Konrad Mauersberger

Measurement of heavy isotope enrichment in tropospheric ozone

Tropospheric ozone samples collected during a twelve-month period in urban air show an enrichment of about 9% in the heavy isotope 50O3 consistent with predictions from laboratory measurements. The enhancement of about 7% observed in 49O3 is still within the uncertainty of the expected value. These measurements confirm that the isotope effect, repeatedly found in laboratory experiments, is also produced in the atmosphere during the ozone formation process.

Surprising rate coefficients for four isotopic variants of O+O2+M

Mass spectrometric analysis of nonequilibrium oxygen isotopic mixtures undergoing UV photolysis has been employed to study three-body recombination rate coefficients for the O+O2, Q+O2, O+Q2, and Q+Q2 (O=16O, Q=18O) reactions, all with M=80% N2:10% O2:10% Q2 at 200 Torr and 296 K. kO+O2 is in good agreement with the currently recommended value, while kQ+Q2 is only slightly smaller. Surprisingly, kQ+O2 is close to kO+O2, while kO+Q2 is ≈50% larger. As a consequence of this unusual behavior, kO+OQ must be ≈20% larger than kQ+OQ to produce the well-known enrichments that occur in the free atmosphere and in laboratory experiments involving scrambled mixtures. Contrary to what is usually assumed in discussions of the heavy ozone anomaly, these results indicate that isotopic asymmetry does not guarantee a rate coefficient advantage.

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.

Relative formation rates of 50O3 and 52O3 in 16O–18O mixtures

Tunable diode laser (TDL) and mass spectrometry have been combined to measure relative formation rate coefficients of each of the four channels contributing to ozone of mass 50 u and 52 u produced in 16O–18O mixtures. Only one channel has a large rate coefficient advantage causing almost exclusively the observed isotope enrichment. Collisions to form ozone are end-on reactions. Molecular symmetry plays no apparent role in the ozone isotope enrichment process, regardless, whether or not ozone is produced in collisions with homo- or heteronuclear molecular oxygen. The oxygen isotope exchange process may hold a key in explaining the rate coefficient results.

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.

The Gas Chromatograph Mass Spectrometer for the Huygens Probe

The Gas Chromatograph Mass Spectrometer (GCMS) on the Huygens Probe will measure the chemical composition of Titans atmosphere from 170 km altitude (∼1 hPa) to the surface (∼1500 hPa) and determine the isotope ratios of the major gaseous constituents. The GCMS will also analyze gas samples from the Aerosol Collector Pyrolyser (ACP) and may be able to investigate the composition (including isotope ratios) of several candidate surface materials.The GCMS is a quadrupole mass filter with a secondary electron multiplier detection system and a gas sampling system providing continuous direct atmospheric composition measurements and batch sampling through three gas chromatographic (GC) columns. The mass spectrometer employs five ion sources sequentially feeding the mass analyzer. Three ion sources serve as detectors for the GC columns and two are dedicated to direct atmosphere sampling and ACP gas sampling respectively. The instrument is also equipped with a chemical scrubber cell for noble gas analysis and a sample enrichment cell for selective measurement of high boiling point carbon containing constituents. The mass range is 2 to 141 Dalton and the nominal detection threshold is at a mixing ratio of 10− 8. The data rate available from the Probe system is 885 bit/s. The weight of the instrument is 17.3 kg and the energy required for warm up and 150 minutes of operation is 110 Watt-hours.

Focusing of Aerosols into a Particle Beam at Pressures from 10 to 150 Torr

The study of aerosols including chemical analysis has been substan tially advanced after the development of aerodynamic focusing lenses. Test results of 2 such lenses are presented; 1 operating at pressures between 15 and 80 Torr and the other at higher pressures between 30 and 175 Torr. The lenses consist of 7 single orifices separated by spacers and contained in a tube of about 10 cm in length. Orifice diameters range from 1.40 to .25 mm, while the exit holes (nozzles) are smaller. Laminar gas flow within a lens produces a narrow particle beam which is directed into a vacuum chamber for analysis of beam width and position, aerosol transport efficiency, linearity, and other parameters. The lenses were tested both with spherical monodisperse oil particles (.34-4 mu m diameter) as well as nonspherical solid NaCl particles (.19-.85 mu m) simulating larger particles with lower density. Both lenses produce narrow aerosol beams with diameters smaller than 4 mm about 90 mm downstream of the nozzle. Although non...

Heavy Ozone--A Difficult Puzzle to Solve

Although not abundant, ozone is one of the most important constituents of the atmosphere. The isotopic variants of ozone, which is a symmetric triangular molecule made of three oxygen atoms, are difficult to explain by theoretical analysis. In their Perspective, Krankowsky and Mauersberger discuss results published in the same issue by Gellene (p. 1344) that shed light on the mechanisms responsible for the heavier isotopes of ozone.

Temperature dependence of ozone rate coefficients and isotopologue fractionation in 16O-18O oxygen mixtures

Abstract The temperature dependence of five ozone isotope-specific rate coefficient ratios and of isotopologue fractionation has been determined. Large formation rate coefficient ratios of 1.5 like 16 O + 18 O 18 O vs. 16 O + 16 O 16 O show no temperature dependence while small ratios such as 18 O + 16 O 16 O vs. 16 O + 16 O 16 O with a value of 0.92 decrease with decreasing temperatures. Temperature-related changes of isotopologue fractionation values for 50 O 3 and 52 O 3 are explained in terms of changes in rate coefficient ratios and contributions from isotope exchange reactions. The latter reactions exclusively control the large isotope fractionation of 54 O 3 while the rate coefficient ratio 18 O + 18 O 18 O vs. 16 O + 16 O 16 O remains constant at 1.02.

Pressure dependence of two relative ozone formation rate coefficients

Abstract The large enrichment observed in many ozone isotopomers has a pronounced pressure and temperature dependence and has been traced to rate coefficient advantages of certain formation channels. The pressure dependence of two relative rate coefficients 16 O + 18 O 18 O / 16 O + 16 O 16 O and 18 O + 16 O 16 O / 18 O + 18 O 18 O has been investigated. The first coefficient decreases as the ozone formation pressure increases from 40 to 3000 Torr, while the second remains unchanged. Reaction 16 O + 18 O 18 O which has a 50% higher rate of formation than 18 O + 16 O 16 O is therefore responsible for the decrease in isotope enrichment as the pressure of ozone formation increases.