Observed trends for CF3-containing compounds in background air at Cape Meares, Oregon, Point Barrow, Alaska, and Palmer Station, Antarctica

Chemosphere 55 (2004) 1109–1119 www.elsevier.com/locate/chemosphere

Observed trends for CF3-containing compounds in background air at Cape Meares, Oregon, Point Barrow, Alaska, and Palmer Station, Antarctica J.A. Culbertson a, J.M. Prins a, E.P. Grimsrud a,*, R.A. Rasmussen b, M.A.K. Khalil c, M.J. Shearer c a

Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA Department of Environmental and Biomolecular Systems, OGI School of Science and Engineering, Oregon Health and Science University, 20000 NW Walker Road, Beaverton, OR 97006, USA c Department of Physics, Portland State University, P.O. Box 751, Portland, OR 97207-0751, USA b

Received 27 January 2003; received in revised form 28 July 2003; accepted 3 November 2003

Abstract The concentrations of CF3 -containing compounds in archived air samples collected at Cape Meares, Oregon, from 1978 to 1997, at Point Barrow, Alaska, from 1995 to 1998, and at Palmer Station, Antarctica, from 1991 to 1997, were determined by high resolution gas chromatography and high resolution mass spectrometry. The CF3 -containing compounds measured by this method and discussed here are: the perfluorinated compound, C3 F8 (FC 218); four perhalogenated compounds, CF3 Cl (CFC 13), CF3 CF2 Cl (CFC 115), CF3 CFCl2 (CFC 114a), and CF3 Br (Halon 1301); and three hydrofluorocompounds, CF3 H (HFC 23), CF3 CH3 (HFC 143a), and CF3 CH2 F (HFC 134a). For four of these compounds, very few measurements have been previously reported. The atmospheric concentrations of all of the CF3 -containing compounds continuously increased in time over the sample collection periods. From these data, the annual rates of emission into the atmosphere have been estimated. The emission rates fall into one of three distinct categories. The annual emission rates of C3 F8 , CF3 H, CF3 CH3 , and CF3 CH2 F have continuously increased over the last two decades. That of CF3 CFCl2 has decreased continuously. Emission rates for CF3 Cl, CF3 CF2 Cl, and CF3 Br reached maximum levels in the late 1980s, and have been decreasing in the 1990s. The emission rates of C3 F8 , CF3 CH3 and CF3 CH2 F were nearly zero 20 years ago but have increased rapidly during the last decade.
2003 Elsevier Ltd. All rights reserved. Keywords: CF3 trace gases; Halons; HCFC; CFC; CF3 Br; HRGC–HRMS measurements

1. Introduction Since the 1970s, attention has been focused on the significance of a wide variety of halogenated compounds known to be increasing in the Earth’s atmosphere, and especially on the effects of these compounds on the

*

Corresponding author. Tel.: +1-406-994-5418; fax: +1-406994-5407. E-mail address: [email protected] (E.P. Grimsrud).

destruction of ozone in the stratosphere (Molina and Rowland, 1974; McElroy and Salawitch, 1989; Fisher et al., 1990a; Prather and Watson, 1990; Solomon et al., 1992) and on global warming (Schneider, 1989; Fisher et al., 1990b; Ravishankara et al., 1993; Daniel et al., 1995). A challenging aspect of research in this area has been to measure the individual halogenated compounds in air samples. In addressing this need, we have developed and demonstrated a powerful method of analysis based on high resolution mass spectrometry (HRMS) along with gas chromatography (GC) (Engen et al.,

0045-6535/$ - see front matter
2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2003.11.002

1110

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

1998, 1999; Culbertson et al., 2000). In the present paper, we report the application of this method to the analysis of CF3 -containing compounds in historic air samples collected at Cape Meares, Oregon, from 1978 to 1997, at Point Barrow, Alaska, from 1995 to 1998, and at Palmer Station, Antarctica, from 1991 to 1997. The ten compounds measured (eight reported here) represent various classes of halogenated compounds, including chlorofluorocarbons (CFCs), bromofluorocarbons (Halons), hydrochorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). All of these are believed to be manmade. The data set acquired provides a means of assessing the effects of man’s activities in releasing these compounds to the earth’s atmosphere.

2. Experimental A detailed description of the high-resolution chromatographic and mass spectrometric analysis system with its sample introduction procedure has recently been published (Engen et al., 1998, 1999; Culbertson et al., 2000). Only a brief description of its primary components will be given here. The high-resolution mass spectrometer is a ZAB-2F (VG Instruments) of the dualsector design with an accelerating voltage up to 8 kV. The gas chromatograph (Hewlett-Packard, Model 5890 series II Plus) has sub-ambient temperature capability with liquid N2 cooling. The gas chromatograph contains a high-resolution GS-GasPro (J&W Scientific, Folsom, CA, USA) PLOT column of 30 m in length and 0.32 mm in internal diameter. This coupled system is referred to here as HRGC–HRMS. Aliquots of historic air samples were obtained from Prof. R.A. Rasmussen’s 20-year collection of archived samples housed at the OGI School of Science and Engineering. The archive consists of samples taken between 1977 and 1997 using an in situ air liquefaction method to compress about 1000 l of air at STP to 450 psig and store it in 33 l stainless steel tanks internally passivated by the SUMMA process. The samples were transported to Montana State University in 850 ml internally electro-polished stainless-steel canisters which had been filled to a pressure of about 30 psig. As a reference standard, a large volume contemporary air sample was collected 10 km south of Bozeman, Montana, in March 2000. It was collected using an oil-less diaphragm pump (KNF Neuberger, model N05SVI) and a 33 l canister that also had been treated by the SUMMA electro-polishing process. The tank was filled to a pressure of 40 psig. Air samples were introduced to the HRGC–HRMS system by a preconcentration procedure. For each sample analyzed, a volume of 355 cm3 (corrected to standard conditions of pressure, 1.00 atm, and temperature, 25 C) was drawn through a freeze-out loop that consisted of a short

length of a GS-GasPro column (22 cm · 0.32 mm), which was cooled to liquid nitrogen temperature. Moisture in the air sample was removed prior to the freeze-out by passage through a short drying tube containing Mg(ClO4 )2 . This was found to be necessary in order to prevent plugging of the loop and GC column by ice. After the preconcentration step, the loop was rapidly warmed by a heat gun and its contents transferred to the HRGC via a six-port valve. The initial temperature of the GC oven was held at )40 C for 4 min and then increased at a rate of +20 C/min to the final temperature of 180 C. The carrier gas (ultrahigh purity He) inlet pressure was held constant at 12 kPa. The exit end of the GC column was threaded directly into the ion source of the HRMS. The mass spectrometer was operated in a selected ion mode in which the CFþ 3 ion (m=z ¼ 68:9952) was monitored with the mass resolution set to a level of 2200. To ensure that the mass spectrometric measurements were made exactly on the centroid of the selected mass, the mass scale of the mass spectrometer was recalibrated twice per second by use of the mass reference ions produced simultaneously from the constant addition of dodecane to the ion source (Engen et al., 1998). Analysis of a Montana rural air sample using the CFþ 3 single-ion monitoring technique to establish the absolute calibration is described in Culbertson et al. (2000). Ten CF3 -containing compounds are detected in the historic samples analyzed in this study. By comparing the peak areas of the historic air samples to that of the contemporary reference air sample, the relative concentrations of the ten compounds were determined in the historic samples. A usable volume of 100 l was contained in the reference air tank. The absolute concentrations of each CF3 -containing compound in background air at the time of collection of the reference sample were determined using a large volume (9454 l) chamber with the standard additions method (Engen et al., 1999; Culbertson et al., 2000). From these analyses, the concentrations in the reference sample of the eight gases discussed here were determined to be: 0.26 ± 0.03 pptv for C3 F8 , 3.6 ± 0.4 pptv for CF3 Cl, 7.9 ± 0.8 pptv for CF3 CF2 Cl, 7.9 ± 0.8 pptv for CF3 CFCl2 , 2.2 ± 0.2 pptv for CF3 Br, 12.4 ± 2 pptv for CF3 H, 3.2 ± 0.5 pptv for CF3 CH3 , and 21 ± 2 pptv for CF3 CH2 F. The relative uncertainties in the absolute concentrations within our standard are thought to be about ±10% for most compounds, while that of CF3 H is somewhat greater, about ±18%. These uncertainties were determined from our estimates of the systematic errors associated with the preparation of our primary standards from the pure gases and from the least-squares analysis of each standard addition experiment (Engen et al., 1999). In the subsequent analysis of all historic air samples, at least two analyses of each air sample and at least two analyses of the reference sample were made during the

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

course of a single day’s measurements. Generally, the average of these paired measurements was then used for the determination of each sample. Statistical analysis of the paired measurements also provided a measure of the standard deviations of the method for all compounds (Peters et al., 1974). For a randomly selected set of 30 paired measurements of this type, the standard deviations of the method were found to be: 0.014 pptv for C3 F8 , 0.15 pptv for CF3 Cl, 0.24 pptv for CF3 CF2 Cl, 0.5 pptv for CF3 CFCl2 , 0.13 pptv for CF3 Br, 1.4 pptv for CF3 H, 0.17 pptv for CF3 CH3 , and 0.90 pptv for CF3 CH2 F. The compounds are all assumed stable in the archive. All of the gases are manmade and non-reactive (lifetimes ranging from 15 to 50 000 yr), and are unlikely to be destroyed or created in the passivated containers. Because these compounds can only be measured by recent technology, the stability of the compounds in the containers cannot presently be demonstrated by re-measurement.

1111

3. Results and discussion Of the historic air samples analyzed, 210 were collected at Cape Meares, Oregon, from 1978 to 1997, 71 samples were collected at Point Barrow, Alaska, from 1995 to 1998, and 108 samples were collected at Palmer Station, Antarctica, from 1991 to 1997. The number of samples available per year ranged from 23 in 1989 to 1 sample in 1991. Table 1 gives the annual average concentrations for all gases. 3.1. Concentrations and trends 3.1.1. Perfluorocarbons Results and discussion of CF4 and C2 F6 concentrations measured from the historic samples are provided in Khalil et al. (2003). The observed mixing ratios for C3 F8 (FC 218) are shown in Fig. 1. In Fig. 1A, the concentrations in Oregon increase from about 0.07 pptv in 1978

Table 1 Annual average concentrations of CF3 -containing trace gases in parts per trillion by volume (pptv) Mid-year

C3 F 8 (pptv)

CF3 Cl (pptv)

CF3 CF2 Cl (pptv)

CF3 CFCl2 (pptv)

CF3 Br (pptv)

CF3 H (pptv)

CF3 CH3 (pptv)

CF3 CFH2 (pptv)

Cape Meares, 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991a 1992 1993 1994 1995 1996 1997

Oregon 0.08 0.07 0.08 0.08 0.09 0.08 0.09 0.09 0.11 0.12 0.14 0.13 0.14 0.14 0.14 0.16 0.18 0.20 0.19 0.22

1.5 1.6 1.7 1.9 1.9 2.1 2.1 2.3 2.6 2.8 2.8 3.1 3.1 3.2 3.2 3.3 3.5 3.5 3.6 3.4

1.6 1.9 2.0 2.4 2.5 2.9 3.0 3.7 4.1 4.3 4.7 5.5 6.0 6.1 6.2 6.8 7.2 7.3 7.5 7.7

4.6 4.7 4.9 5.2 5.5 5.7 5.8 6.0 6.5 7.1 7.4 7.6 7.9 7.5 7.1 7.7 8.1 7.7 8.2 8.3

0.3 0.3 0.4 0.5 0.6 0.6 0.7 0.9 1.0 1.2 1.3 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.2 2.3

4.0 4.8 4.8 5.9 5.3 6.4 5.7 5.9 6.9 7.0 8.3 9.4 9.0 9.0 9.0 9.9 10.1 12.3 12.4 13.1

0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.4 0.5 0.6 0.6 0.7 0.7 0.8 0.9 1.1 1.4 1.9

0.1 0.2 0.2 0.3 0.4 0.7 1.6 2.6 3.3 4.8

Point Barrow, Alaska 1995 0.21 1996 0.20 1997 0.23

3.9 3.6 3.6

7.8 7.9

8.7 8.4 8.3

2.4 2.4 2.3

12.2 14.2 14.1

1.2 1.5 1.7

2.4 3.7 5.3

6.5

8.4

2.1

9.8

0.7

0.4

7.2 7.2 7.4 7.7

9.1 8.5 8.4 8.4

2.2 2.1 2.2 2.3

11.6 11.7 12.5 13.9

0.8 0.9 1.0 1.3

0.6 1.0 2.0 2.9

Palmer Station, Antarctica 1992 0.15 1993 1994 0.16 1995 0.16 1996 0.18 1997 0.19 a

3.5 3.5 3.5 3.6

Concentrations in 1991 are interpolated, due to lack of data throughout that year.

1112

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119



Fig. 1. (A) Mixing ratios ( ) and the best-fit trend line (dark line) for C3 F8 found in samples collected at Cape Meares, Oregon. (B) Mixing ratios in samples collected at Palmer Station, Antarctica ( ), and at Point Barrow, Alaska (N), for C3 F8 , compared to the trend line from Cape Meares.

to about 0.20 pptv in 1997. In about 1986, the growth rate increased significantly to a level of about 0.012 pptv yr1 . The presence of C3 F8 in the atmosphere is possibly due to its use for plasma etching in the semiconductor industry (Pruette et al., 1999). In Fig. 1B, the mixing ratios for C3 F8 found in the samples collected in Alaska and Antarctica are shown along with the polynomial fit to the Cape Meares data. The difference between the Arctic and Antarctic concentrations can be explained by transport time between hemispheres, with no additional significant sinks in the troposphere. 3.1.2. Perhalogenated chloro- or bromocompounds Fig. 2 shows the time series of mixing ratios of four perhalogenated compounds at Cape Meares, Oregon: chlorotrifluoromethane (CF3 Cl, CFC 13) in Fig. 2A; chloropentafluorethane (CF3 CF2 Cl, CFC 115) in Fig. 2B; 1,1-dichlorotetrafluoroethane (CF3 CFCl2 , CFC 114a) in Fig. 2C; and bromotrifluoromethane (CF3 Br,



Fig. 2. Mixing ratios ( ) and polynomial fit lines (dark lines) for four perhalogenated bromo- or chlorocompounds found in Oregon samples: (A) For CF3 Cl, along with previous measurements by ( ) Rasmussen and Khalil (1980), (M) Penkett et al. (1981), () Fabian et al. (1996), ( ) UEA (Montzka et al., 2003). (B) For CF3 CF2 Cl, along with previous measurements by (M) Penkett et al. (1981), ( ) Pollock et al. (1992), ( ) Schauffler et al. (1993), () Fabian et al. (1996), ( ) Sturges et al. (2000), (thin model line) by Daniel et al. (1996), and (}) AGAGE (Sturrock et al., 2001; Montzka et al., 2003). (C) For CF3 CFCl2 , along with an early measurements by () Rasmussen (NASA, 1994), and (M) Sturges et al. (2000). (D) For CF3 Br, along with previously reported data by (M) Fraser et al. (1999) and () Montzka et al. (1999).



J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

Fig. 3. Mixing ratios in samples collected at Palmer Station, Antarctica ( ), and Point Barrow, Alaska (N), for (A) CF3 Cl, (B) CF3 CF2 Cl, (C) CF3 CFCl2 , and (D) CF3 Br.

Halon 1301) in Fig. 2D. Fig. 3 shows the same gases at Pt. Barrow, Alaska and Palmer Station, Antarctica. Mixing ratios for CF3 Cl in the Oregon samples are shown to increase from about 1.3 pptv in 1978 to about 3.5 pptv in 1997. An increase in growth rate from about 0.060 pptv yr1 (4.6% yr1 ) in 1978 to about 0.15

1113

pptv yr1 (7.5% yr1 ) in 1984 was observed. From 1985 to 1991, the growth rate remained constant at about 0.16 pptv yr1 and then steadily decreased, reaching near zero growth by 1997. To our knowledge, only four previous measurements of CF3 Cl have been reported. These are also shown in Fig. 2A and are not in close agreement with the present set of measurements, except for the University of East Anglia (UEA) (Montzka et al., 2003) which is on the polynomial fit shown. In Fig. 3A, the CF3 Cl concentrations in the Alaska and Antarctica samples are nearly identical to each other and to those collected in Oregon at the same times, indicating that CF3 Cl is was very well mixed throughout the atmosphere in the 1990s. In Fig. 2B, mixing ratios for CF3 CF2 Cl in the Oregon samples increase from about 1.6 pptv in 1978 to about 7.6 pptv in 1997. An increase in growth rate from about 0.11 pptv yr1 (6% yr1 ) in 1978 to about 0.43 pptv yr1 (7% yr1 ) in 1990 was observed. After 1990, the growth rate continuously decreased reaching a minimum value of 0.13 pptv yr1 (1.8% yr1 ) in 1997. The thin line in Fig. 2B indicates the trend line previously reported by Daniel et al. (1996) for measurements made between 1982 and 1994. Also shown are a scattering of data points from 1978 to 1996, measured by several different research groups, and a recent time series of measurements from the AGAGE program at Cape Grim, Australia (Sturrock et al., 2001). The later mixing ratios match ours quite well. As in the case of CF3 Cl described above, the mixing ratio of CF3 CF2 Cl in the samples collected in Alaska and Antarctica (Fig. 3B) are nearly identical to each other and to those collected in Oregon at the same times. Fig. 2C shows that the mixing ratio for CF3 CFCl2 in the Oregon samples has increased from about 4.6 pptv in 1978 to about 8.0 pptv in 1997. A steadily decreasing growth rate from about 0.35 pptv yr1 (7.5% yr1 ) to near zero was observed from 1978 to 1997. At present, only two other measurements of this compound are available for comparison: earlier unpublished data of Rasmussen showed an approximate tropospheric CF3 CFCl2 concentration of about 5 pptv in 1990; and Sturges et al. (2000) who reported a concentration of about 1.8 pptv in 1994, neither close to our data. Again, in Fig. 3C measurements of the samples collected in Alaska and Antarctica indicate that CF3 CFCl2 is very well mixed throughout the entire atmosphere as expected by its low growth rate during the 1990s. Fig. 2D indicates that the mixing ratio of CF3 Br in the Oregon samples increased from about 0.3 pptv in 1978 to about 2.4 pptv in 1997. The absolute growth rate of CF3 Br increased from about 0.044 pptv yr1 (15% yr1 ) in 1978 to about 0.15 pptv yr1 (10% yr1 ) in 1990. After 1990, the growth rate decreased, falling back to about 0.03 pptv yr1 (1.3% yr1 ) by 1997. There have been numerous previous reports on CF3 Br

1114

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

measurements in the atmosphere (e.g., Penkett et al., 1981; Khalil and Rasmussen, 1985; Singh et al., 1988; Gunawardena, 1989; Butler et al., 1992; Fraser et al., 1999; Montzka et al., 1999; Schauffler et al., 1999). The extensive set of measurements from Cape Grim, Tamania (Fraser et al., 1999) and global average data from NOAA CMDL (Montzka et al., 1999) are also shown in Fig. 3D and are in good general agreement with ours. Also, Butler et al. (1992) reported an average growth rate from various sampling sites of 0.14 pptv yr1 between 1989 and 1992 and this agrees well with our value of about 0.15 pptv yr1 for 1990. Their report of a lower global growth rate of 0.044 pptv yr1 from mid-1995 to 1996 is also in good agreement with our determination of 0.05 pptv yr1 for the Oregon samples over that time period. In Fig. 3D, no significant difference is indicated in the mixing ratios of the samples collected in Antarctica and Alaska during the mid- to late-1990s, indicating this compound is well mixed throughout in the entire atmosphere. This result is expected due to the lowered annual emissions of this compound in the 1990s. The Antarctica measurements yielded an average growth rate of 0.55 pptv yr1 from 1992 to 1997, similar to Butler et al.’s (1998) measurement of 0.51 pptv yr1 during this period for the southern hemisphere. Fraser et al. (1999) have reported a further reduction of growth in the southern Hemisphere to 0.03 pptv yr1 in 1998. 3.1.3. Hydrofluorocompounds Fig. 4 shows the time series of three hydrofluorocarbons at Cape Meares, Oregon: trifluoromethane (CF3 H, HFC 23); 1,1,1-trifluoroethane (CF3 CH3 , HFC 143a); and 1,1,1,2-tetrafluoroethane (CF3 CH2 F, HFC 134a). Fig. 5 shows the corresponding concentrations at Pt. Barrow, Alaska, and Palmer Station, Antarctica. In Fig. 4A, the mixing ratios for CF3 H in the Oregon samples are shown to increase from about 4.0 pptv in 1978 to about 13.5 pptv in 1997. The growth rate of CF3 H was constant at about 0.35 pptv yr1 from 1978 to 1986, after which a steady increase occurred, reaching a level of 0.69 pptv yr1 (5.0% yr1 ) by 1997. Oram et al. (1998) have made extensive measurements of CF3 H in samples collected in the southern hemisphere (Cape Grim, Tasmania) between 1978 and 1995 and as shown by the thin line in Fig. 4A, there is good agreement in the trends established by the two sets of measurements. The fact that the measurements of Oram et al. are consistently about 1.2 pptv below those of the present study might be due in part to small systematic errors in the calibration methods used and, to a slightly lower concentration expected in the southern hemisphere, when the main sources are in the northern hemisphere. Until the recent phase-out of halons by the Montreal Protocol, CF3 H was used primarily as a raw material in the production of CF3 Br. Today, a main source of CF3 H is



