NOAAIGMCC halocarbonand nitrous oxide

measurements at the South Pole

JAMES W. ELKINS and THAYNE M. THOMPSON

National Oceanic and Atmospheric AdministrationGeophysical Monitoring for Climatic Change Division

Boulder, Colorado 80303

BRAD D. HALL, KEITH B. EGAN, and JAMES H. BUTLER

Cooperative Institute for Research in Environmental SciencesBoulder, Colorado 80309

There is strong evidence for the theory that the antarcticozone hole is primarily due to chlorine-catalyzed destructionof ozone from increased anthropogenic releases of halocarbonsF12 (CC12F2) and Fil (CC13F) into the atmosphere (Tuck et al.in press). Nitrous oxide is the primary source of stratosphericnitric oxide, and nitric oxide, like F12 and Fil, can depletestratospheric ozone (Crutzen 1970). Nitrous oxide, F12, andF11 are strong infrared absorbers and may have an importantrole in the radiative budget of the Earth (Wang et al. 1976).Monitoring these compounds in a remote site can provideuseful information about their accumulation rates in the back-ground atmosphere.

The Geophysical Monitoring for Climatic Change (GMCC)division of the National Oceanic and Atmospheric Adminis-tration (NOAA) has been analyzing flask samples for nitrousoxide and halocarbons F12 and Fli collected from the SouthPole since 1977. Care was taken to avoid contamination of thesamples by reducing contact with elastomers in the valves andby sampling air only in the clean-air sector (110° to 330°) of theclean-air facility. Prior to 1983, a pair of flask samples wascollected semi-monthly during the antarctic summer andmonthly during the rest of the year, and then shipped to theGMCC labs in Boulder for analysis. Since flasks can be shippedfrom the South Pole only 3 months a year, flasks collectedduring the antarctic winter required a long storage period be-fore shipment to Boulder for analysis.

During the summer of 1983, a manually operated gas chro-matograph was installed at the South Pole to eliminate samplestorage time in flasks. The gas chromatograph has been run 1day a week, beginning with two initial calibration gas injec-tions, then two injections of outside air from the clean-airsector, and followed by another calibration analysis. With theinstallation and operation of the gas chromatograph, the fre-quency of sampling by flasks has been reduced to a pair offlasks collected once a week only during the antarctic summer.More technical information on the design of the flasks, gaschromatograph experimental conditions, and data selection aregiven in Thompson, Komhyr, and Dutton (1985) and Robinsonet al., (1988).

The figure shows the concentration and trends for nitrousoxide, F12, and Fil for both flasks and the in situ gas chro-matograph at the South Pole. The growth rate of nitrous oxidein the atmosphere above the South Pole from NOAA/GMCCflask samples taken between 1977 and 1987 is 0.66 ± 0.07 (95percent confidence level) parts per billion per year. This rateagrees (within the experimental uncertainties) with the results

of Howard et al. (1986) of 0.6 parts per billion per year during1982-1986 at Palmer Station (65°S 64°W) and Weiss (1981) of0.52 ± 0.13 (63 percent confidence level) parts per billion peryear during 1976-1980 at the South Pole. Our nitrous-oxidegrowth rate is lower than the results by Rasmussen and Khalil(1986) of 1.04 ± 0.14 (90 percent confidence level) parts perbillion per year during 1975-1985 at the South Pole. The cal-culated growth rates of F12 and Fil at the South Pole fromNOAA/GMCC flask samples during the 1977-1987 period was16.3 ± 0.5 (95 percent confidence level) and 9.3 ± 0.5 partsper trillion per year, respectively. Data from Rasmussen andKhalil (1986) yielded growth rates during the 1975-1985 periodfor F12 and Fli at the South Pole of 18.4 ± 1.1 (95 percentconfidence level) and 10.4 ± 0.9 parts per trillion per year,respectively. Howard et al. (1986) measured growth rates forF12 and Fli during the 1982-1985 period at Palmer Station of17.5 and 11.0 parts per trillion per year, respectively. Fromdata presented in Cunnold et al. (1986) for Cape Grim, Aus-

aO Flask+ in situ CC

WE02011ilm00q3

Slope=066 E 0.07 ppb yr290

77 78 7 ii9 80 81 82 83 84 85 86 87 88TIME (YEAR)

bO Flask+ in Situ CC

Slope=16.3 ± 0.5 ppt yr'

77 78 79 80 81 82 83 84 85 86 87 88TIME (YEAR)

1001ii'i'i'r'IIIII77 78 79 80 81 82 83 84 85 86 87 88TIME (YEAR)

Concentration of atmospheric (a) nitrous oxide (N 20) (In parts perbillion), (b) F12 (in parts per trillion), and (c) Fli (in parts per tril-lion), at South Pole from flasks (o) and monthly means from an In

situ gas chromatograph (+). Trends are calculated from the flasksamples only. The absolute calibration scales for nitrous oxide andthe halocarbons are based on the National Bureau of Standardsscale of J. Elkins and the Oregon Graduate Center scale of R.Rasmussen, respectively.

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tralia (41°S 143°W), we calculated growth rates of F12 and Filduring the 1978-1983 period of 16.5 ± 0.4 (95 percent confi-dence level) and 9.4 ± 0.2 parts per trillion per year, respec-tively.

