Environ. Sci. Technol. 1903, 27,2190-2197
Atmospheric Transport and Transformation of Polychlorinated Dibenzo-pdioxins and Dibenzofurans Mats Tysklind,'gt Ingrid Fangmark,t Stellan Markiund,?Anne Lindskog,* Lennart Thaning,s and Chrlstoffer Rappet
Institute of Environmental Chemistry, University of Ume6, S-901 87 Ume6, Sweden, Swedish Environmental Research Institute, P.O. Box 47086, S-402 58 Goteborg, Sweden, and National Defence Research Establishment, S-901 92 Ume6, Sweden In a study concerning atmospheric transport of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), 14 air samples were collected a t two locations in Sweden. The highest concentrations were measured during sampling events with air masses coming with westerly to southerly winds, indicating long-range transport of PCDDs and PCDFs. Further evidence for long-range transport was shown by the correlation between high levels of PCDDs and PCDFs and SOZ, NOz, Nos-, "3, and soot. The congener profiles were found to vary depending on wind trajectories, implicating source influences from industrialized and urbanized areas in other parts of Europe. By comparison with known source profiles, air samples with a background profile were identified during sampling occasions with air masses coming from the north. Here, the congener profiles were dominated by higher chlorinated congeners. This profile is attributed to transformation processes such as photolytic degradation 01: hydroxyl radical reactions in the gas phase alone or in combination with formation mechanisms.
o Monitoring station
'
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Introduction Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are known to be emitted into the air from various combustion sources and manufacturing processes, such as municipal solid waste incineration, motor vehicles, steel mills, and metal production (1). The emissions from these sources may be transported over long distances and could effect the environment far away from the source itself (2). During transport, wet and dry deposition as well as chemical transformation and degradation may alter the chemical signature of the emission. One way of investigating the transport and transformation processes of PCDD/Fs occurring in the atmosphere and the sources involved is by studying levels, congener profiles, and the isomeric patterns in ambient air. Although PCDD/Fs are considered to be resistant to environmental degradation, snow, rain, soil, and sediment samples show a marked tendency of enhanced concentrations of octachlorodioxin (OCDD) as compared to the other congeners (3, 4 ) . Such a profile cannot be related to any major source of PCDD/Fs known today. One suggested explanation for this enhancement is a combination of volatilization and photodegradation. The lower chlorinated compounds are more rapidly photodegraded, and they are also believed to be predominant in the vapor phase, while the higher chlorinated compounds are as+ University of
UmeL. Swedish Environmental Research Institute. f National Defence Research Establishment. 2190
Envlran. Sci. Technoi., Voi. 27, No. 10, 1993
Figure 1. Location of the field station at Rorvik and the city of Gothenburg.
sociated with the particulate fraction where photochemical reactions are slower ( 5 , 6 ) . Another possible explanation is the gas-phase reactions with hydroxyl radicals, as suggested by Atkinson (3, which will also result in an increased relative proportion of higher chlorinated compounds. Koester and Hites (8) have reported on wet and dry deposition measurements, showing that both deposition routes contribute significantly to the removal of atmospheric PCDD/Fs. For both wet and dry deposition, the higher chlorinated congeners are eliminated most efficiently. Comparisons between congener profiles in atmospheric samples and their possible sources have been carried out previously (3,9-11). Both similarities and differences in congener profiles between atmospheric samples and combustion sources have been reported. Using principal component analysis, Smith et al. (10) were able to distinguish between three classes of air samples having different basic congener profiles, including source-related samples, common background samples, and samples with enhanced levels of lower chlorinated PCDFs. Differences in concentrations and congener profiles of PCDD/Fs in air samples depending on the wind directions have also been reported by Egeback et al. (12). Here, the samples were taken at Hoburgen, Sweden (see Figure 1) on the island of Gotland in the Baltic Sea. This study 0013-936X/93/0927-2190$04,00/0
0 1993 American Chemical Society
Table I. Sample Number, Location, Date, and Weather Conditions no. 1
2 3 4 5 6 7 8 9 10 11 12 13 14 a
location
date
weather conditions"
Rorvik Rorvik Rorvik Rorvik Rdrvik Rorvik Rorvik Rorvik Rorvik Rorvik Rorvik Gothenburg Gothenburg Gothenburg
Jan 27-31,1989 Feb 1-4,1989 Mar 54,1989 May 3-7,1990 May 7-10,1990 May 10-14,1990 May 18-22,1990 May 28-31,1990 Oct 9-11,1990 Oct 11-14,1990 Oct 14-18,1990 June 8-9,1988 June 14-15,1988 Aug 17-18,1988
cloudy, fog, rain S-W cloudy, fog, rain, W-SW cloudy, fog, rain S-WSW-SSE clear skies to partly cloudy, SSW-W cloudy, fog, WSW-WNW cloudy, rain, mixed winds cloudy, mixed winds partly cloudy, rain, NNE-WSW cloudy, rain, SW-W cloudy, fog, W-ESE partly cloudy to cloudy, fog, S-SSE clear skies to partly cloudy, ENE partly cloudy, mixed winds cloudy, fog, ENE-NE
W = west, S = south, E = east, N = north; wind direction at ground level.
showed an increased relative proportion of PCDFs when the air masses were coming from the east. During occasions with westerly to southerly winds, the highest concentrations and more source-related congener profiles were also reported. In this work we studied PCDD and PCDF levels and congener profiles in ambient air samples collected at a rural area, Rorvik, Sweden, during 1989 and 1990, in relation to the origin of the air as given by trajectories. These samples are also compared with air samples collected in the city of Gothenburg, Sweden, in 1988, as well as with other earlier reported data on PCDD/Fs in ambient air samples from these two locations. We have classified air samples according to the congener profiles found in the emissions from various sources. A consideration of the classes suggested by Smith et al. (10) is also included for comparison to this study. Experimental Section Sampling. Ambient air samples were collected using a high-volumesampler at Rorvik and Gothenburg. Rorvik is a research station located in a rural area on the Swedish west coast, situated about 40 km south of the city of Gothenburg. It is also a monitoring station operating within both the European Monitoring and Evaluation Program (EMEP) and the Tropospheric Ozone Research project (TOR). Gothenburg is a medium-sized industrialized city located at the coast, having approximately 350 000 inhabitants. These sampling locales are indicated in Figure 1. A glass fiber filter (160GM, 8 = 142 mm, Munktell, Gryxbo, Sweden) followed by two prewashed polyurethane foam plugs (PUF, 110 X 50 mm2) (13) were used to collect airborne particles as well as vapor-phase PCDD/Fs. Before sampling, the filters were spiked with 13C-labeledinternal standards, viz. 2,3,7,8-TCDF,2,3,7,8TCDD, 2,3,4,7,8-PeCDF,1,2,3,7,8-PeCDF,1,2,3,4,7,8-HxCDF, 1,2,3,6,7,&HxCDD,1,2,3,4,6,7,8-HpCDF,1,2,3,4,6,7,8HpCDD, and OCDD (Cambridge Isotopes Lab., Wolburn, MA), to determine the sampling efficiencies and to compensate for losses that occurred during the sampling and analytical procedure. Approximately 1500 m3 of air were collected for each sample, correspondingto a sampling period of 3-5 days. A summary of the 14samples collected, their locations, and weather conditions during sampling events is given in Table I. Cleanup and Analysis. The filter and foam plugs were combined in a Soxhlet extractor and spiked with other
labeled compounds used as cleanup spikes, viz. 37C1-labeled 2,3,7,8-TCDD and 13C-labeled 1,2,3,7,8,9-HxCDD and 1,2,3,7,8,9-HxCDF. The concentrated extracts were thereafter purified according to the method described by Marklund (14)using a sulfuric acid on silica gel column followed by a column of aluminium oxide. The final quantitative analysis was performed by HRGC/HRMS using a 60-m Supelco 2330 fused silica column (Supelco, Inc., Bellefonte, PA) and a VG 70-250 instrument running in EI+ mode. The capillary column was temperature programmed as follows: 180 "C initial for 2 min, increased at 3 "C/min to an isothermal hold at 260 "C. The sample introduction was achieved by splitless injection at 250 "C. Tetra- through octachlorinated PCDDs and PCDFs were monitored to their known GC elution times for the above chromatographic conditions. Quantification was done by comparisonbetween peak areas of the native compounds and 13C-labeledinternal standards. The toxic 2,3,7,8-substituted congeners were quantified as well as the totals for the tetra- to octachlorinated homologue groups. Other Pollutants and Meteorological Data. Data on the concentrations of air pollutants are recorded within the EMEP and TOR projects, which were available for use in this study. SO2, S042-,NO2, NOS-, "3, and soot were given as 24-h means. Meteorological parameters including temperature, relative humidity, ground wind speed, and wind direction were also taken simultaneously. These meteorological data and the mean concentrations of the pollutants for each sampling period are presented