Environ. Sci. Technol. 1997, 31, 3593-3599
Spatial and Temporal Variation of Polycyclic Aromatic Hydrocarbons in the Arctic Atmosphere C . J . H A L S A L L , * ,† L . A . B A R R I E , † P. FELLIN,‡ D. C. G. MUIR,§ B. N. BILLECK,§ L. LOCKHART,§ F. YA. ROVINSKY,| E. YA. KONONOV,| AND B. PASTUKHOV| Atmospheric Environment Service, 4905 Dufferin Street, Downsview, Ontario M3H 5T4, Canada, Bovar Environmental, 2 Tippett Road, Toronto, Ontario M3H 2V2, Canada, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada, and Institute of Global Climate and Ecology, 20-b Glebovskaya Street, 107258 Moscow, Russia
In the first multi-year arctic air sampling program, PAHs were sampled (vapor and particulate) every week at three locations in the Canadian and Russian Arctic. Data are presented here for the years 1992-1994. The geometric mean ∑PAH concentrations (where ∑ ) 16 compounds) for 1993 ranged from 249 to 508 pg/m3 for the three sites. Clear seasonality was evident with the highest concentrations occurring during the colder months of October-April, coinciding with the arctic haze period. PAH concentrations during this period were highest in the order of Dunai (Russian) > Alert (high Arctic) > Tagish (Pacific). Air mass back trajectories computed for February 1994 revealed longrange transport from Eurasia into the high Arctic. Short periods of high concentrations were also evident during the warmer months, most notably at the Tagish site, where elevated levels of retene (a marker for soft wood combustion) matched forest fire records. Initial findings suggest that the gas/particle partitioning of some of the lighter PAHs, examined during the colder haze period, is similar to remote temperate studies and in reasonable agreement to the Junge-Pankow adsorption model.
Introduction Over recent decades concern has grown about the levels of persistent organic pollutants (POPs) in the arctic environment (1-3). As part of the Canadian commitment to assessing the occurrence, levels, and pathways of POPs to this region, a multi-year systematic air sampling study was established as part of the Northern Contaminants Program (4). The resulting database has been divided to enable better management, this paper focusing on the PAHs, while subsequent papers will deal with the polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs). PAHs in the arctic environment are present through both anthropogenic and natural sources (petrogenic/biogenic). The influence of these source types has been undertaken through the analysis of sediments taken from the Beaufort and Barents * Author for correspondence. E-mail:
[email protected]; telephone: +416-739-4875; Fax: +416-739-4821. † Atmospheric Environment Service. ‡ Bovar Environmental. § Freshwater Institute. | Institute of Global Climate and Ecology.
S0013-936X(97)00342-8 CCC: $14.00
1997 American Chemical Society
Seas (Arctic Ocean) (5). Aside from riverine inputs of petrogenically derived PAHs, the atmosphere is seen as one of the key sources. Evidence of long-range atmospheric transport from southerly source regions in Eurasia and North America has been demonstrated in both the Norwegian and Canadian Arctic (6-8). Deposition trends of PAHs, evaluated from cores taken from the Greenland ice cap, have shown a dramatic increase in concentrations over the last 100 years that correlate well with the historical record of world petroleum production (9). An increase in the concentration of PAHs relative to those of fatty acids of terrestrial higher plant origin (C20-C32) demonstrated that contributions of anthropogenic PAHs have significantly increased since the 1930s. Similarly, Jaffrezo et al. (10) concluded from surface snow samples, also taken on the Greenland ice cap, that current PAH contamination was essentially due to fossil fuel combustion with some inputs from biomass burning. Over the last 20 years, PAH deposition from the atmosphere to snow and ice layers appears to have remained fairly constant in the Canadian high Arctic (11). This paper focuses on spatial and temporal variations of atmospheric PAHs, collected at sites located in both the Canadian and Russian Arctic. Particular interest was shown in the arctic haze season, which occurs during the coldest time of the year (November-April) and typified by high levels of anthropogenically derived aerosol (12, 13).
Experimental Procedures Air Sampling. Three sites in the Arctic were selected to maximize spatial variation over a wide geographical area. Two of these were located in the Canadian Arctic, Alert on Ellesmere Island (82°30′ N, 62°20′ W) and Tagish in the western Yukon (60°20′ N, 134°12′ W); the third site was located in the Russian Arctic on Dunai Island in eastern Siberia (74°6′ N, 124°30′ E). Figure 1 shows the locations of each of the sites. Weekly sampling commenced at Alert in January 1992, followed by Tagish in December 1992. Sampling at Dunai Island commenced in March 1993. To date, a complete database to the end of 1994 has been compiled for the Alert and Tagish sites, with 1 year of data available for Dunai (March 1993-March 1994). Site maintenance, sampling, sample preparation, extraction, data organization, and preliminary analysis was carried out by Bovar Environmental (BE) in Toronto; sample analysis was performed by the Fresh Water Institute (FWI) in Winnipeg; while data analysis was carried out at the Atmospheric Environment Service (AES) in Toronto. At each site a high-volume (hi-vol) air sampler was operated and fitted with a 10 µm diameter particle size-selective inlet and housing (Wedding and Associates, Fort Collins, CO). Air was drawn through a 20 cm diameter glass fiber filter to trap particulate matter, while two inline (each 4 cm × 20 cm) polyurethane foam plugs (PUFs) were positioned below this to collect the vapor fraction. Flow rates were maintained around 1.13 m3/min by using a critical flow device, resulting in approximately 11 400 m3 of air being aspirated over the course of 7 days. At each site, 52 weekly samples and 13 field blanks were collected each year. Extraction and Analysis. Both PUF plugs and the glass fiber filter were extracted and analyzed separately to obtain information on the respective vapor and particle fractions and to monitor possible analyte breakthrough. Extraction and analytical details have been presented by Fellin et al. (4). In brief, the PUF plugs and filter were extracted for 24 h in hexane and DCM, respectively. Half the extract was archived, while the other half was split again; one fraction undergoing cleanup and analysis for PAHs and the other for organochlorines (the latter compounds will be discussed in subsequent
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FIGURE 1. Location of sample sites within the Arctic. publications). Following cleanup on an alumina:silicic acid column (1:11), PAHs were analyzed on a Hewlett-Packard 5890 gas chromatograph equipped with a mass selective detector (Model HP5970) using a DB5-MS (30 m × 0.25 mm i.d.; 0.25 µm film thickness) capillary column (J&W Scientific). Quantification was performed using the internal standard method, utilizing five deuterated PAHs (100 ng/mL) spiked into the cleaned up extracts. PAH calibration standards of 25, 50, 100, and 250 ng/mL containing all the target PAHs (listed in Table 1) were prepared from stock solution supplied by Supelco Chromatography Products (Oakville, Ontario). Quality Control. Large sample volumes were required to achieve detectable concentrations for a wide variety of target analytes in the arctic atmosphere. Design of the large diameter (20 cm) sampling train (filter + PUFs) ensured that a high flow rate of 1.13 m3/min was maintained. Breakthrough was monitored using a flagging system, which classified a particular sample according to the loadings on the filter (F) and the separate PUF plugs (P1 and P2). Evidence of breakthrough was minimal, with only a few of the lighter PAH exceeding the breakthrough criteria (P2/P1 > 0.333) for several of the samples. Periodically, a second filter positioned downstream of the first was included to monitor the adsorption artifact. Concentrations on the second filters were generally below detection limits, and so this artifact was considered negligible. Field blanks were obtained every 4 weeks and used to generate the minimum detection limits (MDLs), which were derived on an annual basis for each sample site. Table 1 presents a list of the PAH compounds along with the PUF and filter MDLs for 1993; given the different locations and characteristics of sample handling, the MDLs show large variations from site to site, e.g., B[a]P ranges from 0.03 pg/m3 at Dunai (essentially the analytical detection limit) to 0.61 for Alert. As a test for analytical precision, one in every 10 samples was re-analyzed, FWI receiving these as ‘blind’ samples coded by BE. The relative standard deviation ranged from 6 to 25% for the range of PAHs. Analytical recoveries for each sample were corrected by the addition of three deuterated compounds prior to sample cleanup (see Table 1). Overall accuracy was assessed by running NIST certified reference materials and involvement in interlaboratory testing programs. All the data including laboratory data, flags, field comments, and final air volume-corrected concentrations were incorporated into a database.
Results and Discussion Air Concentrations. The ∑PAH mean (geometric) annual air concentrations for Alert were 465 (1992), 444 (1993), and
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330 pg/m3 (1994), while Tagish had concentrations of 194 and 249 pg/m3 for 1993 and 1994, respectively. Dunai in eastern Siberia displayed the highest annual mean concentration of 508 pg/m3 for 1993 (∑ ) 16 compounds listed in Table 1). The more southerly Tagish site experienced the lowest mean annual concentrations out of the three sites, being lower than Alert by a factor of 2.2 and 1.3 for 1993 and 1994, respectively. In previous studies at Alert, Patton et al. (7) reported a ∑PAH mean concentration of 542 pg/m3 (excluding dibenzofuran and biphenyl) for 10 samples taken in February-March 1988. Seasonal Variation. Figure 2 displays a box-and-whisker plot of monthly ∑PAH concentrations (∑ ) 16 compounds) for Alert, Tagish, and Dunai. A seasonal fluctuation in air concentrations was clearly evident, with the colder months of the year (October-April) displaying higher concentrations than the warmer months (May-September). At Alert, the mean ∑PAH concentration during the cold period was an order of magnitude higher than the rest of the year, with elevated concentrations coinciding with the haze period. At this time of year over the arctic region, prevailing meteorological conditions result in the increased incursion of air masses originating from the North American and Eurasian continents. In addition to this, the occurrence of strong temperature inversions in the boundary layer, particularly over the sea ice, prevents the dispersal of pollutants (13). It is likely that these processes also lead to the observed increase in atmospheric PAHs. From Figure 2, sporadic increases in PAH levels were also evident during months outside of the haze season. At Alert, local contamination from the combustion of waste materials and fuels at the nearby military base (14) resulted in elevated concentrations observed between July 20 and August 15, 1993. Furthermore, concentrations at Tagish during August and November 1994 were the highest found at any of the sites. Elevated PAH levels in the Tagish atmosphere during the weeks of August 11-18 and 18-24 coincided with forest fires (5-197 km2) in the southern Yukon (latitude 62-63°N) (15). Retene (1-methyl7-isopropylphenanthrene), a known marker for soft wood combustion (16), comprised >70% of the ∑PAH (∑ ) 19 PΑΗ) concentration during these weeks. Although forest fires were not reported during November, it is likely that the elevated sample week of Nov 24-Dec 1 was due to wood combustion as the PAH profile, marked by high levels of retene (>1 ng/ m3), matched the profile for the August period. Table 2 displays the individual PAH concentrations for the colder winter period (October-April) 1993/1994, along with the corresponding warmer period of May-September 1993. At Alert, however, the warmer period of 1994 has been substituted due to the local contamination event in July/ August 1993. Seasonal variability of phenanthrene, benzo[a]pyrene, and ∑PΑΗ is illustrated in Figure 3 by the comparison of the monthly geometric mean concentrations at Alert for the combined sampling years of 1992-1994. All three parameters have a similar seasonal variation with elevated concentrations during the colder months. Furthermore, analysis of the seasonal PAH profiles showed a significant decline in the contributions by the heavier PAH during the warmer season. Overall, mean concentrations at the high arctic sites of Alert and Dunai were greatly reduced during the warmer period by up to an order of magnitude, with many of the heavier PAHs falling below detection limit. This is a result of either reduced long-range transport (LRT) and/or increased photolytic degradation, the latter being most marked in the high Arctic with the onset of polar sunrise (April), resulting in 24 h of daylight. At Tagish, this seasonal reduction was not as marked (factor of only 2), with several compounds (notably phenanthrene and retene) actually displaying higher levels than the winter. In the Tagish region, during the warmer months of 1993 and 1994, forest fires were numerous and extended up to a latitude of 67° N. It is evident