Fig. 4. Mixing ratios ( ) and polynomial lines (dark lines) for three hydrofluorocompounds found in the Oregon samples. (A) For CF3 H, along with data (M) and model line (fine line) reported by Oram et al. (1998). (B) For CF3 CH3 . (C) For CF3 CH2 F, along with model line (fine line) reported by Montzka et al. (1996), and AGAGE data (M) from Mace Head, Ireland (Simmonds et al., 1998; Prinn et al., 2000).

thought to be as a by-product in the industrial production of CHClF2 (HCFC 22) while small amounts are used in the plasma etching of semiconductors, as a low temperature refrigerant, and as a fire extinguishing agent (Oram et al., 1998). In Fig. 5A, the mixing ratios for CF3 H found in the samples collected in Alaska and Antarctica do not show significant differences. However, it was noted in this study that CF3 H measurements had a significantly higher degrees of scatter upon multiple repetitive analyses of the same sample (about 12% RSD) than any other compound in this study. Therefore, due to a lack of measurement precision in this case, it is possible that a difference between northern and southern hemispheric

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

Fig. 5. Mixing ratios in samples collected at Palmer Station, Antarctica ( ), and Point Barrow, Alaska (N), for (A) CF3 H, (B) CF3 CH3 , and (C) CF3 CH2 F.

measurements exists, but is not clearly delineated in this data set. In Fig. 4B, the mixing ratios for CF3 CH3 in the Oregon samples are shown to increase from about 0.2 pptv in 1978 to about 2.0 pptv in 1997. An increase in its growth rate to about 0.04 pptv yr1 began in 1984 and continued until 1992. Between 1993 and 1997, the growth rate then further increased to a level of about 80% yr1 by 1996 and 1997. To our knowledge, measurements of CF3 CH3 in the atmosphere have not been reported outside of our earlier work (Culbertson et al., 2000). In Fig. 5B, significant differences in the mixing ratios for CF3 CH3 are noted between the samples collected in Alaska and Antarctica. This compound is currently being used as a CFC replacement (Hayman and Der-

1115

went, 1997), and the difference in concentrations is expected due to the very recent and rapidly increasing emissions of this compound into the northern hemisphere. In Fig. 4C, the mixing ratio for CF3 CH2 F in the Oregon samples was not detectable until late 1988, and by 1993 was exhibiting an exponential growth of approximately 100% yr1 . Previous measurements of CF3 CH2 F have been made by Montzka et al. (1996), Oram et al. (1996), and Simmonds et al. (1998). The same general trend of increasing concentration and increasing growth rates were observed in all of these studies. The first two studies examined air samples from both the northern and southern hemispheres from the late 1980s to 1995. Analysis of samples from Mace Head, Ireland, by Oram et al. (1996) from mid-1994 to mid-1995 gave a growth rate of 1.24 pptv yr1 , somewhat greater than our measured growth rate in Oregon of 1.0 pptv yr1 for that year. Simmonds et al. (1998) has also made measurements at Mace Head, Ireland from 1994 to 1997. They reported a growth rate of 2.05 ± 0.02 ppt yr1 from October 1994 to March 1997, slightly larger than the growth rate calculated from our Oregon data of 1.5 pptv yr1 from 1994 to 1997. Montzka et al. (1996) reports a growth of approximately 100% yr1 from early 1994 to mid-1995 (global average), while our measurements of Oregon samples (mid-N hemisphere) indicates an increase of 113% yr1 from 1994 to 1995. In the same report, Montzka et al. (1996) estimated a mean growth rate of 0.80 ppt yr1 for samples collected between mid1993 and early 1995 at Niwot Ridge, Colorado. This agrees closely to our average growth rate in Oregon of 0.77 pptv yr1 from 1993 to 1995. For comparison with the present measurements, the Niwot Ridge data obtained by Montzka et al. (1996) is represented by the thin trend line in Fig. 4C, along with recent data from the AGAGE program at Mace Head. Because the production of CF3 CH2 F has increased very rapidly in the recent decade, a particularly large difference in its northern versus southern Hemispheric mixing ratios is expected if this compound has been produced primarily in the northern hemisphere. As shown in Fig. 5C, a particularly large hemispheric difference is, in fact, observed. In January 1997, the interhemispheric difference in the mixing ratio is about 2.2 pptv. 3.2. Source deconvolution The source deconvolution presented here sets a benchmark for the rare gases discussed in the previous sections of the paper. A comparison of three CF3 -compounds modeled elsewhere with the source estimates made here is intended to show the utility of the values shown in Table 2. With a simple one-box model, we estimated both the annual and five-year average