in Table 11. The mean values are based on eight observations each 24-h period, where each observation represents the mean of 10 min. Ozone was measured using UV-adsorption (Monitor Labs model 8810), and nonmethane hydrocarbons (NMHC, ( 2 2 4 5 ) were measured using an automatic gas chromatographic system with 20min samples collected every 4 h (15). Trajectory calculations (isobaric) were made for all 11 sampling events at Rorvik at 850,900,925, and 950 hPa in order to determine the origin of bulk air masses and possible PCDD/Fs origins. Wind data from the European Center for Median Range Weather Forecasts (ECMWF) (16) were used as input to the trajectory model developed by KAllberg (17). Two sets of trajectories were calculated for each day, one for air arriving at the sampling site at 12 GMT and another for air arriving at 00 GMT. All trajectories were calculated backwards in time out to -72 Envlron. Sci. Technol., Vol. 27, No. 10, 1993 2191
Table 11. Meteorological Parameters and Mean Concentrations of Inorganic Pollutants sample no. 1 2
3 4 5 6 7 8 9 10 11 12
13 14
T,O C 5.7 5.7 7.1 13.8 15.3 11.6 9.5 9.9 11.5 10.9 12.5 19.8 15.3 8.4
precipitation, mm
relative humidity, %
wind speed, m/s
0.8 17.3
85.5 87.3 81 60.5 66.3 76.2 53 63.3 80 82.5 87.7 65 52 84
7.5 6.7 6 2.5 1.5 3.9 3.8 3.4 8.2 3.9 3 6.2 4.2 4.5
0.1 0
0 59.4 0 6.2 3.1 0 0 0 0 0
h for identification of air mass history. It is not possible to give a general estimation of the errors in the trajectory calculations since they are strongly dependent on the weather situation. A major source is the lack of realistic vertical movements, which in situations with a strong vertical windshear, e.g., at a front of a low-pressuresystem, may cause a substantial uncertainty. However, in situations characterized by small windshear, the error becomes small. The reason for calculating trajectories at four heights was to keep track of the uncertainty, since if the divergence of such a set of trajectories is small, the source area may be identified. In this study, the sampling events are all characterized by small divergence in each set of trajectories. Data Analysis. Principal component analysis (PCA) (18) was used to evaluate possible similarities and/or differences in the congener profiles of PCDD/Fs in the air samples as well as the composition of inorganic pollutants during each sampling event. PCA in effect reduces several variables down to a few underlying descriptive dimensions, through summarizing systematic information present in the data. Prior to PCA, it is important to decide upon some needed type of preprocessing of data. Here the primary interest is the composition of different congeners appearing in individual air samples and how these congener profiles correlate to known sources. Hence, in order to eliminate the concentration figures as a major component of variation in the first principal component, it was necessary to perform a normalization of the data to the total concentration of PCDD/F in each sample. Prior to the data analysis, the data were also preprocessed by means of auto-scaling and mean-centering. For further discussion, see Schwartz and Stalling (19). All calculations were performed on an IBM PS2 computer using the SIMCA 4.3R program (Umetri AB, S-901 24 Umel, Sweden). Results and Discussion PCDD and PCDF Levels. The concentrations of the 2,3,7,8-substituted congeners, the concentrations of the sum of the homologue groups, the sum of the total tetrato octachlorinated PCDD/Fs, and the ratio of PCDFs/ PCDDs are given in Table 111. The total levels of PCDD/ Fs measured in the rural station at Rorvik are found to be between0.3 and 5.2 pg/m3. The highest levels are found in samples collected during episodes with westerly to southerly winds. In the samples collected at Rorvik (samples 1-11),the lowest total levels of PCDD/Fs were found in samples from May 1990. The results reported 2102
Environ. Scl. Technol., Vol. 27, No. 10, 1993
so2-s, sop-s, Pdm3
Pdm3
2.8 4.2 9.6 1.4 1.8 0.8 0.5 1.3 1.7 3 3.9
1.2 3.3 3.5 1.8 4.2 2.4 1.8 2.6 0.6 2.3
0.8
1.8 0.3 0.8
0.8 1.6
2.1
NOZ-N, wdm3
N03--N, rdm3
NHs-N, rg/m3
5.3 3.3 1.9 2.5 2.2 1 0.9 1.2 0.9 2 2.8 1.4 1.7 1.7
1.4 1.6
2.2
1.2 1 1.2
0.4 0.2 1
0.2 1
1.9 0.5 0.4
2.3 3
soot,
pg/m3 6.2 6 6.8
1.2
2.2
2.4 0.9 0.4 1.5 0.5 3 3.1 1.3 0.5 0.6
4.8 1.8 2.2
1.5 1 11
12.5 3 1.5 3.5
here are in good agreement with earlier measurements at Rorvik (20,21),see Table IV. In most samples the PCDDs are found at higher concentrations than the PCDFs. The three samples from Gothenburg (samples 12-14) show levels in the same general range as the Rorvik samples (a variation between 1.0 and 1.8 pg/m3). These results are somewhat lower than levels earlier reported from Gothenburg (2.4-13.4 pg/m3) (20,21). In Table IV, the total concentrations of PCDD/Fs measured at Rorvik and Gothenburg are compared with literature data from other locations in Sweden a5 well as from locations in other countries. The total concentration of PCDD/Fs varies from background levelsof less than 1to 100 pg/m3in heavy industrialized areas. Congener Profiles. The congener profiles found in the collected samples were compared by PCA. The relative distribution of the totals of each congener group, as calculated from Table 111, was used in the PCA. Two principal components accounted for a total of 42% (26% + 16%) of the variance in the data set. The resulting score plot, the first principal component versus the second, and bar graphs for each individual sample are presented in Figure 2. Moving from the right to the left in the plot, four different clusters found in the samples could be identified. To the right we find samples with a high relative concentration of OCDD, i.e., samples 4 , 5 and 7. In these samples the total levels of PCDD/Fs are low. Sucha profile is similar to that found in samples of rain and sediments (5,21). This profile has been considered to be representative for background air samples which have been subjected to “aging”during transport. All other samples seem to be more or less influenced by local or regional sources. Moving to the left and to the upper end of the plot, the concentrations of tetrachlorodibenzofurans (TCDFs) increase, resulting in a profile dominated by both OCDD and TCDFs, Le., samples 6, 8 and 12. The total concentrations of PCDDs and PCDFs are relatively low. In the lower part of the plot, the PCDDs are the dominating group with not only the OCDD but also the heptachlorodioxins (HpCDDs) and hexachlorodioxins (HxCDDs). To the far left we find samples 1-3, all containing the highest total level of PCDD/Fs and a relative congener profile with both PCDD/Fs. In these samples we find higher chlorinated PCDF congeners as well. Noteworthy is the high relative concentration of HpCDFs, which has also been seen in air and deposition samples at other locations (27). The concentration of OCDF is generally low in all samples.
Table 111. Levels of PCDDs and PCDFs in Ambient Air Samples Collected at Rorvik and Gothenburg, Sweden (pg/m8) 1
3
2
4
5
6
sample 7 8
9
1
0
1
1
0.017 0.02 0.004 0.008 0.003 0.002 0.004 0.003 0.010 0.011 2,3,7,8-TCDF 0.024 0.50 0.095 0.13 0.083 0.036 0.11 0.087 0.18 0.24 0.52 0.47 total TCDF 0.004 0.003 0.002 0.004 0.002 0.001 0.002 0.002 0.002 0.002 2,3,7,8-TCDD 0.004 0.17 0.085 0.036 0.041 0.031 0.016 0.037 0.045 0.051 0.081 total TCDD 0.28 0.028 0.019 0.003 0.004 0.002 0.001 0.003 0.005 0.011 0.014 1,2,3,7,8-PeCDF 0.029 0.021 0.002 0.003 0.002 0.001 0.002 0.004 0.011 0.012 0.031 0.022 2,3,4,7,8-PeCDF 0.33 0.28 0.032 0.031 0.020 0.011 0.026 0.057 0.12 0.17 total PeCDF 0.32 0.011 0.005 0.001 0.002 0.001 0.001 0.001 0.003 0.005 0.008 1,2,3,7,8-PeCDD 0.013 0.09 0.026 0.018 0.015 0.010 0.020 0.062 0.064 0.093 0.19 0.18 total PeCDD 0.002 0.004 0.005 0.003 0.002 0.004 0.008 0.015 0.019 0.049 1,2,3,4,7,8-H~CDF 0.040 0.033 0.007 0.003 0.004 0.002 0.001 0.003 0.006 0.010 0.015 1,2,3,6,7,8-H~CDF 0.031 1,2,3,7,8,9-H~CDF
