acetone extracts were concentrated under a gentle stream of clean nitrogen to ca. 1 mL for GC/MS analysis. Duplicate quarter sections of the filters were extracted in an identical manner, except that only 100 mL of acetone was used for each section. The extraction efficiencies obtained using this approach were investigated by performing spike recoveries [for the all of the phenols and methoxylated phenols available as standard compounds ( 9 ) ] and by multiple extractions of PUF (with acetone) and filter sections (with both acetone and methylene chloride) which had been used to collect air samples. All of the test spiked compounds showed >95% recovery, and all of the alkanes, PAHs, phenols, and methoxylated phenols were recovered (>90%) in the first extract (versus the quantities of each species in the second extract). GC/MS Analyses. All GC/MS analyses were performed using a Hewlett-Packard Model 5985 GC/MS in the electron impact (EI) mode with a scan range of 50-300 amu. Injections (1pL) were performed at a split ratio of ca. 1:30 into a 20-m DB-5 (250-pm i.d., 0.1 pm film thickness) column supplied by J&W Scientific (Rancho Cordova, CA). The GC oven temperature program was 80 “C (held for 2 min) followed by a temperature ramp at 8 OC/min to 330 “C. All species were identified on the basis of comparisons of their mass spectra and retention indexes with that of authentic standards except that 2,4-dimethylphenol was used for the only C2 phenol standard. Additionally, authentic standards were used for all of the derivatives of guaiacol except the propyl and acetonyl derivatives, and all of the derivatives of syringol except the methyl, ethyl, propyl, and acetyl derivatives (8). Quantitations were based on five-point standard curves generated using authentic standards for each individual species, except that estimated relative response factors (compared to guaiacol) reported earlier (9) were used to quantitate the methoxylated phenols for which authentic standards were not available. Each species was quantitated on the basis of the integrated area of its molecular ion (compared to that of the appropriate internal standard) except for the n-alkanes, which were quantitated on the basis of the ion at m/z = 71. Quantitations for PAHs (and oxygenated PAHs), alkanes, and phenols and methoxylated phenols were based on the areas compared to the internal standards pyrene-d,, (integrated at mJz = 212), eicosane-d,, (integrated at m/z = 82), and guaiacol-d4 (integrated at m/z = 128), respectively. All of the concentration values discussed below are based on the average of the duplicate extractions and analyses from each filter and PUF sorbent sheet. Results and Discussion (I) Sample Collection a n d Analysis. Sample Analysis. The GC/MS analysis of a typical urban air
sample collected from a residential neighborhood impacted by both wood smoke and vehicle exhaust is shown in Figure 2a and b. As would be expected for the unfractionated filter and PUF extra&, the chromatograms are very complex and contain a large number of poorly resolved species as shown by the reconstructed total ion current chromatograms (TIC). However, when the selected ion plots are generated from the same GC/MS runs for the masses used to quantitate the individual species, each of the organics quantitated in this study shows a well-resolved peak, and in most cases, the species of interest shows the most intense peak in its selected ion chromatogram. All filter blanks showed virtually no detectable species, and none of the phenols, methoxylated phenols, PAHs, and alkanes that were the focus of this study were detected in either the filter or PUF blanks. The PUF blanks did contain one major artifact (the large peak at ca. 12.5 min in the TIC chromatogram shown in Figure 2a; however, this species (tentatively identified by its mass spectrum as a branched isomer of octanoic acid) did not interfere with the quantitation of the individual organics that were the focus of this study, as shown by the selection ion plots in parta a and b of Figure 2. For each of the filter and PUF samples, the agreement between the duplicate extractions and analyses were good (generally 2:1, chromatographic retention would indicate that the front and back sheets combined contain >85% of the total analyte (26). All species reported in this study displayed >70% retention on the front PUF sheet and were therefore considered to be quantitatively retained on the two PUF sheets. The proportions of the individual semivolatiles found in the sorbent sheets versus on the particulate filter generally followed volatility considerations. For example, all of the phenols (phenol to C2 phenols, boiling points 108 "C to ca. 120 "C) were found only in the PUF sorbents, as were all of the guaiacol derivatives except for the least volatile guaiacol derivatives, 4-formylguaiacol (vanillii; bp = 280 "C) and 4-acetylguaiacol. In a similar manner, syringol (bp = 261 "C) was found mostly in the PUF, while the less volatile derivatives (e.g., formylsyringol or "syringaldehyde") were found only on the filter. The nalkanes C14 (bp = 253 "C) to C16 (bp = 287 "C) were only found in the PUF sorbents, while the average proportion of the higher molecular weight alkanes found on the PUF was ca. 92% for C17 and dropped to ca. 7% for C25. All of the PAHs more volatile than phenanthrene were found only in the PUF; phenanthrene and anthracene averaged 92%, and fluoranthene and pyrene averaged ca. 50% in the PUF as compared to the filter. Higher molecular weight PAHs were found only on the filters. It should be noted, however, that these samples were collected in the winter, and both the retention on the filter and retention on the PUF would be expected to be lower during sampling of summer air. It should also be noted that the proportions of each analyte found in the filter and PUF extracts do not necessarily represent the vapor/particle distribution which existed in the ambient air since both adsorption to and volatilization from the filter can occur during sampling of the semivolatiles (28, 29). (11) Organics in Winter Urban Air. Ambient Air Concentrations of Phenols, Methoxylated Phenols, PAHs, and Alkanes. Preliminary analyses of the PUF and filter extracts showed that the major species collected in all of the winter air samples were phenols, methoxylated phenols, alkanes, and PAHs. Two additional oxygenated PAHs, 9-fluorenone and dibenzofuran, were also present in significant concentrations. The total concentrations of the species in each major compound class are summarized in Table I, concentrations of the major individual methoxylated phenols are shown in Table 11,concentrations of the major phenols and oxy-PAHs are shown in Table 111, and the average distribution of each n-alkane and PAH is summarized in Table IV. In addition to the species listed in Tables I-IV, several lower molecular weight aromatics including alkylbenzene, alkylindan, alkyltetralin, and dkylnaphthalene isomers were identified in the PUF extracts; however, the concentrations of these species are not reported here since they were not quantitatively collected on the PUF sorbent sheets as discussed above. The concentrations of the alkanes and individual PAHs shown in Tables I and IV agree reasonably well with those Envlron. Scl. Technol., Vol. 26, No. 11, 1992 2253
1
I
n-alkanes
c1s
mlz = 7 1
178
PAH s
r-194
4-methyl
cpo
202
228
252
i
154
738
198
r4-allylgualacol
164 1 1-4-propenylguaIacoI
4-acetylsyrlngol I
I
I
,~
a-propylgualacol
, , , d< , , 10
.,
,
acetonylsyrI",r,
,
,
,
,
,
,
i;'acety~gualaco~
, hL$*
,
, , , , ,
20
Retenllon llme (mlnl
,
L
, , 30
10
20
30 Retentlon Time (rnln)
40
Figure 2. W / M S separatlon of the unfractlonated extracts of the PUF sorbent sheet (a, left) and the particulate fllter (b, right) from a typical hlgh-volume air sample collected in a resldentiil neighborhood impacted by both wood burning and vehicle exhaust. The numbers above the peaks indicate the mass used to generate the reconstructed ion plots. Chromatographic condklons are given in the text.
2254
Environ. Scl. Technol., Vol. 26, No. 11, 1992
Table I. Concentrations of Major Compound Classes i n Winter Urban Air concentration ( n ~ / r n ~ ) ~ alkanes (C14-C26) syringols guaiacols
location”
day
mg of c(