1116

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

Table 2 Average calculated emissions in Gg yr1 over five-year periods C3 F8

CF3 Cl

CF3 CF2 Cl

CF3 CFCl2

CF3 Br

CF3 H

CF3 CH3

CF3 CFH2

1977–1982 1982–1987 1987–1992 1992–1997

0.04 0.21 0.11 0.48

1.8 3.2 1.4 0.9

5.9 9.4 10.1 7.4

6.5 10.5 0.6 7.9

1.5 3.1 3.4 2.3

4.6 3.9 4.4 8.9

0.2 0.6 0.8 3.3

1.3 13.8

Lifetime (s) years

2600

640

1700

300

65

270

52

14

emissions of the eight gases from the time series of concentrations at Cape Meares, Oregon. The Oregon concentration was corrected to the global tropospheric average using the data from Alaska and Antarctica: CGlobal ¼ a  CCM  0:94; "  #, n X 1 CSi 1þ a¼ n; 2 CNi i¼1

ð1Þ

where a is the scale factor adjusting the Cape Meares time series to the global tropospheric average; 0.94 is an approximate conversion factor to adjust the tropospheric value to the atmospheric value; CSi is the annual average concentration at Palmer Station, Antarctica during year i, and CNi is the annual average of the measurements in Oregon and at Pt. Barrow, Alaska for year i, when i ¼ 1992 to 1997; and n is the number of years for which data exists in both the northern and southern hemispheres. The global average concentration (C) is inserted into Eq. (2) to solve for the global source (S): S¼

dC C þ ; dt s

Si ¼ ðCiþ1  Ci Þ þ

ð2Þ 1 Ci þ Ciþ1 ; 2 s

ð3Þ

where s is the average lifetime of the gas. Eq. (3) shows the calculation for the annual average source. The lifetimes used for the gases were from the recent World Meteorological Organization report (Montzka et al., 2003) with values ranging from s ¼ 14 yr (CF3 CH3 , HFC 143a) to s ¼ 2600 yr (C3 F8 , FC 218). The lifetime for CFC 114 (300 yr) was used for its isomer CFC 114a, though stratospheric measurements (Sturges et al., 2000) suggest that CFC 114a may have a shorter lifetime. All lifetimes used in the analysis are shown in Table 2, with the estimated source emissions of all gases by five-year average periods. The emissions from CF3 Br (H-1301), CF3 H (HFC 23) and CF3 CH2 F (HFC 134a) have been modeled carefully by other research groups. The histories of the gases are very different and are shown in Fig. 6

to demonstrate the range of sources. The estimated annual emissions for CF3 Br indicate a threefold increase from 1978 to 1986 to a maximum emission rate of about 4 Gg yr1 . From 1990 to 1997 emissions of CF3 Br decreased dramatically almost back to the 1980 level. Estimates for the annual release of CF3 Br by Butler et al. (1998) and Fraser et al. (1999) indicate the same general trend of emissions peaking in the late 1980s and then continuously decreasing. CF3 Br has been used primarily as a fire-extinguishing agent and, due to its very high ozone depletion potential, its production has been discontinued in developed countries, though it is still produced elsewhere (Fraser et al., 1999). Fig. 6A compares the estimated annual release of CF3 Br from this study with that of Butler et al. (1998). Fig. 6B compares the annual average estimates of the emission of CF3 H with the estimate by Oram et al. (1998). The source estimates from this study are far more variable than the calculations of Oram et al. This is probably partly due to the larger variability in the Cape Meares concentrations for CF3 H (discussed above) though smoothing the data by taking annual averages should reduce that effect, and also due to increased variability reflecting closer proximity to the source of the gas in the northern hemisphere. Our estimate may reflect the change in use of CF3 H from a raw material in the production of CF3 Br, declining rapidly when production of that gas ceased, then increasing again due to a variety of new sources, as described in Oram et al. (1998). The Cape Meares data show extreme changes in slope at approximately the same time periods as the more moderate slope changes modeled by Oram et al. from measurements in the southern hemisphere. CF3 CH2 F is a relatively new CFC-replacement compound, and continues to increase in the atmosphere. Fig. 6C compares the estimated emissions of CF3 CH2 F from this study with Oram et al. (1996) and McCulloch et al. (2003). While all studies show the same general characteristics, the simple one-box model used here may over estimate the early emissions of HFC 134a due to the global averaging of transport. Differences in calibration and emphasis on northern vs. southern hemisphere measurements for the early years

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

1117

taining compounds, mostly from the northern hemisphere. The historic data reflect the expected changes in the respective trace gas emissions, and the annual averages are archived here for comparison and further analysis. The emissions calculated in this study agree generally with the large features of the source emissions from other studies. The five-year average emissions archived here for the rarer gases should also give a first estimate of their emissions, probably more representative of features in the northern hemisphere.

Acknowledgements This research was supported by a grant from the NASA/EPSCoR program (grant NCCW-0058) to Montana State University. Data for NOAA CMDL is made available at www.cmdl.noaa.gov, and used by permission. Data for the AGAGE program and Oram et al. (1998) is archived at the US DOE Carbon Dioxide Information Analysis Center (CDIAC), at www.cdiac. esd.ornl.gov. This work was done as an exploratory part of the research on the perfluorocarbons CF4 and C2 F6 , which was funded in part by a grant from the International Aluminum Institute (IAI) to Andarz Co. We thank Mr. Mark Tarver of IPAI (later IAI), Jerry Marks (consultant) and Bud Lieber (Kaiser Aluminum). Additional support was provided by Biospherics Research Corporation.

