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LABORATORY STUDIES OF NITRATE RADICAL REACTIONS OF TROPOSPHERIC IMPORTANCE.

Objective

THE NITRATE RADICAL NO3 HAS RECENTLY EMERGED AS A KEY INTERMEDIATE SPECIES IN TROPOSPHERIC CHEMISTRY. FIELD MEASUREMENTS OF NO3 BEHAVIOUR HAVE CLEARLY ESTABLISHED HOW IMPORTANT THE RADICAL IS IN CONTROLLING ATMOSPHERIC CONVERSIONS. THE OBJECTIVE OF THE PROPOSED RESEARCH IS TO PROVIDE, BY MEANS OF LABORATORY EXPERIMENTS, THE DATA REQUIRED TO UNDERSTAND THE ATMOSPHERIC CHEMISTRY OF THE NITRATE RADICAL, FROM BOTH THE MECHANISTC AND KINETIC POINTS OF VIEW. THE THREE COLLABORATING LABORATORIES OF THIS PROPOSAL ARE ALREADY MAJOR CONTRIBUTORS TO THE BODY OF DATA THAT CURRENTLY EXISTS ON THE NO3 RADICAL, AND ARE IMPORTANT AMONGST THE FEW EUROPEAN GROUPS ACTIVE IN THIS FIELD.
It has become evident that the nitrate radical, plays a significant part in the atmospehre. The nitrate radical reacts with nitrogen dioxide go give dinitrogen pentoxide which can react heterogeneously with water to yield nitric acid and thus contribute to atmospheric acidification. During the day, the nitrate radical is rapidly photolysed. At night the nitrate radical can persist. Although the hydroxyl radical is usually the main agent of attack on organic species during the day, the nitrate radical may be the most important oxidizing species in the troposphere at night.

Kinetic and mechanistic data have been obtained on nitrate on reactions, to be used in models. Most of the experimental data concern the kinetics of reactions of the nitrate radical studied by complementary techniques. A wide range of organic and inorganic reactants was studied, including radical species. One of the most important conclusions is that nitrate radical could participate in a night time chain oxidation involving peroxy radicals and generate at night.

The research has shown the potential importance of a chain volatile organic compound (VOC) oxidation mechanisms during the night. It is clear that this mechanism to be efficient requires elevated levels of nitrogen oxide and reactive organic species, simultaneously with ozone. These conditions are likely to be found in polluted coastlines, forest subject to anthropogenic pollution, urban airmasses (if ozone survives during the night), and biomass burning areas.
WORK TO BE CARRIED OUT AT OXFORD INVOLVES TWO MAIN AREAS, BOTH OF WHICH ARE OF THE GREATEST IMPORTANCE IN UNDERSTANDING ATMOSPHERIC CHEMISTRY :A) THE INTERACTION OF NO3 WITH OTHER RADICALS, MOST NOTABLY WITH HO2 AND WITH ALKYLPEROXY, RO2; B) THE THERMAL DECOMPOSITION OF NO3 IN ITS COLLISIONS WITH N2 AND O2, AND A POSSIBLE REACTION WITH OZONE. IN EACH CASE, BOTH RATE AND MECHANISTIC ASPECTS OF THE KINETICS ARE TO BE STUDIED. VARIANTS OF FLOW AND LASER FLASH PHOTOLYSIS METHODS WILL BE USED TO PROVIDE TIME RESOLUTION, AND OPTICAL ABSORPTION AND LASER INDUCED FLUORESCENCE (LIF) WILL BE EMPLOYED IN IDENTIFYING AND ESTIMATING RADICAL CONCENTRATIONS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

THE CHANCELLOR, MASTERS AND SCHOLARS OF THE UNIVERSITY OF OXFORD
Address
University Offices, Wellington Square
Oxford
United Kingdom

Participants (2)

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
France
Address
Avenue De La Recherche Scientifique 1 C
45071 Orleans
MAX-PLANCK-GESELLSCHAFT ZUR FOERDERUNG DER WISSENSCHAFTEN E.V.
Germany
Address
Johann Joachim-becher-weg 27
55020 Mainz