To study the kinetic and physical processes involved in the reactions of nitrogen oxides and halogen species in the marine boundary

The project "SALT" is designed to investigate the heterogeneous mechanisms and origin of the high concentrations of halogenated reservoir species and free radicals (especially brominated radicals) recently observed in the marine boundary layer. The presence of halogen species is expected to greatly influence the oxidising capacity of the troposphere, and it is of major importance to investigate the kinetics and mechanism of halogen release from sea-salt.
This project is therefore dedicated to laboratory studies of heterogeneous reactions of both nitrogen oxides (NOy) and halogen reservoirs occurring in or at the surface of sea-salt aerosols and which release photo-labile precursors of halogenated radicals.
The objectives can be summarised as:
.Identification of the primary products from the reactions of NOy and HOX with liquid and frozen salt solutions and with dry salts. Conditions will be chosen to mimic atmospheric materials, i.e. the influence of chloride and bromide will be investigated;
.Study of the kinetics and physical processes involved in the uptake rates of NOy and of the inorganic halogenated products by the materials noted above. It is now postulated that the products could exist in the form of nitryl halides XNO2 (or, possible but not likely, their isomers XONO) or other halogen containing compounds (X2, HOX,..) These studies will be undertaken using the presently most powerful tools available in the field of heterogeneous atmospheric chemistry, i.e. droplet train technique, wetted-wall flowtubes and Knudsen cell reactors, enabling coverage of the different regimes that may occur in the troposphere. These techniques will be coupled with complementary analytical methods including mass spectrometry (quadrupole, ion-trap and time of flight), optical techniques such as laser induced fluorescence (LIF), resonance enhanced multi photon ionisation (REMPI), Fourier transform infra-red spectroscopy (FTIR), electron spin resonance (ESR) and finally, chromatographic liquid phase analysis (HPLC, IC). This large pallet of analytical methods will allow identification of most of the products involved in this chemistry.
The outcome of this project will be substantial improvement of our knowledge of the heterogeneous chemistry of sea-salt aerosols in the troposphere. Combined with photochemical models, this will enable improved determination of the source strength and fate of halogen containing free-radicals resulting from gas/liquid reactions.
Keywords:
Heterogeneous reactions, halogen activation, active chlorine and bromine, sea-salt aerosols, heterogeneous nitrogen oxide chemistry, droplet train technique, heterogeneous flowtube reactor, Knudsen cell reactor.
The project "SALT" is designed to investigate the heterogeneous mechanisms and origin of the high concentrations of halogenated reservoir species and free radicals (especially brominated radicals) recently observed in the marine boundary layer. The presence of halogen species is expected to greatly influence the oxidising capacity of the troposphere, and it is of major importance to investigate the kinetics and mechanism of halogen release from sea-salt.
This project is therefore dedicated to laboratory studies of heterogeneous reactions of both nitrogen oxides (NOy) and halogen reservoirs occurring in or at the surface of sea-salt aerosols and which release photo-labile precursors of halogenated radicals. The influence of chloride and bromide in the reactions of NOy and HOX with liquid and frozen salt solutions will be investigated.
These studies will be undertaken using the presently most powerful tools available in the field of heterogeneous atmospheric chemistry, i.e. droplet train technique, wetted-wall flowtubes and Knudsen cell reactors, enabling coverage of the different regimes that may occur in the troposphere. These techniques will be coupled with complementary analytical methods including mass spectrometry (quadrupole, ion-trap and time of flight), optical techniques such as laser induced fluorescence (LIF), resonance enhanced multi photon ionisation (REMPI), Fourier transform infra-red spectroscopy (FTIR), electron spin resonance (ESR) and finally, chromatographic liquid phase analysis (HPLC, IC). This large pallet of analytical methods will allow identification of most of the products involved in this chemistry.
The outcome of this project will be substantial improvement of our knowledge of the heterogeneous chemistry of sea-salt aerosols in the troposphere. Combined with photochemical models, this will enable improved determination of the source strength and fate of halogen containing free-radicals resulting from gas/liquid