References Fig. 6. Comparison of estimates of annual source emissions ( ) in Gg yr1 for (A) CF3 Br, compared to source estimates (M) from Butler et al. (1998); (B) CF3 H, compared to sources estimates (M) from Oram et al. (1998); and (C) CF3 CH2 F, compared to source estimates (M) from Oram et al. (1996) and ( ) from McCulloch et al. (2003).



may also lead to a difference in the emission estimates between the studies. However, the overall features are similar for all estimates. Our estimates for annual emissions of CF3 CH2 F in Fig. 6C indicate rapid increases in the 1990s leading to an emission rate of 14 Gg yr1 by 1995.

4. Conclusions HRGC–HRMS was used successfully to measure a unique time series of concentrations of rare CF3 -con-

Butler, J.H., Elkins, J.W., Hall, B.D., Cummings, S.O., Montzka, S.A., 1992. A decrease in the growth rates of atmospheric halon concentrations. Nature 359, 403– 405. Butler, J.H., Montzka, S.A., Clarke, A.D., Lobert, J.M., Elkins, J.W., 1998. Growth and distribution of halons in the atmosphere. J. Geophys. Res. 103, 1503–1511. Culbertson, J.A., Prins, J.M., Grimsrud, E.P., 2000. Improvements in the detection and analysis of CF3 -containing compounds in the background atmosphere by gas chromatography/high resolution mass spectrometry. J. Chromatogr. A 903, 261–265. Daniel, J.S., Solomon, S., Albritton, D.L., 1995. On the evaluation of halocarbon radiative forcing and global warming potentials. J. Geophys. Res. 100, 1271–1285. Daniel, J.S., Schauffler, S.M., Plock, W.H., Solomon, S., Weaver, A., Heidt, L.E., Garcia, R.R., Atlas, E.L., Vedder, J.F., 1996. On the age of stratospheric air and inorganic chlorine and bromine release. J. Geophys. Res. 101, 16757– 16770. Engen, M.A., Wagner, V.A., Sears, L.J., Grimsrud, E.P., 1998. Detection of CF3 -containing compounds in background air

1118

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119

by gas chromatography/high-resolution mass spectrometry. J. Geophys. Res. 103, 25287–25297. Engen, M.A., Culbertson, J.A., Grimsrud, E.P., 1999. Analysis of brominated compounds in background air by gas chromatography–high-resolution mass spectrometry. J. Chromatogr. 848, 261–277. Fabian, P., Borchers, R., Leifer, R., Subbaraya, B.H., Lal, S., Boy, M., 1996. Global stratospheric distribution of halocarbons. Atmos. Environ. 30, 1787–1796. Fisher, D.A., Hales, C.H., Filkin, D.L., Ko, M.K.W., Dak Sze, N., Connell, P.S., Wuebbles, D.J., Isaksen, I.S.A., Stordal, F., 1990a. Model calculations of the relative effects of CFCs and their replacements on stratospheric ozone. Nature 344, 508–512. Fisher, D.A., Hales, C.H., Wang, W., Ko, M.K.W., Dak Sze, N., 1990b. Model calculations of the relative effects of CFCs and their replacements on global warming. Nature 344, 513–516. Fraser, P.J., Oram, D.E., Reeves, C.E., Penkett, S.A., McCulloch, A., 1999. Southern hemispheric halon trends (1978– 1998) and global halon emissions. J. Geophys. Res. 104, 15985–15999. Gunawardena, R., 1989. Global distribution of organo-bromine gases. Ph.D. Dissertation, Oregon Graduate Center, Beaverton, OR, USA. Hayman, G.D., Derwent, R.G., 1997. Atmospheric chemical reactivity and ozone-forming potentials of potential CFC replacements. Environ. Sci. Technol. 31, 327–336. Khalil, M.A.K., Rasmussen, R.A., 1985. The trend of bromochlorodifluoromethane and the concentrations of other bromine-containing gases at the South Pole. Antarct. J. US 20, 206–207. Khalil, M.A.K., Rasmussen, R.A., Culbertson, J.A., Prins, J.M., Grimsrud, E.P., Shearer, M.J., 2003. Atmospheric perfluorocarbons. Environ. Sci. Technol. 37, 4358–4361. McCulloch, A., Midgley, P.M., Ashford, P., 2003. Releases of refrigerant gases (CFC-12, HCFC-22 and HFC-134a) to the atmosphere. Atmos. Environ. 37, 889–902. McElroy, M.B., Salawitch, R.J., 1989. Changing composition of the global stratosphere. Science 243, 763–770. Molina, M.J., Rowland, F.S., 1974. Stratospheric sink for chlorfluoromethanes: chlorine atom-catalyzed destruction of ozone. Nature 249, 810–812. Montzka, S.A., Myers, R.C., Butler, J.H., Elkins, J.W., 1996. Observations of HFC-134a in the remote troposphere. Geophys. Res. Lett. 23, 169–172. Montzka, S.A., Butler, J.H., Elkins, J.W., Thompson, T.M., Clarke, A.D., Lock, L.T., 1999. Present and future trends in the atmospheric burden of ozone-depleting halogens. Nature 398, 690–694. Montzka, S.A., Fraser, P.J., et al., 2003. Controlled substances and other source gases. In: Scientific Assessment of Ozone Depletion: 2002. World Meteorological Organization, Geneva, Switzerland, pp. 1.1–1.87 (Chapter 1). NASA (1994). NASA Reference Publication 1339. In: Kaye, J.A., Penkett, S.A., Ormond, F.M. (Eds.), Report on Concentrations, Lifetimes, and Trends of CFCs, Halons, and Related Species. Washington, DC. Oram, D.E., Reeves, C.E., Strurges, W.T., Penkett, S.A., 1996. Recent tropospheric growth rate and distribution of HFC-134a (CF3 CH2 F). Geophys. Res. Lett. 23, 1949–1952.

Oram, D.E., Sturges, W.T., Penkett, S.A., McCulloch, A., Fraser, P.J., 1998. Growth of fluoroform (CHF3 , HFC-23) in the background atmosphere. Geophys. Res. Lett. 25, 35– 38. Penkett, S.A., Prosser, N.J.D., Rasmussen, R.A., Khalil, M.A.K., 1981. Atmospheric measurements of CF4 and other fluorocarbons containing the CF3 grouping. J. Geophys. Res. 86, 5172–5178. Peters, D.G., Hayes, J.M., Hieftje, G.M., 1974. Chemical Separations and Measurements. W.B. Saunders Company, Philadelphia. p. 14. Pollock, W.H., Heidt, L.E., Lueb, R.A., Vedder, J.F., Mills, M.J., Solomon, S., 1992. On the age of stratospheric air and ozone depletion potentials in polar regions. J. Geophys. Res. 97, 12993–12999. Prather, M.J., Watson, R.T., 1990. Stratospheric ozone depletion and future levels of atmospheric chlorine and bromine. Nature 344, 729–734. Prinn, R.G., Weiss, R.F., Fraser, P.J., Simmonds, P.G., Cunnold, D.M., Alyea, F.N., O’Doherty, S., Salameh, P., Miller, B.R., Huang, J., Wang, R.H.J., Hartley, D.E., Harth, C., Steele, L.P., Sturrock, G., Midgely, P.M., McCulloch, A., 2000. A history of chemically and radiatively important gases in air deduced from ALE/GAGE/ AGAGE. J. Geophys. Res. 115, 17751– 17792. Pruette, L., Karecki, S., Reif, R., Tousignanat, L., Reagan, W., Kesari, S., Zazzera, L., 1999. Environmental issues in the electronics and semiconductor industries. Electrochem. Soc. 99 (8), 20–29. Rasmussen, R.A., Khalil, M.A.K., 1980. Atmospheric halocarbons: Measurements and analyses of selected trace gases. In: Proc. NATO Adv. Study Inst. FAA-EE-80-20, pp. 209–232. Ravishankara, A.R., Solomon, S., Turnipseed, A.A., Warren, R.F., 1993. Atmospheric lifetimes of long-lived halogenated species. Science 259, 194–199. Schauffler, S.M., Heidt, L.E., Pollock, W.H., Gilpin, T.M., Vedder, J.F., Solomon, S., Lueb, R.A., Atlas, E.L., 1993. Measurements of halogenated organic compounds near the tropical tropopause. Geophys. Res. Lett. 20, 2567– 2570. Schauffler, S.M., Atlas, E.L., Blake, D.R., Flocke, F., Lueb, R.A., Lee-Taylor, J.M., Stroud, V., Travnicek, W., 1999. Distributions of brominated organic compounds in the troposphere and lower stratosphere. J. Geophys. Res. 104, 21513–21535. Schneider, S.H., 1989. The greenhouse effect: science and policy. Science 243, 171–181. Simmonds, P.G., O’Doherty, S., Huang, J., Derwent, R.G., Ryall, D., Nickless, G., Cunnold, D., 1998. Calculated trends and the atmospheric abundance of 1,1,1,2-tetrafluoroethane, 1,1-dichloro-1-fluoroethane, and 1-chloro-1, 1-difluoroethane using automated in-situ gas chromatography–mass spectrometry measurements recorded at Mace Head, Ireland, from October 1994 to March 1997. J. Geophys. Res. 103, 16029–16037. Singh, O.N., Borchers, R., Fabian, P., Lal, S., Subbaraya, B.H., 1988. Measurements of stratospheric bromine. Nature 334, 539–542. Solomon, S., Mills, M., Heidt, L.E., Pollock, W.H., Tuck, A.F., 1992. On the evaluation of ozone depletion potentials. J. Geophys. Res. 97, 825–842.

J.A. Culbertson et al. / Chemosphere 55 (2004) 1109–1119 Sturges, W.T., Oram, D.E., Penkett, S.A., Fraser, P.J., Engel, A., 2000. Long-lived halogenated compounds in the stratosphere. In: van Ham, J. et al. (Eds.), Non-CO2 Greenhouse Gases: Scientific Understanding, Control, and Implementation. Kluwer Academic Publishers, The Netherlands, pp. 239–240.

1119

Sturrock, G.A., Porter, L.W., Fraser, P.J., 2001. In situ measurement of CFC replacement chemicals and other halocarbons at Cape Grim: the AGAGE GC-MS program. Baseline Atmosphere Program (Australia) 1997–1998, pp. 43–49.