Physico-chemical approach to improve the knowledge of the impact of biogenic VOCs and their degradation products on the global climate. Expertise of the teams includes laboratory studies of elementary processes and complex mechanisms coupled with theoretical approaches as well as field experiments.
Illustration : Great Smoky Mountains National Park: formation of aerosols from biogenic VOCs
Introduction
The emission of biogenic VOCs such as isoprene (C5H8) and terpenes (C5H8)n overruns largely the amount of VOCs emitted through human activity. The oxidation products of these biogenic VOCs are often source of new particle formation, depending on parameters such as temperature, humidity and particularly NOx concentration. The degradation of these biogenic VOCs can also largely influence global climate through a change in the oxidizing capacity of the atmosphere, influencing directly the OH-budget and hence the lifetime of green house gases such as methane. Until recently it was thought that the degradation of these biogenic VOCs would decrease the overall oxidizing capacity of the atmosphere through net consumption of HOx radicals. However, recent field campaigns in tropical forests in Surinam and Borneo have found unexpected high OH concentrations, inconsistent with model calculation, and have put into question the so far accepted degradation mechanism of biogenic VOCs. New mechanisms, largely influencing the global OH budget and questioning the impact of these biogenic VOCs on the global aerosol load, have been proposed based on ab-initio calculations. Biogenics VOCs is a hot topic, and it will be a challenging priority for the next few years.
Materials and methods
Laboratory equipement:
Technique cw-CRDS coupled to laser photolysis (worldwide unique).
High resolution spectrometers (2 GHz – 1.5 THz) of very high sensitivity.
Simulation chamber equipped with innovative optical detection methods (IBB-CEAS).
Atmospheric simulation chamber coupled with cw-CRDS.
Innovative experimental set-up at the French synchrotron SOLEIL :
coupling of a molecular beam to synchrotron radiation (Jet-AILES apparatus)
Multi-pass IRTF cell coupled with synchrotron radiation.
Coupling of an atmospheric simulation chamber to a mass spectrometer using synchrotron radiation for photo-ionisation (PIMS).
Coupling of a fast flow reactor to PIMS.
Field experiment :
Participation to the ChArMeX (Chemistry-Aerosol Mediterranean Experiment) campaign in Corsica (February 2012 – August 2013)
Experimental/control comparisons of instruments.
Intercomparison at the French CESAM chamber of different instruments developed to quantify HONO (NitroMAC/LISA, IBBCEAS/LPCA and QCL absorption/PC2A).
Intercomparison of two new instruments to measure OH reactivity (FAGE and laser photolysis and Comparative Rate Method)
Ongoing studies and results
Investigation of different reaction systems: (i) equilibrium constant between the radical HO2 and CH2O as well as CH3CHO thanks to a selective detection of HO2 (ii) selective detection of CH3O2 radical by cw-CRDS and first-ever determination of the rate constant of its reaction with OH radicals: strong evidence for implication of this reaction in chemistry of remote environments, currently omitted in all major models.
Influence of the structure of hydroxyketones on their reactivity in the atmosphere: evidence for predominance of photolysis compared to their reaction with OH radicals for certain compounds.
Identification of two new pathways of formation for Criegee radicals from the ozonolysis of long chain unsaturated hydrocarbons
Study of the reactivity of several species with atmospheric interest: Isoprene, CH2O, propanal, 2-methoxyphenol, guaiacol. Special interest in the formation pathways of secondary organic aerosols (SOA)
Direct, selective in-situ detection of HO2 radicals: influence of pressure on the reaction mechanism.
Acquisition and analysis of microwave and millimetre wave spectra (i) of biogenic halogenated compound, (ii) of nopinone and its hydrates, (iii) of camphor and its hydrates, possible aerosol precursors, and (iv) of methacrolein and methyl vinyl ketone.
Measurement and quantitative analysis of high resolution IR spectra of important intermediates of the degradation of biogenic VOCs such as limonene, α- and ß-pinene glycolaldehyde, metacroleine, methyl vinyl ketone, carvone, perilaldehyde, and different isomers of methoxyphenol and syringol. Objective is to evaluate possible remote atmospheric detection of these important intermediates.
Study of the degradation mechanism of biogenic VOCs under NOx-free conditions: influence of environmental conditions on SOA formation.
Selective identification of isomers from the OH-initiated oxidation of propene.
Fate of organic gas-phase carbon during long range transport
Illustration : Correlation plot of the OH reactivity measurements from the CRM (SAGE) and pump-probe instruments (PC2A) as a function of NO mixing ratios (top) and as a function of the ratio of VOC reactivity to NOx reactivity (bottom).
Key publications
Torsion-rotation-vibration effects in the ground and first excited states of methacrolein, a major atmospheric oxidation product of isoprene, Zakharenko O. ; Motiyenko R. A. ; Aviles Moreno J.-R. ; Jabri A. ; Kleiner I. ; Huet T. R., J. Chem. Phys. 2016, 44, 024303. http://dx.doi.org/10.1063/1.4939636
Absorption cross section of OH radicals around 7028 cm‐1 and rate constant of the reaction between OH and HO2 radicals, E. Assaf, C. Fittschen, The Journal of Physical Chemistry A, 120 (36), 7051 (2016)
Intercomparison of the Comparative Reactivity Method (CRM) and Pump-Probe technique for measuring total OH reactivity in an urban environment, R. F. Hansen, M. Blocquet, C. Schoemaecker, T. Léonardis, N. Locoge, C. Fittschen, B. Hanoune, P. S. Stevens, V. Sinha, S. Dusanter, Atmospheric Measurement Technique, 8 (10), 4243 (2015)
Infrared spectroscopy of methoxyphenols involved as atmospheric secondary organic aerosol precursors: gas-phase vibrational cross-sections, A. Cuisset, C. Coeur, G. Mouret, W. Ahmad, A. Tomas, O. Pirali, Journal of Quantitative Spectroscopy and Radiative Transfer, 179, 51-58, 2016
Low pressure photolysis of 2,3-pentanedione in air: quantum yields and reaction mechanism, H. Bouzidi, M. Djehiche, T. Gierczak, P. Morajkar, C. Fittschen, P. Coddeville, A. Tomas, Journal of Physical Chemistry A, 119 (51), 12781–12789, 2015
