Atmospheric measurements of HCFC-22 at the South Pole
other support was provided by the Biospherics Research Corporation and the Andarz Company.
dramatically during recent years because of legislative controls, enacted because CO is regarded as a highly undesirable pollutant that leads to adverse health effects and urban pollution (EPA 1990; Khalil and Rasmussen 1990). Reactive hydrocarbons that can lead to the atmospheric formation of CO are also controlled. The other process, increase of OH, which causes a greater removal of CO thus leading to declining concentrations, can occur because of possible reduction of stratospheric ozone that allows more ultraviolet radiation to reach the troposphere where it stimulates the production of OH (Madronich and Granier 1992). The possibility that OH is increasing in recent years is a reversal of earlier concerns that it may be depleted by human activities. At present, there is no direct or indirect experimental evidence for changes in OH. We thank the National Oceanic and Atmospheric Administration Climate Modeling and Diagnostics Laboratory program for collecting samples at South Pole Station and Palmer Station; P.J. Fraser and the Commonwealth Scientific and Industrial Research Organization staff for collecting samples at Cape Grim, Tasmania; D. Stearns and R. Dalluge for laboratory and fieldwork; and J. Mohan and M.J. Shearer for data management. Financial support for recent work was provided in part by National Science Foundation grant OPP 87-17023;
References Environmental Protection Agency. 1990. Air quality criterion for carbon monoxide (document number EPAI600/8-901045A). Research Triangle Park, North Carolina: U.S. EPA. Fraser, P.1., P. Hyson, R.A. Rasmussen, A.J. Crawford, and M.A. K. Khalil. 1986. Methane, carbon monoxide, and methyichioroform in the southern hemisphere. Journal
of Atmospheric Chemistry, 4,
3-42. Khalil, M.A.K., and R.A. Rasmussen. 1985. Variability of methane and carbon monoxide at the South Pole. Antarctic Journal of the U.S., 19(5), 204-206. Khalil, M.A.K., and R.A. Rasmussen. 1988. Carbon monoxide in the Earth's atmosphere: Indications of a global increase. Nature, 332, 242-245. Khalil, M.A.K., and R.A. Rasmussen. 1990. Global cycle of CO—Trends and mass balance. Chemosphere, 20, 227-242. Madronich, S., and C. Granier. 1992. Impact of recent total ozone changes on tropospheric ozone photodissociation, hydroxyl radicals, and methane trends. Geophysical Research Letters, 19, 465-467. Thompson, A.M. 1992. The oxidizing capacity of the Earth's atmosphere: Probable past and future changes. Science, 286, 1157-1165.
Atmospheric measurements of HCFC-22 at the South Pole S.A. MONTzKA, R.C. MYERS, J.H. BUTLER, and J.W. ELKINS, Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80303 S.O. CUMMINGS, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309
agent for open- and closed-cell foams (Midgley and Fisher 1993). We have measured HCFC-22 in air samples collected at seven remote stations around the globe since the end of 1991. In the Southern Hemisphere, samples are collected at three different remote locations: Amundsen-Scott South Pole Station, at the South Pole (90°S); Cape Grim Baseline Air Pollution Station, Australia (40.7°S 144.8°E); and Cape Matatula, American Samoa (14.3°S 170.6°W). Here, we report measurements made at the South Pole through the end of 1992 and discuss them in light of results obtained at the next nearest station, Cape Grim. Paired samples of air were collected monthly in 0.85-liter (L) electropolished stainless-steel flasks. Flasks were filled to a maximum pressure [approximately 25 pounds per square inch, gauge (psig) for South Pole samples and approximately 40 psig for Cape Grim samples] without drying agents in line. Samples were analyzed by capillary gas chromatography with mass spectrometric detection. Detailed procedures for collection and analysis of air for HCFCs are described elsewhere (Montzka et al. 1992, 1993, in press). Data are not reported for
oncern for stratospheric ozone depletion in polar regions C and around the globe has prompted many nations to agree to phase out production and use of fully halogenated chlorofluorocarbons (CFCs) over the next few years (UNEP 1987). Because of this action, the atmospheric growth rates of CFCs and bromine-containing halons have declined in recent years (Butler et al. 1992; Elkins et al. 1993). Partially hydrogenated chlorofluorocarbons, also known as hydrochlorofluorocarbons (HCFCs), are among the different classes of compounds used as replacements for CFCs. HCFCs are preferred to CFCs because model calculations predict that HCFCs will have shorter atmospheric lifetimes and release less reactive chlorine to the stratosphere. The HCFCs are viewed only as interim replacements for CFCs, however, because they still have some potential to destroy ozone. Ozone-depletion potentials of HCFCs are generally predicted to be less than 15 percent, by weight, of those for the CFCs that they will replace (Solomon et al. 1992). The major HCFC in use today is HCFC-22 (CHC1F 2). This compound is used primarily for refrigeration and air-conditioning applications and, to a lesser extent, as a blowing
