• Chemical kinetics and mechanismus of interfacial reaction on substrates of atmospheric interest and other technologically important materials.
• Time-resolved and steady state measurements in Knudsen flow reactors using mass spectrometric and laser-based analytical techniques.
• Measurements of surface residence times of non-reacting and reacting molecules under the constraint of saturable surfaces.
• Physico-chemical characterization of laboratory-generated aerosols.
• Characterization of surface species using FTIR spectroscopy after contamination of water ice by different trace gases under atmospheric relevant conditions.
• Box model calculations addressing a realistic description of heterogeneous chemistry under upper tropospheric and lower stratospheric conditions.
• Chemical-kinetic modeling of interfacial reaction mechanismus.

Knudsen flow reactor experiments
This equipment is devoted to the study of the uptake of atmospheric trace gases onto surrogate atmospheric particles such as salt, soot, secondary organic aerosols, ices and mineral dust, as well as of reaction products in order over the temperature range 140 to 700K in order to unravel the reaction mechanism from a fundamental point of view.  Such mechanistic understanding enables the extrapolation or experimental results to atmospherically relevant conditions. Click here for more information.  

Molecular Diffusion Tube experiments
A heterogeneous reaction will be efficient when the adsorbed gaseous species will rather undergo a surface reaction rather than desorption.  This simple idea is embodied in the title experiment where a pulse of sample molecules propagates through a sample tube coated with the substrate of interest (salt, soot, mineral dust) under molecular diffusion conditions.  The time-dependent MS signal owing to effusion of the molecules out of the coated sample tube into the detection chamber provides information on the surface residence time, the uptake coefficient and the number of adsorption sites after fitting to a Monte Carlo-based trajectory code.  In contrast to the Knudsen flow reactor the emphasis is placed on the study of the surface residence time (or inverse of the desorption rate constant). Click here for more information.  

Multidiagnostic stirred flow reactor
This chamber experiment is designed to study the chemical kinetics and spectroscopy of thin film surrogates of ice particles in the range 130 to 260K such as Cirrus cloud and aviation contrail particles using the following four diagnostic techniques:

• Residual gas mass spectrometry (MS)
• HeNe interferometry for the real-time in situ study of changes in thin ice film thickness
• FTIR transmission and grazing incidence absorption of thin films in the range
• Quartz crystal microbalance (QCMB) of mass change of thin cryogenic thin films.

The virtue of this chamber is that it enables both kinetic and spectroscopic information on the gas as well as the condensed phase under identical experimental conditions enabling thermochemical closure of for instance condensation (uptake) as well as evaporation rates of ices contaminated with HCl, HBr and HNO3.  One of the key features of this system is that the IR optical window as well as the QCMB active element is the only temperature-controlled cold spot in the chamber thereby enabling quantitative cross calibration of the different diagnostics. Click here for more information.  

Aerosol Reactor
This effort is designed to investigate either the formation of Secondary Organic Aerosols (SOA) from appropriate molecular precursors in the presence of UV radiation using an atmospheric pressure minireactor with on-line mass spectrometry as well as aerosol metrology (DMA-CNC combination) on the one hand, and heterogeneous reactions of atmospheric trace gases such as HOCl, HNO3 and HOBr on salt aerosols as a function of atmospheric parameters such as temperature and relative humidity.  These studies have revealed the importance of deliquescence and atmospheric acidity for chemical reactions involving aerosol particles.  In addition, the combination of the collection on a Teflon membrane filter of an aerosol generated in an atmospheric minireactor from olefin/O3 or toluene/O3/hn with subsequent chemical titration of the supported aerosol in the Kudsen flow reactor using specific molecular probes affords the quantitative investigation of the functional groups of submicron aerosol particles rather than the bulk chemical composition.  Examples of molecular probes are NO2 and O3 for reducing sites, N(CH3)3 for acidic sites and NH2OH for carbonyl groups. 

The Nature of the Interface and the Diffusion Coefficient of HCl/Ice and HBr/Ice in the Temperature Range 190-205K, A. Aguzzi, B. Flückiger and M. J. Rossi, Phys. Chem. Chem. Phys. 2003, 5, 4157-4169 (DOI: 10.1039/b308422c).

The Heterogeneous Interaction of Br2, Cl2 and Cl2O with solid KBr and NaCl Substrates:  The Role of Adsorbed H2O and Halogens, Ch. Santschi and M. J. Rossi, Phys. Chem. Chem. Phys., 6, 3447-3460, 2004 (DOI:  10.1039/b404415k).

Can Soot Particles Emitted by Airplane Exhaust contribute to the Formation of Aviation Contrails and Cirrus Clouds ?  C. Alcala-Jornod, H. van den Bergh and M. J. Rossi, Geophys. Res. Lett. 2002, 29, 1820 (doi 10.1029/2001GL014115).

The Heterogeneous Reaction of NO2 with NH4Cl:  A Molecular Diffusion Tube Study, N. Takenaka and M. J. Rossi, J. Atmos. Chem. (2004, in press). 

The Rate of Water Vapor Evaporation from Ice Substrates in the presence of HCl and HBr:  Implications for the Lifetime of atmospheric Ice Particles, C. Delval, B. Flückiger and M. J. Rossi, Atmos. Chem. Phys. Discuss. 2003, 3, 2179-2218, Atmos. Chem. Phys. 2003, 3, 1131-1145.

The kinetics of condensation and evaporation of H2O from pure ice in the range 173 to 223K:  a quartz crystal microbalance study, Ch. Delval and M. J. Rossi, Phys. Chem. Chem. Phys. 2004, 6, 4665-4676 (DOI:10.1039/B409995H).

The surface properties of SOA generated from limonene and toluene using specific molecular probes: a new experimental technique, B. Demirdjian and M. J. Rossi, submitted to Environmental Science and Technology (2004).

The Characterization of Surface Functional Groups of Secondary Organic Aerosols (SOA) generated under Laboratory Conditions, B. Demirdjian and M. J. Rossi, Proceedings of the EC/EUROTRAC-2 Joint CMD-Workshop, Paris 2002, pg. 219-224.