HR: 0800h
AN: A21B-0729    [Abstracts]
TI: Observations of Chloroform (CHCl$_3$)-Depleted Air Masses at the Jungfraujoch High-Altitude Observatory
AU: * Vollmer, M K
EM: martin.vollmer@empa.ch
AF: Air Chemistry Department, Swiss Federal Laboratories for Materials Testing and Research, Uberlandstrasse 129, Dubendorf, 8600 Switzerland
AU: * Vollmer, M K
EM: martin.vollmer@empa.ch
AF: Biogeochemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, Mainz, 55020 Germany
AU: Reimann, S
EM: stefan.reimann@empa.ch
AF: Air Chemistry Department, Swiss Federal Laboratories for Materials Testing and Research, Uberlandstrasse 129, Dubendorf, 8600 Switzerland
AU: Stemmler, K
EM: konrad.stemmler@psi.ch
AF: Laboratory for Radiochemistry and Environmental Chemistry, Paul Scherrer Institute, Villigen, Villigen, 5232 Switzerland
AU: Schaub, D
EM: daniel.schaub@empa.ch
AF: Air Chemistry Department, Swiss Federal Laboratories for Materials Testing and Research, Uberlandstrasse 129, Dubendorf, 8600 Switzerland
AU: Folini, D
EM: doris.folini@empa.ch
AF: Air Chemistry Department, Swiss Federal Laboratories for Materials Testing and Research, Uberlandstrasse 129, Dubendorf, 8600 Switzerland
AB: Episodes of chloroform (trichloromethane, CHCl$_3$) depletion in air masses have been observed over the past 4 years at the high-altitude (3580 m.a.s.l) research station at Jungfraujoch, Switzerland, using in situ gas chromatography-mass spectrometry (GC-MS) measurement techniques. These $\sim$10 episodes occurred primarily during winter and early spring time and lasted typically 1 to 3 days. They are characterized by chloroform concentrations below 2 pmol mol$^{-1}$ compared to a mean background concentrations of $\sim$10 pmol mol$^{-1}$ over the observational period. Relative humidity during these episodes is very low, suggesting a recent stratospheric origin of the air masses. However, positive ozone anomalies are absent for these episodes. In addition, backtrajectory analysis suggests that the air masses resided in the upper troposphere in northern and north-eastern Europe for at least 5 days prior to the arrival at Jungfraujoch. Also, other chlorinated trace gases with similar known atmospheric sinks, such as CH$_2$Cl$_2$ and CH$_3$CCl$_3$, are not depleted during these episodes. Our findings are therefore suggestive of an unknown selective removal mechanism for chloroform in the upper troposphere or lower stratosphere.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting