HR: 0800h
AN: A51C-0579    [Abstracts]
TI: Development and Deployment of a Field Instrument for the Detection of Iodine Atoms Using Resonance Fluorescence
AU: * Bale, C S
EM: c.s.e.bale@leeds.ac.uk
AF: University of Leeds, School of Chemistry Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Ingham, T
EM: t.ingham@leeds.ac.uk
AF: University of Leeds, School of Chemistry Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Commane, R
EM: r.commane05@leeds.ac.uk
AF: University of Leeds, School of Chemistry Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Heard, D E
EM: d.e.heard@leeds.ac.uk
AF: University of Leeds, School of Chemistry Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Bloss, W J
EM: w.j.bloss@bham.ac.uk
AF: University of Birmingham, School of Geography Earth and Environmental Sciences, Birmingham, B15 2TT, United Kingdom
AB: Recently there have been several measurements of I₂, alkyl iodides (CH₃I, CH₂I₂), iodine monoxide (IO) and OIO at sites including coastal, polar and open ocean environments. I₂ and the alkyl iodides are rapidly photolysed in the atmosphere to liberate iodine atoms which may then react with ozone to form iodine monoxide (IO) radicals. Subsequent reactions of IO lead to the catalytic depletion of tropospheric ozone, affect OH:HO₂ and NO:NO₂ ratios, oxidise dimethyl sulphide and result in the formation of new particles. While the IO radical and its stable precursors have previously been detected and measured in the marine boundary layer, little is known about the levels of reactive inorganic halogen species, or the local distribution of iodine activity at coastal sites such as Mace Head (Ireland). We have developed an instrument which employs vacuum UV resonance-fluorescence using a microwave discharge lamp to detect atomic iodine via the (5p⁵) \ ²P_3/2 ← \ ²P_3/2 \ (6s¹) transition near 178 nm. The instrument is calibrated by generating a known concentration of iodine atoms from the photolysis of I₂ at 185 nm. The system can be operated in two modes; either to measure ambient iodine atoms (in photochemical steady state with their precursors and IO), or to measure the total photolabile iodine loading, through broadband visible photolysis of ambient air, with detection of the iodine atoms formed. This technique allows for the in-situ measurement of the species detected, which is advantageous for gathering information about their local distribution and source. The instrument was deployed for the first time in August 2007 at Mace Head on the west coast of Ireland. We present initial results from this field trial, which represent the first observation of ambient iodine atoms in the marine atmosphere. The results will be compared with the measurements of IO obtained from the University of Leeds laser-induced fluorescence (LIF) instrument.
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting