P. Lämmerzahl

Stratospheric ozone isotope enrichments - revisited

Ozone isotope data for 49O3 and 50O3 are presented, that were obtained from 28 stratospheric samples collected over 10 years onboard balloon payloads. Enrichments for 49O3 range from 7 to 9% in the middle stratosphere. This is in very good agreement with laboratory-derived isotope predictions. For 50O3 most enrichments are between 7 and 11%, a few, however, are too high to be of atmospheric origin. Arguments are presented that stratospheric ozone isotope data are consistent with enrichments determined in laboratory studies when pressure and temperature dependence of the isotope effect is included. Results from recent remote sensing experiments support the values obtained during balloon-borne sample collections. Very high enrichments occasionally measured in the past should be disregarded.

Isotopic measurements of stratospheric ozone

Isotope ratios of stratospheric ozone samples collected during four balloon flights are reported. In an altitude range between 22 and 33 km all ratios show enrichments between 7 and 11%, somewhat lower for 49 O 3 than for 50 O 3 . Those enrichments are in very good agreement with results from laboratory isotope studies when stratospheric pressure and temperatures are included. The new data presented do raise questions about past stratospheric ozone isotope measurements which sometimes showed high values never observed in the laboratory or tropospheric environment.

Gas release from ice/dust mixtures

Gas fluxes from insolated ice/dust mixtures were measured by pressure gauges and a mass spectrometer placed one meter in front of the sample. As soon as the insolation of about one solar constant was started a fast rise in H2O and CO2 emissions from the fresh surface was observed. Thereafter gas fluxes slowly decreased. When intermittent dark periods occurred, water emission dropped rapidly while CO2 fluxes were measured for hours. Results from labeled isotope layers gave information on sublimation depth and temperature and showed that sublimated CO2 migrated also toward deeper parts of the sample where it recondensed, producing an enrichment. A simple model is presented which describes the redistribution of CO2 within the sample consistent with the gas phase and solid phase measurements of CO2 abundances.

Measurement of the volatile component in particles emitted from an ice/dust mixture

A set of novel instruments has been developed to measure the volatile component of solid particles emitted from the surface of an insolated ice/dust mixture (“sample”). To detect such particles a pressure gauge is mounted inside a volume which has a narrow tube placed on top for particles to enter. The experiments are positioned about 0.5 m away from and below the sample. Particles, after falling through the tube are collected in a heated cup, ices evaporate and produce a gas pulse inside the volume. The pressure, registered by the gauge, will decrease with a time constant of about 0.4 s. In some instruments the single cup is replaced by a multiple cup collector. In recent comet simulation experiments (KOSI 5 and KOSI 6) with ice/dust mixtures over 1200 gas pulses were observed. They fall into two categories: (a) short pressure pulses with a fast rising amplitude followed by the expected exponential decay, and (b) long pulses with rise times of about one second and several tens of seconds decay times. The former pulses are associated with ice particles, whereas the latter pulses are attributed to skeleton silicate grain agglomerates which have ice imbedded in them. The estimated mass distribution ranges from 2 × 10−10 g to 10−5 g of volatile material. Ice particles are emitted at maximum rate immediately at turn-on of the artificial sun and drop to much lower frequencies within less than one hour. “Mineral” particles, in contrast, reach their maximum frequency later, with their abundance also decreasing but less pronounced. Since gas emission varies very little while the ice particle frequency drops rapidly, it appears that the particle rate is not controlled by the gas fluxs drag force, but by the availability of particles suited for acceleration at the surface of the sample.