1. Detection of IO in the MBL using an open-path CRDS
June 25th, 2009
64th International Symposium
on Molecular Spectroscopy
Detection of IO in the MBL
using an open-path CRDS
*Ryuichi Wada, Joe M. Beames
and Andrew J. Orr-Ewing
University of Bristol, UK
* Present address: Nagoya University, Japan

2. Overview Introduction Experimental set-up
Experiments in the laboratory
Field observation
Conclusions

3. Iodine monoxide (IO) I IO OIO Aerosol Ocean I2 CH2I2 CH3I Source
Atmospheric Iodine cycle O3 n IO h I2
CH2I2
CH3I I IO
OIO
Aerosol
NO2
HO2
IONO2
HOI
Aerosol
Aerosol
Deposition
Ocean
IO is important radical to understand the chemistry in the marine boundary layer (MBL).

4. Current observation of IO
First observation of [IO]
(Mace Head, Ireland)
Observation technique
[IO] = ppt
(1ppt=1/ )
~ 20 km
Differential Optical
Absorption
Spectroscopy
(DOAS)
U. Platt and co-workers, Nature, 397, 572, 1999
DOAS is the only technique for observation of IO.
All observed [IO] were up to ~ 10 ppt.

5. There is no technique to measure inhomogeneous IO.
Disagreement with model and observation
A model for MBL prediction of [IO] = ~100 pptv
A. Ravishankara et al. Atmos. Chem. Phys., 4, 19, 2004
Possible interpretation
Inhomo- geneous
IO spot
DOAS observed average
concentration in light path
(~ 10 ppt)
Inhomogeneous sources of IO possibly exist
(~ 100 ppt)
Light path
There is no technique to measure inhomogeneous IO.

6. Cavity ring down spectroscopy
It =e-kt
Time /ms
Intensity /arb. units
It =e-k0t
∆k = k–k0
With absorbers
∆k=c[X]σX
Without absorbers
k: Ring-down decay rate
c: Speed of light
σX: Cross-section of X
High sensitivity
Optical path length ~ 10 km
Compactness
Point measurement
CRDS has a possibly to detect inhomogenious IO radicals.

7. Experimental set-up Reaction N2O + hn(193nm)→ N2 + O(1D)
YAG-Dye laser (~435 nm)
Excimer laser (193 nm)
N2O/CF3I/Ar
Reaction
N2O + hn(193nm)→ N2 + O(1D)
O(1D) + Ar → O(3P)
CF3I + O(3P) → IO + CF3
Digitiser / PC

8. IO spectra IO A2P3/2 - X2P3/2 (3,0) Simulation Rotational structure
Experiment P R
Simulation spectrum: A.Orr-Ewing et al., J. Chem. Soc. Faraday Trans., 94, 2681, 1998

9. Absorption cross-section of IO (3,0)
Experimental
Model Calculation
Numerical integration method
[CF3I]int and [N2O]int k
[IO]
Reaction kinetics of IO
N2O hn = N O(1D) O(1D) M = O(3P) + M
CF3I O(3P) = IO CF3
IO IO = Products
Wavelength
σ=5.9×10-17 cm2 molecule-1
M.Kawasaki et al., J. Phys. Chem. A, 107, 6381, 2003 • •
Time-dependent concentration of IO radicals

10. Result : time-dependent concentration of IO radicals
▪ Experimental
Model calculation
IO + IO → Product
[IO] is good agreement between experiment and model.

11. Simulate the absorption cross-section IO A2P3/2 - X2P3/2 (3,0)
Resolution
0.2 cm-1
24 cm-1
Kawasaki et al.,
J. Phys. Chem. A, 2003
5.9 ± 0.6
3.1±0.4
Harwood et al., J. Phys. Chem. A, 1997 -
2.7±0.4
convolution
Unit: cm2 molecule-1
Simulated spectrum
Resolution: cm-1
- 24 cm-1

12. Open-path CRD spectrometer
Detector
YAG-Dye laser system
HR mirror
Optical table
Sampling Air
Electronics
Wheel & Vibration isolator

13. Field observation in Roscoff
High tide
Low tide
Extensive Seaweed beds are exposed.

14. Measurements method Total accumulation time for one data point: 30 s
Bandhead IO 6
Total accumulation time
for one data point: 30 s 4
/ cm2 molecule-1
Cross-section of IO 2
Baseline
22944
22948
22952
22956
Wavenumber /cm-1
NO2
NO2 has absorption in the measurement wavenumbers. 6
/10-19 cm2 molecule-1
Cross-section of NO2
/ cm2 molecule-1 4
Same value of cross-sections 2
No interferences of NO2
22944
22948
22952
22956
Wavenumber /cm-1

15. Observation results 25th September 2006
Fine & cloudy day
● Mixing ratio of IO
○ Minimum detectable limit
Wind
High [IO] radicals were successfully detected.
The concentrations have inverse-trend with tidal heights.

16. Conclusions
An open-path CRD spectrometer was designed and constructed for atmospheric IO radicals.
The cross-section of IO was tested by both of kinetic measurement and model simulation.
3. The open-path CRD spectrometer had been deployed in the field campaign and successfully detected high concentration of IO radicals.

17. Acknowledgements Professor Andrew J. Orr-Ewing
Dr Gordon McFiggans and observation team in RHaMBLe projects
Professor Yutaka Matsumi
Funding:
EPSRC
STE research lab in Nagoya University