HR: 11:05h
AN: A42B-04 [Abstracts]
TI: In situ IO Measurements in the Marine Boundary Layer Using Laser-Induced Fluorescence Spectroscopy
AU: Heard, D E
EM: D.E.Heard@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Bale, C S
EM: C.S.E.Bale@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Bloss, W J
EM: W.J.Bloss@bham.ac.uk
AF: School of Geography, Earth and Environmental Sciences, University of Birmingham,
Birmingham, B15 2TT, United Kingdom
AU: * Commane, R
EM: chmrco@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Furneaux, K L
EM: chmklf@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Ingham, T
EM: T.Ingham@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Whalley, L K
EM: L.K.Whalley@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
AB:
The iodine monoxide (IO) radical plays an important role in the chemistry of the marine boundary layer (MBL). It is
formed by the reaction of ozone with iodine atoms generated by the photolysis of I2 and photo-labile
iodocarbons and at night from the reaction of NO3 with I2 and O3. IO is implicated in ozone
destruction, DMS oxidation and new particle formation. IO has been measured previously using LP-DOAS, with
absorption paths of several kilometres, and MAX-DOAS both of which are associated with significant spatial
averaging over the halogen source regions.
An in situ laser-induced fluorescence (LIF) technique has been developed to detect {IO} radicals in the MBL
(Whalley et. al. (2007), J. Atmos. Chem. 58: 19 - 39) and has been employed in two separate instruments.
In both field instruments, an all solid-state pulsed laser operating at 445 nm is used to excite IO in the A 2
Π3/2 \ (ν'=2) \ ← \ X 2 Π3/2 \ (ν"=0) electronic transition, with off-resonant fluorescence
detected at 520.3 nm in the (2,5) band. The sensitivity of each instrument is determined by the generation of
known concentrations of IO (between 5 and 100 pptv) from the photolysis of N2O at 185 nm followed by the
subsequent reaction of oxygen atoms with CF3I.
The first instrument was deployed in Roscoff, North-western France during August/September 2006 as part of the
RHaMBLe (Reactive Halogens in the Marine Boundary Layer) campaign. The instrument limit of detection was
0.4 pptv for a 5 min integration time, with an uncertainty of 23%. Located on a small jetty, the instrument
measured significant levels of IO on 11 days, with up to 29 pptv observed (10 second average). IO displayed a
clear diurnal profile with a maximum at low tide, and lower concentrations observed on some nights. This is
compared with LP-DOAS (University of Leeds) measurements also made at the site.
The second instrument was deployed twice in 2007. The instrumental limit of detection was also found to be 0.4
pptv for a 5 minute integration time, with an overall uncertainty of 23%. The first deployment was aboard the
RSS Discovery to measure open ocean IO over the Mauritanian upwelling during May/June 2007. The second
deployment was to Mace Head, Western Ireland during August 2007. At Mace Head, IO was observed on all 9
measurement days, with a maximum of 28 pptv observed (1 min average) coinciding with low (spring) tide.
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting