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Content archived on 2024-04-16

Heterogenous and homogenous chemistry ClOy, BrOy and NOy compounds on polarstratospheric cloud mimics


The aim of this project is to obtain a quantitative understanding of the products, mechanisms and kinetics of reactions associated with the low temperature polar stratospheric cloud(PSC) surface chemistry of various chlorine and bromine species, nitrogen oxide compounds and ozone. This information is required to clarify aspects of heterogeneous and homogeneous stratospheric chemistry, which have been shown to be important in determining observed annual depletion in ozone levels over Antarctica.

It is now widely believed that much of the heterogeneous chemistry which accounts for the conversion of reservoir chlorine oxide to reactive chlorine oxide species and also reactive nitrogen oxide to reservoir nitrogen oxide species occurs within polar stratospheric clouds (PSC). The low temperature particles implicated in these chemical transformations are of 2 main types: formed at around 195 K consisting of nitric acid trihydrate (NAT) with diameters 0.2 to 0.5 um; and formed at temperatures <188 K consisting of a NAT nucleus but surrounded by water and ice to give overall diameters 10 to 20 um. If it is accepted that the observed chemistry is solely associated with the surface grain boundaries of such particles, then the use of an extended 2 dimensional surface several mm{2} in total area will represent a suitable mimic for laboratory studies of PSC behaviour.

The specific research objectives are as follows.
Characterization of nitric acid ice and water ice PSC mimics using Fourier transform infrared(FTIR) and laser induced fluorescence(LIF) to determine related absorption cross sections in the ultraviolet(UV).
Determination of PSC surface reaction products and mechanisms using FTIR, LIF, mass spectrometry(MS) and resonance enhanced multiphoton ionization(REMPI).
Determination of sticking coefficients for chlorine oxide, bromine oxide and nitrogen oxide on ice surfaces at different temperatures using FTIR and MS.
Determination of gas phase products of bromine oxide chemistry and laser photochemistry using cryogenic techniques and FTIR.
Determination of the effect of photolysis on PSC mimics. This will serve as a useful preliminary to a study of PSC photochemical surface reactions.


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University Plain Norwich Research Park
United Kingdom

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Participants (3)