TABLE 1. PAH Recoveries and Minimum Detection Limits (MDLs) MDLsb for 1993 (pg/m3) PAH (abbreviation) acenaphthylene (ACENPYL) acenaphthene (ACENAP) fluorene (FLUO) phenanthrene (PHEN) anthracene (ANTH) fluoranthene (FLA) pyrene (PYR) retene (RET)c benz[a]anthracene (B[a]A) chrysene (CHR) benzo[b]fluoranthene (B[b]F) benzo[k]fluoranthene (B[k]F) benzo[e]pyrene (B[e]P) benzo[a]pyrene (B[a]P indeno[1,2,3-cd]pyrene (IND-P) dibenz[a,h]anthracene (D[ah]A) benzo[ghi]perylene (B[ghi]P) dibenzothiophene (DBTHPH)c perylene (PERY)c
% recovery range (deuterated PAH)a
101-112 97-114
84-104
Alert
Tagish
Dunai
filter
PUF
filter
PUF
filter
PUF
1.48 1.81 3.11 6.35 0.79 2.35 1.19 1.18 0.91 0.43 4.10 0.13 0.63 0.61 0.18 0.18 0.18 0.43 11.6
3.23 3.08 4.76 8.78 1.67 6.42 6.65 1.95 3.54 1.49 0.96 0.56 1.54 0.67 0.38 0.45 0.52 1.86 0.22
1.86 5.77 18.8 12.9 0.96 0.69 0.88 1.22 1.65 0.47 1.25 0.47 0.46 0.60 1.80 0.01 0.01 2.31 0.40
6.11 11.0 6.28 9.70 0.96 2.37 2.39 1.19 3.33 0.75 0.62 0.53 0.75 0.78 0.01 0.01 0.01 1.85 8.83
0.78 0.84 0.90 1.91 0.38 0.87 1.09 3.72 0.17 0.08 0.03 0.03 0.03 0.03 0.26 0.26 0.26 0.40 0.03
4.44 3.78 3.91 4.71 0.80 1.63 1.67 2.44 1.85 0.38 3.02 1.09 0.76 0.70 0.26 0.26 0.26 1.60 0.44
a Deuterated PAH added to samples. Recovery standards anthracene-d , fluorene-d , benz[a]anthracene-d , (recoveries for Dunai filter and PUF 10 10 12 extracts) Internal standards: naphthalene-d8, acenaphthlene-d10, phenanthrene-d10, chrysene-d12, perylene-d12. b Generated from 13 field blank filters c and PUFs taken throughout each sample year (mean blank + (3 × SD) ) MDL. Not included in the ∑ concentrations.
FIGURE 2. Box-and-whisker plots of ∑PAH concentrations (∑ ) 16 compounds) for each Arctic site: (a) Alert, (b) Tagish, (c) Dunai. Each month comprises of four weekly samples. In each case, the centre box is bounded by the 25th and 75th percentile with the horizontal line representing the 50th percentile or median and the cross depicting the monthly mean. Outliers (g1.5 × interquartile range) are represented by an asterisk. NB, missing months at Dunai indicate operational/logistical problems. that forest fires have a significant impact on atmospheric PAH in the lower arctic regions of northwestern Canada. Long-Range Transport. Lagrangian 5-day back trajectories were computed every 6 h for February 1994 (TRAJPLOT v2.0), the month when all three sites ran concurrently and displayed the highest concentrations. From these trajectories, the mean pathway of air to each site was calculated. This is summarized in Figure 4 for the three arctic sites. Dunai and Alert were strongly influenced by air originating from the Eurasian land mass. In contrast, Tagish, tended to receive air from the Pacific region, air mass back trajectories being calculated at 700 hPa rather than 925 due to the elevation of this site above sea level (∼2200 m). Included in Figure 4 are the average trajectory altitudes: Tagish with its elevated
location tended to receive clean air from aloft relative to the other two sites. PAH concentrations in the atmosphere of the North Pacific have been reported to be the lowest out of any marine or remote study (17). Interestingly, PAH concentrations for this month were highest in the order of Dunai > Alert > Tagish. Indeed, for the whole haze period of 1993/ 1994, PAH concentrations at Dunai were significantly higher than the other two sites (see Table 2). As an example, Figure 5 shows the mean concentrations of phenanthrene (∼50% particulate bound) and benzo[a]pyrene (∼100% particulate bound) for February 1994. Concentrations were approximately 1 order of magnitude higher at Dunai than at Tagish, reflecting the relative proximity of Dunai to major emission sources within the Russian Arctic. This region contains
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a
8.73 (4.88) 6.97 (1.47) 311 (268) 95.5 (61.6) 4.44 (1.90) 78.5 (60.9) 51.4 (38.4)
