Atmospheric constituents

Atmospheric constituents Trace gas and aerosol measurements to 30 kilometers in Antarctica

40 McMURDO, ANTARCTICA • JANUARY, 1976 o JANUARY, 1977 + JANUARY, 1978

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D.J. HOFMANN.J. M. ROSEN, A. L. FULLER, D. W. MARTELL, and G. L. OLSEN Department of Physics and Astronomy University of Wyoming Laramie, Wyoming 82071 A. L. SCHMELTEKOPF and P. D. GOLDAN Aeronomy Laboratory National Oceanic and Atmospheric Administration Boulder, Colorado 80302

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For the seventh consecutive austral summer, successful balloon measurements of stratospheric constituents were made in Antarctica. As in 1977, (Hofmann et al., 1977), nitrous oxide (N 20), chlorofluorocarbons (CF 2Cl2 and CFCI 3 ), aerosol particles (radius 0.15 micrometer or larger), and condensation nuclei (radius 0.01 micrometer or larger) were measured. The trace gases measured are important in determining the stratospheric ozone profile, and we now have an opportunity to begin studying long term time variations of these gases. The aerosol measurements are indicative of the level of major volcanic activity and are important in radiation balance studies. Condensation nuclei measurements are useful both in the troposphere and stratosphere, possibly affecting precipitation in the former and serving as seed parti cles for growth of the sulfate layer in the latter. The gas measurements are made by recovering air samples (five per flight at different altitudes) obtained during parachute descent from about 30 kilometers; these samples are analyzed by gas chromatography by the Aeronomy Laboratory of the National Oceanic and Atmospheric Administration in Boulder, Colorado (Schmeltekopf et al., 1977). The aerosol and condensation nuclei are measured in situ by light scattering particle counters which detect individual particles (Hofmann et al., 1975; Rosen and Hofmann, 1977). The N 20 profile was measured for the third consecutive year; these data are shown in figure 1. The tropopause occurred between 8 and 10 kilometers for these soundings. There is little time variation in the data below 20 kilometers; however, above this altitude there is considerable variation. The time scale of this variation is probably greater than 1 or 2 days as the 10 points in 1976 and 1977 were actually obtained from 2 balloon flights of 5 samples each taken 2 days apart in

October 1978

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N 2 0 MIXING RATIO (ppbv) Figure 1. Altitude profiles of nitrous oxide mixing ratio over McMurdo. (The mixing ratio is given in parts per billion by volume, ppbv) 1976 and 1 day apart in 1977. Variability in the N 20 profile was noted by Schmeltekopf and others (1977) in measurements at Laramie, Wyoming, and Fairbanks, Alaska. It appears that the time scale of such variations is of the order of several days to a week and probably is associated wth stratospheric transport processes. Figure 2 shows the results for the chlorofluorocarbons. Similar to the N 20 data, there is some variability at the highest altitudes. It is in the same sense as for the N 20 data, i.e., the air at 30 kilometers in 1977 contained a higher mixing ratio of trace gas than in 1978. This air could have been transported from lower latitudes where mixing ratios (at least for N 20) are observed to be higher (Schmeltekopf et al., 1977). Below about 25 kilometers there is little evidence for any time variation in the chlorofluorocarbons. Figure 3 shows a comparison of aerosol (r 0.15 micrometer) profiles taken in 1977 and 1978. Although the profiles in general are quite similar, there was less layering in the lower stratosphere in 1978 than in 1977. This probably indicates a lack of recent volcanic activity in 1978.

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Figure 2. Altitude profiles of chlorofluorocarbon mixing ratios over McMurdo. (The mixing ratio is given in parts per trillion by volume, pptv.)

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Figure 4. Condensation nuclei (R0.01 micrometer) concentration profiles obtained at the South Pole. (The arrows mark the observed position of the tropopause.)

1978 sounding shown in figure 4, we also conducted three short soundings (to about 5 kilometers) which confirmed these high troposopheric concentrations. At present, we find it difficult to bring our results into agreement with groundbased measurements of CN at the South Pole, which generally show much lower concentrations. This work was supported in part by National Science Foundation grants DPP 76-17777 and DPP 77-21202 and by Department of Commerce grant 04-6-002-44019. Messrs. Fuller, Martell, and Olson performed the field work at McMurdo and South Pole between 2 January and 6 February 1978.

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Figure 3. Aerosol particle (r0.15 micrometer) concentration profiles obtained at McMurdo. (The smooth lines are lines of constant mixing ratio in units of particles per milligram of air. The arrows mark the observed position of the tropopause.)

Figure 4 shows a comparison of condensation nuclei (cN) profiles for 1977 and 1978. The profiles are nearly identical except for the tropopause region (near 10 kilometers). It is characteristic of CN profiles to decrease drastically at the tropopause. We again saw the high tropospheric concentrations of CN we thought were unusual in 1977. In addition to the

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Hofmann, D. J . , J. M. Rosen, G. L. Olson, N. T. Kjome, A. L. Schmeltekopf, and P. D. Goldan. 1977. Measurements of trace gases and aerosols in the Antarctic stratosphere. AntarctzcJournal of the U.S., 12(4): 162. Hofmann, D.J.,J. M. Rosen, T. J. Pepin, and R G. Pinnick. 1975. Stratospheric aerosol measurements I: Time variations at northern mid latitudes. Journal of the Atmospheric Sciences, 32: 1446. Rosen,J. M., and D.J. Hofmann, 1977. Bailoonborne measurements of condensation nuclei.Journal of Applied Meteorology, 16: 56. Schmeltekopf, A. L., D. L. Albritton, P.J. Crutzen, P. D. Goldan, W. J. Harrop, W. R. Henderson,J. R. McAfee, M. McFarland, H. I. Schiff, T. L. Thompson, D.J. Hofmann, and N. T. Kjome. 1977. Stratospheric nitrous oxide altitude profiles at various latitudes. Journal of the Atmospheric Sciences, 34: 729.

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