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100
age time on compounds collected in flasks. The mean mixing ratio of HCFC-22 at both sites during 1992 was 95 ppt (figure 1). Similar mixing ratios (within a few percent) for trace gases at both the South Pole and Cape Grim are expected for compounds that have lifetimes that are long with respect to interhemispheric meridional transport and if most emission to the atmosphere occurs in the Northern Hemisphere. Similar mixing ratios at these two sites are observed for compounds such as methane, CFC-11, and CFC-12 (Steele et al. 1987; Elkins et al. 1993). For HCFC-22, one would expect similar mixing ratios at both sites and observations show this to be true (figure 1). Air collected at the South Pole, however, is considerably drier than from Cape Grim. Mean yearly dewpoint temperatures are less than -50°C at the South Pole and are 10°C at Cape Grim. In extremely dry samples, certain compounds such as carbon tetrachloride (Cd 4) are susceptible to losses within our sample flasks. It has also been suggested that HCFC-22 is unstable in certain air sampling containers (Fraser et al. in press). The agreement between results from the two sampling locations, however, suggests that HCFC-22 is stable in these flasks under a wide range of water-mixing ratios. Furthermore, the variability of HCFC-22 from individual flasks is not correlated with the loss of CC1 4 in these flasks (figure 2). These results suggest that, within flask samples that are dry enough for losses of Cd 4 to occur, no significant losses are observed for HCFC-22. The stability of compounds within flask containers can also be studied by monitoring the mixing ratios of compounds within these containers over time. By assuming a linear growth rate of HCFC-22 in the atmosphere at the South Pole and Cape Grim, one can study the measured mixing ratio for HCFC-22 as a function of time elapsed between sampling and analysis (figure 3). No significant trend can be found for the data plotted in this figure, suggesting that HCFC-22 is stable in these flasks for extended periods.
• S.Pole + C.Grh
98 .97 0 ,.296 05 CsJ a94 LL593 192 91 90 i•. 1992
1992.5
1993
Collection Date Figure 1. Mixing ratio of HCFC-22 at the South Pole and Cape Grim as determined from flask sample pairs in 1991 and 1992. The line drawn is a linear fit to the data from Cape Grim. all months of 1992 because of problems encountered, including flask unavailability, leaks, or local contamination (Montzka et al. 1993). Because of the nature of shipping to and from the South Pole, samples are collected and stored in flasks throughout the austral winter and then sent to Boulder for analysis in December and January. The mean number of days elapsed between collection and analysis for samples collected at the South Pole was 94 days. Flasks collected at other stations, including Cape Grim, are sent to Boulder as soon as possible after collection. The mean delay between collection and analysis for flask collected at Cape Grim was 36 days. Measurements of HCFC-22 have been obtained from air collected at the South Pole since the latter part of 1991 (figure 1). The mean mixing ratio of HCFC-22 at the South Pole in 1992 was estimated at 95 parts per trillion (ppt) from the midyear value, as predicted from a linear fit of the available data. This average is 25-30 percent less than had been predicted from previously reported ground-based measurements of HCFC-22 at this site (Rasmussen and Khalil 1983). These differences are most likely due to differences in calibration gas standards (Montzka et al. 1993). The measurements reported here are based on the National Oceanic and Atmospheric Administration's (NOAA's) Climate Modeling and Diagnostics Laboratory (NOAA-CMDL) calibration gas standards. Flask-based measurements referenced to these standards yield results that are in good agreement with long-path absorption measurements in similar latitude bands (Rinsland et al. 1989; Zander et al. 1992) and model calculations with current emission estimates (Midgley and Fisher 1993). The growth rate of atmospheric HCFC-22 during 1992 at the South Pole is identical to the rate observed at Cape Grim and is 5.3 ppt per year (figure 1). This rate is also consistent with a previous estimate for the Southern Hemisphere during 1992 of 5.0 (±1.6) ppt per year (Montzka et al. 1993). This latter rate was estimated from the mean interhemispheric difference observed during 1992 and a simple model (Butler et al. 1992). Samples collected at both the South Pole and Cape Grim offer an opportunity to study the effects of humidity and stor-
. 0 C ci) co 2 c E o 4: CNI -1 go I LL V o -3 .I cc -5 0% 20% 40% 60% 80% 100%
Loss of Carbon Tetrachloride Figure 2. Variability in measurements of HCFC-22 related to in-flask losses of CCI4. The residuals were obtained from a linear fit to the individual flask results for HCFC-22 from the South Pole. Losses of Cd 4 were calculated by comparing the measured mixing ratio of CCI4 from South Pole flasks to the yearly average CCI 4 mixing ratio at Cape Grim.
ANTARCTIC JOURNAL - REVIEW 1993
268
/
Ed
CL
++
c 1_ +
_J. •1-' •
Cd C/)
E .c +
+
+
S
++
S
•
U----
+
SouI Pole
-2
+ Cape Grim
.3-.I 0 0 50 100 150 200
Days Elapsed Between Collection and Analysis Figure 3. The effect of sample storage on mixing ratios of HCFC-22 in flasks from the South Pole and Cape Grim. The plotted residuals were obtained from a linear fit to the data at each station. A mean atmospheric mixing ratio of 95 ppt was determined for HCFC-22 during 1992 at the South Pole. Similar mixing ratios were observed at the South Pole and Cape Grim, suggesting that the mixing ratio of HCFC-22 is fairly constant in the Southern Hemisphere below 40 0 S. Finally, comparisons between results from the South Pole and Cape Grim suggest that HCFC-22 is stable in both dry and wet flask samples for extended periods. We thank the National Science Foundation and B. Mendonca for logistical support, and we thank personnel involved with flask sampling at both the South Pole and Cape Grim. This work was supported in part by the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program.
trations. Nature, 359(6394), 403-405. Elkins, J.W., T.M. Thompson, T.H. Swanson, J.H. Butler, B.D. Hall, S.O. Cummings, D.A. Fisher, and A.G. Raffo. 1993. Decrease in the growth rates of atmospheric chlorofluorocarbons 11 and 12. Nature, 364(6440), 780-783. Fraser, P.J., S. Penkett, M. Gunson, R. Weiss, and F.S. Rowland. In press. NASA report on concentrations, lifetimes, and trends of CFCs, halons and related species. Washington, D.C.: U.S. Government Printing Office. Midgley, P.M. and D.A. Fisher. 1993. The production and release to the atmosphere of chlorodifluoromethane (HCFC-22). Atmospheric Environment, 27A(14), 2215-2223. Montzka, S.A., J.W. Elkins, J.H. Butler, T.M. Thompson, W.T. Sturges, T.H. Swanson, R.C. Myers, T.M. Gilpin, T.J. Baring, S.O. Cummings, G.A. Holcomb, J.M. Lobert, and B.D. Hall. 1992. Nitrous oxide and halocarbons division (chapter 5). In E.E. Ferguson and R. Rossen (Eds.), Summary report 1991: Climate Monitoring and Diagnostic Laboratory (Vol. 20). Boulder, Colorado: NOAA Climate Monitoring and Diagnostics Laboratory. Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, and S.O. Cummings. 1993. Global tropospheric distribution and calibration scale of HCFC-22. Geophysical Research Letters, 20(8), 703-706. Montzka, S.A., M.R. Nowick, R.C. Myers, J.W. Elkins, J.H. Butler, S.O. Cummings, P.J. Fraser, and L.W. Porter. In press. NOAA/CMDL chlorodifluoromethane (HCFC-22) observations at Cape Grim.
Baseline 91. Rasmussen, R.A., and M.A.K. Khalil. 1983. Rare trace gases at the South Pole. Antarctic Journal of the U.S., 18(5), 250-252. Rinsland, C.P., D.W. Johnson, A. Goldman, and J.S. Levine. 1989. Evidence for a decline in the atmospheric accumulation rate of CHC1F2 (CFC-22). Nature, 337(6207), 535-537. Solomon, S., M. Mills, L.E. Heidt, W.H. Pollock, and A.F. Tuck. 1992. On the evaluation of ozone depletion potentials. Journal of Geophysical Research, 97(D1), 825-842. Steele, L.P., P.J. Fraser, R.A. Rasmussen, M.A.K. Khalil, T.J. Conway, A.J. Crawford, R.H. Gammon, K.A. Masarie, and K.W. Thoning. 1987. The global distribution of methane in the troposphere. Journal ofAtmospheric Chemistry, 5(2), 125-171. UNEP (United Nations Environmental Program). 1987. Montreal protocol to reduce substances that deplete the ozone layer report (final report). New York: UNEP. Zander, R., M.R. Gunson, C.B. Farmer, C.P. Rinsland, F.W. Irion, and E. Mahieu. 1992. The 1985 chlorine and fluorine inventories in the stratosphere based on ATMOS observations at 30 0 north latitude. Journal ofAtmospheric Chemistry, 15(2), 171-186.
References Butler, J.H., J.W. Elkins, B.D. Hall, S.O. Cummings, and S.A. Montzka. 1992. A decrease in the growth rates of atmospheric halon concen-
Atmospheric longwave radiation spectrum and near-surface atmospheric temperature profiles at South Pole Station VON P. WALDEN and STEPHEN
G. WARREN, Geophysics Program, University of Washington, Seattle, Washington 98195
radiation spectrum coincident with the state of the atmosphere for use in our climate studies at the University of Washington. The data set spans the full year from 14 January 1992 through 14 January 1993. We are attempting to determine the controls of the longwave radiation budget on the antarctic plateau and to offer spectral measurements for use in testing atmospheric radiation models and radiation codes in climate models.
he antarctic atmosphere is the coldest and driest on T Earth. The downward clear-sky emission to the ice sheet in winter averages about 75 watts per square meter, that is, less than half that for the subarctic winter standard atmosphere (figure 1 and the table). In a collaborative effort at South Pole Station with Frank J. Murcray and Renate Heuberger of the University of Denver, we have compiled a data set of surface-based measurements of the downward
ANTARCTIC JOURNAL - REVIEW 1993
269
dramatically during recent years because of legislative controls, enacted because CO is regarded as a highly undesirable pollutant that leads to adverse health effects and urban pollution (EPA 1990; Khalil and Rasmussen 1990). Reactive hydrocarbons that can lead to the atmospheric formation of CO are also controlled. The other process, increase of OH, which causes a greater removal of CO thus leading to declining concentrations, can occur because of possible reduction of stratospheric ozone that allows more ultraviolet radiation to reach the troposphere where it stimulates the production of OH (Madronich and Granier 1992). The possibility that OH is increasing in recent years is a reversal of earlier concerns that it may be depleted by human activities. At present, there is no direct or indirect experimental evidence for changes in OH. We thank the National Oceanic and Atmospheric Administration Climate Modeling and Diagnostics Laboratory program for collecting samples at South Pole Station and Palmer Station; P.J. Fraser and the Commonwealth Scientific and Industrial Research Organization staff for collecting samples at Cape Grim, Tasmania; D. Stearns and R. Dalluge for laboratory and fieldwork; and J. Mohan and M.J. Shearer for data management. Financial support for recent work was provided in part by National Science Foundation grant OPP 87-17023;
References Environmental Protection Agency. 1990. Air quality criterion for carbon monoxide (document number EPAI600/8-901045A). Research Triangle Park, North Carolina: U.S. EPA. Fraser, P.1., P. Hyson, R.A. Rasmussen, A.J. Crawford, and M.A. K. Khalil. 1986. Methane, carbon monoxide, and methyichioroform in the southern hemisphere. Journal
of Atmospheric Chemistry, 4,
3-42. Khalil, M.A.K., and R.A. Rasmussen. 1985. Variability of methane and carbon monoxide at the South Pole. Antarctic Journal of the U.S., 19(5), 204-206. Khalil, M.A.K., and R.A. Rasmussen. 1988. Carbon monoxide in the Earth's atmosphere: Indications of a global increase. Nature, 332, 242-245. Khalil, M.A.K., and R.A. Rasmussen. 1990. Global cycle of CO—Trends and mass balance. Chemosphere, 20, 227-242. Madronich, S., and C. Granier. 1992. Impact of recent total ozone changes on tropospheric ozone photodissociation, hydroxyl radicals, and methane trends. Geophysical Research Letters, 19, 465-467. Thompson, A.M. 1992. The oxidizing capacity of the Earth's atmosphere: Probable past and future changes. Science, 286, 1157-1165.
Atmospheric measurements of HCFC-22 at the South Pole S.A. MONTzKA, R.C. MYERS, J.H. BUTLER, and J.W. ELKINS, Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80303 S.O. CUMMINGS, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309
agent for open- and closed-cell foams (Midgley and Fisher 1993). We have measured HCFC-22 in air samples collected at seven remote stations around the globe since the end of 1991. In the Southern Hemisphere, samples are collected at three different remote locations: Amundsen-Scott South Pole Station, at the South Pole (90°S); Cape Grim Baseline Air Pollution Station, Australia (40.7°S 144.8°E); and Cape Matatula, American Samoa (14.3°S 170.6°W). Here, we report measurements made at the South Pole through the end of 1992 and discuss them in light of results obtained at the next nearest station, Cape Grim. Paired samples of air were collected monthly in 0.85-liter (L) electropolished stainless-steel flasks. Flasks were filled to a maximum pressure [approximately 25 pounds per square inch, gauge (psig) for South Pole samples and approximately 40 psig for Cape Grim samples] without drying agents in line. Samples were analyzed by capillary gas chromatography with mass spectrometric detection. Detailed procedures for collection and analysis of air for HCFCs are described elsewhere (Montzka et al. 1992, 1993, in press). Data are not reported for
oncern for stratospheric ozone depletion in polar regions C and around the globe has prompted many nations to agree to phase out production and use of fully halogenated chlorofluorocarbons (CFCs) over the next few years (UNEP 1987). Because of this action, the atmospheric growth rates of CFCs and bromine-containing halons have declined in recent years (Butler et al. 1992; Elkins et al. 1993). Partially hydrogenated chlorofluorocarbons, also known as hydrochlorofluorocarbons (HCFCs), are among the different classes of compounds used as replacements for CFCs. HCFCs are preferred to CFCs because model calculations predict that HCFCs will have shorter atmospheric lifetimes and release less reactive chlorine to the stratosphere. The HCFCs are viewed only as interim replacements for CFCs, however, because they still have some potential to destroy ozone. Ozone-depletion potentials of HCFCs are generally predicted to be less than 15 percent, by weight, of those for the CFCs that they will replace (Solomon et al. 1992). The major HCFC in use today is HCFC-22 (CHC1F 2). This compound is used primarily for refrigeration and air-conditioning applications and, to a lesser extent, as a blowing
ANTARCTIC JOURNAL - REVIEW 1993
267
100
age time on compounds collected in flasks. The mean mixing ratio of HCFC-22 at both sites during 1992 was 95 ppt (figure 1). Similar mixing ratios (within a few percent) for trace gases at both the South Pole and Cape Grim are expected for compounds that have lifetimes that are long with respect to interhemispheric meridional transport and if most emission to the atmosphere occurs in the Northern Hemisphere. Similar mixing ratios at these two sites are observed for compounds such as methane, CFC-11, and CFC-12 (Steele et al. 1987; Elkins et al. 1993). For HCFC-22, one would expect similar mixing ratios at both sites and observations show this to be true (figure 1). Air collected at the South Pole, however, is considerably drier than from Cape Grim. Mean yearly dewpoint temperatures are less than -50°C at the South Pole and are 10°C at Cape Grim. In extremely dry samples, certain compounds such as carbon tetrachloride (Cd 4) are susceptible to losses within our sample flasks. It has also been suggested that HCFC-22 is unstable in certain air sampling containers (Fraser et al. in press). The agreement between results from the two sampling locations, however, suggests that HCFC-22 is stable in these flasks under a wide range of water-mixing ratios. Furthermore, the variability of HCFC-22 from individual flasks is not correlated with the loss of CC1 4 in these flasks (figure 2). These results suggest that, within flask samples that are dry enough for losses of Cd 4 to occur, no significant losses are observed for HCFC-22. The stability of compounds within flask containers can also be studied by monitoring the mixing ratios of compounds within these containers over time. By assuming a linear growth rate of HCFC-22 in the atmosphere at the South Pole and Cape Grim, one can study the measured mixing ratio for HCFC-22 as a function of time elapsed between sampling and analysis (figure 3). No significant trend can be found for the data plotted in this figure, suggesting that HCFC-22 is stable in these flasks for extended periods.
• S.Pole + C.Grh
98 .97 0 ,.296 05 CsJ a94 LL593 192 91 90 i•. 1992
1992.5
1993
Collection Date Figure 1. Mixing ratio of HCFC-22 at the South Pole and Cape Grim as determined from flask sample pairs in 1991 and 1992. The line drawn is a linear fit to the data from Cape Grim. all months of 1992 because of problems encountered, including flask unavailability, leaks, or local contamination (Montzka et al. 1993). Because of the nature of shipping to and from the South Pole, samples are collected and stored in flasks throughout the austral winter and then sent to Boulder for analysis in December and January. The mean number of days elapsed between collection and analysis for samples collected at the South Pole was 94 days. Flasks collected at other stations, including Cape Grim, are sent to Boulder as soon as possible after collection. The mean delay between collection and analysis for flask collected at Cape Grim was 36 days. Measurements of HCFC-22 have been obtained from air collected at the South Pole since the latter part of 1991 (figure 1). The mean mixing ratio of HCFC-22 at the South Pole in 1992 was estimated at 95 parts per trillion (ppt) from the midyear value, as predicted from a linear fit of the available data. This average is 25-30 percent less than had been predicted from previously reported ground-based measurements of HCFC-22 at this site (Rasmussen and Khalil 1983). These differences are most likely due to differences in calibration gas standards (Montzka et al. 1993). The measurements reported here are based on the National Oceanic and Atmospheric Administration's (NOAA's) Climate Modeling and Diagnostics Laboratory (NOAA-CMDL) calibration gas standards. Flask-based measurements referenced to these standards yield results that are in good agreement with long-path absorption measurements in similar latitude bands (Rinsland et al. 1989; Zander et al. 1992) and model calculations with current emission estimates (Midgley and Fisher 1993). The growth rate of atmospheric HCFC-22 during 1992 at the South Pole is identical to the rate observed at Cape Grim and is 5.3 ppt per year (figure 1). This rate is also consistent with a previous estimate for the Southern Hemisphere during 1992 of 5.0 (±1.6) ppt per year (Montzka et al. 1993). This latter rate was estimated from the mean interhemispheric difference observed during 1992 and a simple model (Butler et al. 1992). Samples collected at both the South Pole and Cape Grim offer an opportunity to study the effects of humidity and stor-
. 0 C ci) co 2 c E o 4: CNI -1 go I LL V o -3 .I cc -5 0% 20% 40% 60% 80% 100%
Loss of Carbon Tetrachloride Figure 2. Variability in measurements of HCFC-22 related to in-flask losses of CCI4. The residuals were obtained from a linear fit to the individual flask results for HCFC-22 from the South Pole. Losses of Cd 4 were calculated by comparing the measured mixing ratio of CCI4 from South Pole flasks to the yearly average CCI 4 mixing ratio at Cape Grim.
ANTARCTIC JOURNAL - REVIEW 1993
268
/
Ed
CL
++
c 1_ +
_J. •1-' •
Cd C/)
E .c +
+
+
S
++
S
•
U----
+
SouI Pole
-2
+ Cape Grim
.3-.I 0 0 50 100 150 200
Days Elapsed Between Collection and Analysis Figure 3. The effect of sample storage on mixing ratios of HCFC-22 in flasks from the South Pole and Cape Grim. The plotted residuals were obtained from a linear fit to the data at each station. A mean atmospheric mixing ratio of 95 ppt was determined for HCFC-22 during 1992 at the South Pole. Similar mixing ratios were observed at the South Pole and Cape Grim, suggesting that the mixing ratio of HCFC-22 is fairly constant in the Southern Hemisphere below 40 0 S. Finally, comparisons between results from the South Pole and Cape Grim suggest that HCFC-22 is stable in both dry and wet flask samples for extended periods. We thank the National Science Foundation and B. Mendonca for logistical support, and we thank personnel involved with flask sampling at both the South Pole and Cape Grim. This work was supported in part by the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program.
trations. Nature, 359(6394), 403-405. Elkins, J.W., T.M. Thompson, T.H. Swanson, J.H. Butler, B.D. Hall, S.O. Cummings, D.A. Fisher, and A.G. Raffo. 1993. Decrease in the growth rates of atmospheric chlorofluorocarbons 11 and 12. Nature, 364(6440), 780-783. Fraser, P.J., S. Penkett, M. Gunson, R. Weiss, and F.S. Rowland. In press. NASA report on concentrations, lifetimes, and trends of CFCs, halons and related species. Washington, D.C.: U.S. Government Printing Office. Midgley, P.M. and D.A. Fisher. 1993. The production and release to the atmosphere of chlorodifluoromethane (HCFC-22). Atmospheric Environment, 27A(14), 2215-2223. Montzka, S.A., J.W. Elkins, J.H. Butler, T.M. Thompson, W.T. Sturges, T.H. Swanson, R.C. Myers, T.M. Gilpin, T.J. Baring, S.O. Cummings, G.A. Holcomb, J.M. Lobert, and B.D. Hall. 1992. Nitrous oxide and halocarbons division (chapter 5). In E.E. Ferguson and R. Rossen (Eds.), Summary report 1991: Climate Monitoring and Diagnostic Laboratory (Vol. 20). Boulder, Colorado: NOAA Climate Monitoring and Diagnostics Laboratory. Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, and S.O. Cummings. 1993. Global tropospheric distribution and calibration scale of HCFC-22. Geophysical Research Letters, 20(8), 703-706. Montzka, S.A., M.R. Nowick, R.C. Myers, J.W. Elkins, J.H. Butler, S.O. Cummings, P.J. Fraser, and L.W. Porter. In press. NOAA/CMDL chlorodifluoromethane (HCFC-22) observations at Cape Grim.
Baseline 91. Rasmussen, R.A., and M.A.K. Khalil. 1983. Rare trace gases at the South Pole. Antarctic Journal of the U.S., 18(5), 250-252. Rinsland, C.P., D.W. Johnson, A. Goldman, and J.S. Levine. 1989. Evidence for a decline in the atmospheric accumulation rate of CHC1F2 (CFC-22). Nature, 337(6207), 535-537. Solomon, S., M. Mills, L.E. Heidt, W.H. Pollock, and A.F. Tuck. 1992. On the evaluation of ozone depletion potentials. Journal of Geophysical Research, 97(D1), 825-842. Steele, L.P., P.J. Fraser, R.A. Rasmussen, M.A.K. Khalil, T.J. Conway, A.J. Crawford, R.H. Gammon, K.A. Masarie, and K.W. Thoning. 1987. The global distribution of methane in the troposphere. Journal ofAtmospheric Chemistry, 5(2), 125-171. UNEP (United Nations Environmental Program). 1987. Montreal protocol to reduce substances that deplete the ozone layer report (final report). New York: UNEP. Zander, R., M.R. Gunson, C.B. Farmer, C.P. Rinsland, F.W. Irion, and E. Mahieu. 1992. The 1985 chlorine and fluorine inventories in the stratosphere based on ATMOS observations at 30 0 north latitude. Journal ofAtmospheric Chemistry, 15(2), 171-186.
References Butler, J.H., J.W. Elkins, B.D. Hall, S.O. Cummings, and S.A. Montzka. 1992. A decrease in the growth rates of atmospheric halon concen-
Atmospheric longwave radiation spectrum and near-surface atmospheric temperature profiles at South Pole Station VON P. WALDEN and STEPHEN
G. WARREN, Geophysics Program, University of Washington, Seattle, Washington 98195
radiation spectrum coincident with the state of the atmosphere for use in our climate studies at the University of Washington. The data set spans the full year from 14 January 1992 through 14 January 1993. We are attempting to determine the controls of the longwave radiation budget on the antarctic plateau and to offer spectral measurements for use in testing atmospheric radiation models and radiation codes in climate models.
he antarctic atmosphere is the coldest and driest on T Earth. The downward clear-sky emission to the ice sheet in winter averages about 75 watts per square meter, that is, less than half that for the subarctic winter standard atmosphere (figure 1 and the table). In a collaborative effort at South Pole Station with Frank J. Murcray and Renate Heuberger of the University of Denver, we have compiled a data set of surface-based measurements of the downward
ANTARCTIC JOURNAL - REVIEW 1993
269
