Christa Fittschen - Directrice de Recherche CNRS
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Research activities
- kinetic studies of atmospheric chemistry interest by laser photolysis at low pressure coupled with LIF (OH) and cw-CRDS (HO2)- - metrology of OH and HO2 in the atmosphere and kinetic studies applied to combustion and atmospheric chemistry by FAGE
- - kinetic studies of photocatalytic chemistry by lamp photolysis coupled with LIF (OH) and cw-CRDS (HO2)
Research topics :
- -kinetic studies of atmospheric chemistry interest by laser photolysis at low pressure coupled with LIF and cw-CRDS
The hydroxyl radical, OH, and the HO2 radical with which it is forms a rapid pseudo-equilibrium is responsible for a vast number of chemical reactions in the atmosphere.
This enables the generation of radicals by laser photolysis in a low-pressure cell and subsequent time-resolved monitoring of the concentrations of OH and HO2 and thus the kinetics of the reaction under investigation (depending on which reagents are added to the cell).
The setup is made by three main different parts :
- the photolysis cell where the radicals will be created at a time t0 by the photolysis laser pulse in a gas mixture appropriated
- the cw-CRDS (continuous wave Cavity Ring Down Spectroscopy) detection for HO2 constituted mainly by a light source (laser diode), a cavity (2 mirors with a high reflectivity), a detector (photodiode) and a AOM permitting to switch the light.
- the LIF (Laser Induced Fluorescence) detection for OH constituted by an excitation laser (dye laser at 282 nm, 10 kHz), a detector (CPM : channel photomultiplier) permitting to detect the OH fluorescence around 308 nm
- - metrology of OH and HO2 in the atmosphere and kinetic studies applied to combustion and atmospheric chemistry by FAGE
- Aim :
-
The OH and HO2 radicals, are major reactive species in the atmospheric chemistry but also in combustion, two research topics developed in our laboratory, the PC2A.
It’s why we have built a new instrument, mobile for the absolute quantification of OH and HO2 based on the very sensitive and selective technique of Florescence Assay by Gas Expansion (FAGE), the first of its kind in
In the atmosphere, the hydroxyl radical, OH, is the primary atmospheric oxidant, initiating the oxidation of the majority of the chemical species in the atmosphere. It is therefore essential to obtain absolute concentrations of OH in the atmosphere to be used as input data for comparison or for the modelling of atmospheric chemistry. Our instrument will be used to participate to measurement campaigns in a multitude of different environments (clean air, polluted air, forested sites, marine sites, etc.) to study all the different and varied chemical mechanisms in which OH is involved. Afterwards, the campaigns take place only periodically. Then in order to optimise the use of the instrument, we are adapting it to kinetic measurement linked to combustion phenomena.
In combustion, we are interested by the HO2 reactivity. Indeed, HO2 plays an important role in the combustion mechanismes at “low temperature” (T < 1000K) taking place in engine, for example. It is planed to couple the FAGE detection cell with a cell permitting to work at variable pressures and temperatures to measure rate constant and branching ratio of different chemical pathways of reactions involving HO2
Principle of the setup : - The setup can have different configurations :
- - the FAGE cells alone permit to probe ambiant air and to measure atmospheric OH and HO2
- - the FAGE cell coupled with a photolysis cell working at atmospheric pressure and temperature to do kinetic studies in the atmospheric conditions
- - theFAGE cell coupled to a photolysis cell working at variable pressure and temperature (up to 10 bars, 1000 K, to be built) to study reactions in the low temperature regime of combustion
- - In a near futur, a TOF-MS (Time of Flight MAss Spectrometer) will be installed at the exit of the FAGE cell to measure stable species
- The FAGE setup is based on the Laser Induced Fluorescence (LIF) on OH after gaseous expansion. By pumping, a fraction of the reaction mixture is expanded continuously into a low pressure cell, coupled to a sensitive detection of OH radicals by high repetition LIF (laser induced fluorescence).
- The detection of OH by
LIF is based on a selective excitation at 308nm (A-X(0-0) and detection at the
same wavelength. The fluorescence is proportional to the OH concentration;
obtaining absolute concentrations need a calibration procedure. The expansion
into a low pressure cell is necessary to (a) freeze the chemical reactions and
(b) increase the fluorescence lifetime of OH through a decrease of the
quenching. The high sensibility of the FAGE technique, necessary for
atmospheric OH concentration measurement, is obtained by a high repetition
laser (5-10 kHz); advantage of this high repetition rate laser is taken in the
kinetic experiments to obtain good time resolution (200µsec).
- The HO2 measurement is based on a chemical conversion in OH detected by LIF via the fast reaction HO2 + NO given OH + NO2.
This instrument (as it is based on LIF) requires calibration by generating a gas mixture containing a known concentration of OH. This is achieved by photolysis of a mixture air and water vapour with a mercury lamp. The concentration of OH can be found by measuring the concentration of water and the light output of the lamp.
- - kinetic studies of photocatalytic chemistry by lamp photolysis coupled with LIF (OH) and cw-CRDS (HO2)
- Aim :
Evaluation of HOx radical formation potential at the vicinity of irradiated model
photocatalytic
The photocatalytic surface investigation
reactor consists of a stainless steel chamber equipped with a planar moveable support
along x axis, where the photocatalytic materials is deposited.
Continuous UV
irradiation will come from a Hgdischarge lamp, placed opposite of the material
surface.
Various gases (O2, N2, Ar, H2O, VOC) can be
admitted to thereactor at variable pressure.
Spectroscopic measurements are performed
along y axis. LIF is dedicated to OH investigation and cw-CRDS will enable HO2, HCHO and H2O2 detection.
- Coordinator of Marie-Curie EST project TOTECAT under
FP6, project
including 8 PhD grants
- Coordinator of ARCUS (Action Regionale de
Collaboration Universitaire et
Scientifique) PhyCAFoR, co-funded by French Minister of Foreign and
European
Affairs and the Region Nord-Pas de Calais, involving 5 laboratories in
Nord-Pas
de Calais and 5 laboratories in Czech Republic, Hungary and Romania
- PI of a work package in French-German CNRS-DFG project
- Coordiantor of a PICS (Projet international de collaboration
scientifique)
with University of Karlsruhe
- Coordinator of ECO-NET (Europe Centrale et Occidentale Networking)
project
pooling 6 laboratories in Hungary , Czech Republic
and
Romania.
- Coordination of several LEFE-CHAT projects (French national research
project,
sponsored by CNRS)
Organisation
of international and national conferences
- Member of Royal Society of Chemistry Gas Kinetic Committee organising
the
biannual “International Symposium on Gas
Kinetics”
(1 week, 200 participants)
- Head (1 of 3) of “French Group of Kinetics and
Photochemistry”, organising
the annual national group meeting (2 days, 50-80 participants)
- Co-organisation (33%) of International Summer School
“Physics and chemistry
of the atmosphere: from laboratory experiments to field campaigns”
in
Constanta, Romania, July 2008 (1 week, 100 participants)
- Organisation of “Marie-Curie EST Joint meeting”
between 2 Marie-Curie EST
networks, TOTECAT (Lille) and BREATHE (Bristol) in Lille, June 2008 (3
days, 50
participants)
- Co-organisation (33%) of workshop “Interface between
Spectroscopy and
Atmospheric Chemistry II”, Marseille, June 2007 (2 days, 50
participants)
- Co-organisation (50%) of a joint
meeting “Modern Techniques in Atmospheric
Physics and Chemistry”
in
Szeged, Hungary, Mai 2007
(3
days, 60 participants)
- Co-organisation (33%) of summer school “Physics and
chemistry of the
atmosphere: from laboratory experiments to field campaigns” in Iasi, Romania, July 2006 (2
weeks, 150
participants)
- Co-organisation (33%) of workshop “Interface between
Spectroscopy and
Atmospheric Chemistry I”, in Lille, June 2005 (2 days, 50
participants)
- Organisation of “4th International
CRDS user meeting” in Lille,
Sept. 2003 (2 days, 100 participants)
- 11.
Djehiche,
Mokthar
-
Mechanism of the Degradation
of Oxygenated Organic Compounds in an Atmospheric Simulation Chamber,
co-Advisor, started in October 2008
- 10. Jain, Chaithanya
-
Study of the reactivity of HO2
radicals by laser photolysis
/ cw-CRDS and Laser Induced Fluorescence, Advisor, started in November
2008
- 9. Bettinelli,
Claudio
-
Degradation of Volatile Organic Compounds by
laser photolyse / Tuneable
Diode Laser Absorption Spectroscopie TDLAS ; Advisor, started
in Septembre
2007
- 8. Szabo,
Emese
-
Photolysis of Volatile Organic Coumpounds in an
atmospheric simulation
chamber, Co-adivsor
in a co-tutelle with
Sandor Dobé at the Academie of Sciences in
- 7. Tarmoul,
Jérémy
-
Reactivity of HO2
radicals studied by in-situ cw-CRDS in an
atmospheric simulation chamber, Co-advisor with Partice Coddeville at
Ecole des
Mines de
- 6. Thiébaud,
Jérôme
-
Development of a high finesse optical cavity
coupled to a laser
photolysis reactor – Spectroscopique and kinetic measurement
HO2 radical,
Advisor, defended in 2007
- 5. Crunaire,
Sabine
-
Development of a cw-CRDS spectrometer and its
application to kinetic
studies in an atmospheric simulation chamber, Advisor, defended in 2005
- 4. Turpin,
Estelle
-
Kinetic and mechanism of the degradation of
three volatile organic
compounds : acetone, phenol and catechol : combined
study in a fast
flow reactor and an atmospheric simulation chamber , Advisor, defended
in 2004
- 3. Delbos,
Eric
-
Application
of laser photolysis and laser induced fluorescence to the kinetic study
of
vinoxy type radicals, Advisor, defended in 2004
- 2. Hassouna,
Melynda
-
Application of laser photolysis to the kinetic
and spectroscopic study
of CBr, HCBr,
C2H3O, C3H5O radicals,
Co-Advisor, defended in 2000
- 1. Delcroix,
Bruno
-
Kinetics and Spectroscopie
of atmospherically interesting radicals produced by laser photolysis,
Co-Advisor,
defended in 1998