In 1988, we improved our existing in situ gas chromatographby automating the analyses, by increasing the frequency ofanalysis to sampling the atmosphere once every 3 hours, andby adding two new compounds, methyl chloroform and car-bon tetrachloride. These improvements may help resolve cer-tain questions concerning the vertical transport at the SouthPole and its effect on the ozone hole.

This work is funded by NOAA but has received generouslogistical and technical support from the Division of Polar Pro-grams of the National Science Foundation. We would like tothank W. Komhyr who started this program at the South Poleand the National Science Foundation for supporting this pro-gram.

References

Crutzen, P.J. 1970. The influence of nitrogen oxides on the atmosphericozone content. Quarterly Journal of the Royal Meteorological Society, 96,320-325.

Cunnold, D.M., R.G. Prinn, R.A. Rasmussen, P.C. Simmonds, F.N.Alyea, C.A. Cardelino, A.J. Crawford, P.J. Fraser, and R.D. Rosen.1986. Atmospheric lifetime and annual release estimates for CFC13and CF2C12 from 5 years of ALE data. Journal of Geophysical Research,91(D10), 10,797-10,817.

Howard, H.M., D.G. Cronn, W.L. Bamsberger, and F.A. Menzia.1986. Air chemistry monitoring at Palmer station. Antarctic Journalof the U.S., 21(5), 250-251.

Rasmussen, R.A., and M.A.K. Khalil. 1986. Atmospheric trace gases:Trends and distributions over the last decade. Science, 232, 1,623-1,624.

Robinson, E., B.A. Bodhaine, W.D. Komhyr, S.J. Oltmans, L.P. Steele,P. Tans, and T.M. Thompson. 1988. Long-term air quality moni-toring at the South Pole by the NOAA program Geophysical Mon-itoring for Climatic Change. Reviews of Geophysics, 26, 63-80.

Thompson, TM., W.D. Komhyr, and E.G. Dutton. 1985. Chlorofluo-rocarbon-li, -12, and nitrous oxide measurements at the NOAAIGMCC baseline stations (16 September 1973 to 31 December 1979).NOAA Technical Report ERL 428-ARL 8, Boulder, Colorado: Environ-mental Research Laboratories.

Tuck, A.F., and others. In press. Synoptic and chemical evolution ofthe Antarctic vortex in late winter and early spring, 1987: An ozoneprocessor. Journal of Geophysical Research.

Wang, W.C., Y.L. Yung, A.A. Lacis, T. Mo, and J.E. Hansen. 1976.Greenhouse effect due to man-made perturbations of trace gases.Science, 194, 658-690.

Weiss, R.F. 1981. The temporal and spatial distribution of troposphericnitrous oxide. Journal of Geophysical Research, 86(C8), 7,185-7,195.

Atmospheric methane, ice ages,and population:

A graphical review ofmethane concentrations

over the past 160,000 years

M.A.K. KHALIL and R.A. RASMUSSEN

Institute of Atmospheric SciencesOregon Graduate CenterBeaverton, Oregon 97006

During the past 8 years or so, there has been renewed in-terest in the global cycle of atmospheric methane, because itsconcentrations are increasing at about 1 percent per year. Suchincreases may add to global warming expected from increasinglevels of carbon dioxide, affect atmospheric chemistry by add-ing ozone and carbon monoxide to the lower atmosphere, andreduce the oxidizing capacity of the Earth's atmosphere bydepleting hydroxyl ion radicals (see references in WMO, 1985).

Atmospheric concentrations of methane have been deducedfrom analyses of polar ice cores, which extend the record backsome 160,000 years. Direct atmospheric measurements, usinggas chromatography, span the last 25 years and systematictime series exist only for the last decade (Rasmussen and Khalil1986; Khalil and Rasmussen 1987). Data on the ice age about20,000 years ago come from Stauffer et al. (1988) based onanalyses of the Byrd and Dye 3 cores. Data from the ice age

some 150,000 years ago come from Raynaud et al. (1988) basedon analyses of the Vostok core. The remaining data are fromthe various cores, including the Dye 3 and Byrd cores, storedat the State University of New York's ice storage facilities (Khaliland Rasmussen 1982, 1987; Craig and Chou 1982; Rasmussenand Khalil 1984; Stauffer et al. 1985). Here we show a synthesisof all the data in the figure.

There are two main features in the figure. During the iceages, methane concentrations dip to the lowest values ob-served (about 300-350 parts per billion by volume), and inrecent years, there is a very rapid buildup from a natural back-ground of about 600 parts per billion by volume to the presentconcentrations of about 1,650 parts per billion by volume. Mostof the increase has taken place over the last century.

The two features are probably controlled by the change ofemissions. During the ice ages, emissions from wetlands andother ecosystems are greatly reduced, causing a proportionatereduction in methane concentrations. Therefore, natural var-iations of climate, as reflected in the temperature records, affectmethane concentrations over long time scales of tens to hundredsof thousands of years. The Earth's temperature is also likelyto be affected to some extent by the change of methane causinga climatic feedback. In the figure, we have shown estimatesof Northern Hemisphere temperatures along with the methaneconcentrations for periods up to the last 10,000 years. Thetemperature data are as compiled by Watts (1982). The rapidrise of methane in recent times is apparently unlike any periodin the past 160,000 years. The increase over the past 200 yearsor so follows closely the rapid rise of population, which hasbrought with it increasing demands for food and energy (Ehr-lich et al. 1977). The increased production of rice, natural gas,and cattle populations is likely to be a significant cause for

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