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THE INFLUENCE OF ATLANTIC AIR MASSES ON OXIDATION PROCESSES OVER WESTERN EUROPE (OCEANO NOX PROJECT).

Ziel

TO ELUCIDATE THE CHEMISTRY OF TRACE GASES IN MARINE ATMOSPHERE.
The OCEANO-NOX project was carried out in order to attain better comprehension of the chemical processes occurring in Atlantic air masses advecting over large regions of Western Europe.

The photochemistry of iodine containing compounds in the marine boundary layer was studied. It is now possible to describe the gas phase transformations of iodine with some confidence. Calculations to investigate the influence of these transformations on the chemistry of the marine boundary layer have been carried out using a simple box model.

Daytime dimethyl sulphide (DMS) oxidation studies established that the reaction of iodine oxide with DMS is not important for marine chemistry. Data and observations indicate that nitrogen oxide concentration is a critical parameter in determining the sulphur dioxide methanesulphonic acid branching ratio in the oxidation of DMS.

The nitrate free radical in the marine troposphere was studied with respect to vertical concentration gradient and reaction with DMS. The lifetime of nitrate was determined from simultaneous measured concentrations of nitrate, nitrogen dioxide and ozone using differential optical absorption spectroscopy (DOAS).

It was concluded that at a coastal site the nitrate DMS reaction can be the dominant factor controlling the lifetime of nitrate radicals.

A study of peroxy radicals produced at night involving nitrate DMS interaction (in the marine boundary layer) showed that atmospheric conditions exist, where peroxy radicals concentrations can be elevated, possibly even exceeding daytime values. The perequisite for this phenomenom is the simultaneous presence of reactive organic species, nitrogen oxide and ozone in the same air mass.

The chemical behaviour of nonmethane hydrocarbons in the marine boundary layer was examined. Significant variations of the nonmethane hydrocarbons mixing ratios have been observed as a function of origin of air masses. In the presence of maritime air masses, low levels of alkanes and alkenes were observed. Much higher levels were measured when continental air masses advected over the site.
THE RESEARCH PROJECT IS IMPLEMENTED BY MEANS OF LABORATORY KINETIC DATA AND MEASUREMENTS OF SPECIES CONCENTRATIONS OF RELEVANCE TO THE OXIDATION OF SULPHUR AND NITROGEN COMPOUNDS IN AIR MASSES OF MARIN ORIGIN WHICH INFLUENCE THE COMPOSITION OF AIR OVER THE CONTINENT.
OXIDATION PROCESSES INVOLVING REACTIONS OF HOX, NOX AND HALOGEN SPECIES (BR, CL, I) WITH VOLATILE ORGANIC COMPOUNDS AND DMS ARE CONSIDERED IN ORDER TO OBTAIN THE RATE CONSTANTS AND ELUCIDATE THE MECHANISMS OF THE COMPLEX REACTION SYSTEMS.

THE WORK INVOLVES THE COMPLEMENTARY STUDIES OF SIX LABORATORIES : CNRS ORLEANS AND GIF-SUR YVETTE, UNIVERSITY PARIS VII, UKAEA HARWELL, KFA JUELICH AND UNIVERSITY OF WUPPERTAL.

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Centre National de la Recherche Scientifique (CNRS)
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