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SUMMARY:Laboratory studies of halogen oxide radical reactions and sensor  
 development for reactive gases  - Dr Valerio Ferracci\, Cambridge Universi
 ty
DTSTART:20160201T141500Z
DTEND:20160201T151500Z
UID:TALK64114@talks.cam.ac.uk
CONTACT:Paul Griffiths
DESCRIPTION:ur knowledge of the composition of the atmosphere and our unde
 rstanding \nof its chemistry relies on the synergistic efforts of field \n
 measurements\, atmospheric modelling and laboratory studies: any attempt \
 nto replicate field observations by means of modelling requires accurate \
 ncharacterisation of the kinetics and photochemistry of atmospheric \nproc
 esses. This seminar focuses on the measurement aspects of \natmospheric sc
 ience by presenting laboratory studies of halogen oxide \nreactions implic
 ated in ozone depletion along with the development of a \nsensor for ambie
 nt ammonia underpinned by novel primary gas standards. \n\nThe self- and c
 ross-reactions of halogen oxide radicals are complex \nmultichannel proces
 ses\, with both bimolecular and termolecular \ncomponents contributing to 
 the overall reaction\; as some product \nchannels do not contribute to the
  catalytic destruction of ozone\, an \naccurate determination of the produ
 ct branching is of utmost importance \nfor a comprehensive understanding o
 f the atmospheric ozone budget. \nKinetic results for the ClO and BrO self
 -reactions and the BrO + ClO \ncross-reaction are presented. These were st
 udied by means of laser \nphotolysis coupled with UV absorption spectrosco
 py with charge-coupled \ndevice (CCD) detection which allowed broadband ti
 me-resolved acquisition \nof spectra\, leading to the unequivocal identifi
 cation of multiple \nspecies and to the accurate quantification of their c
 oncentrations. The \nfindings are compared with previous studies and their
  implications are \ndiscussed. \n\nIt is estimated that by 2020 ammonia wi
 ll be main source of \nacidification\, eutrophication and secondary aeroso
 l formation in Europe \nas a result of intensive farming and the use of ni
 trogen-based \nfertilisers. Accurate measurements of ambient ammonia are n
 eeded to \nverify the impact of environmental policies\, as well as to min
 imise \nuncertainties in emissions inventories and to provide independent 
 \nverification of atmospheric model predictions. However state-of-the-art 
 \nmethods currently used in the field suffer from a number of drawbacks\, 
 \nincluding low accuracy and poor temporal resolution and also require \nc
 omplex post-exposure analysis. The further development of an optical \nsen
 sor based on cavity ring-down spectroscopy (CRDS)\, underpinned by \nprima
 ry ammonia reference standards\, is described\, with a view to \nextending
  this rapid on-line technique for exposure chamber validation \ntests unde
 r controlled conditions and ambient monitoring in the field. \n
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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