Abstract
Abstract. The first in situ point observations of iodine monoxide (IO) at a clean marine site were made using a laser-induced fluorescence instrument deployed at Mace Head, Ireland in August 2007. IO mixing ratios of up to 49.8 pptv (equivalent to pmol mol−1; 1 s average) were observed at day-time low tide, well in excess of previous observed spatially-averaged maxima. A strong anti-correlation of IO mixing ratios with tide height was evident and the high time resolution of the observations showed IO peaked in the hour after low tide. The temporal delay in peak IO compared to low tide has not been observed previously but coincides with the time of peak aerosol number previously observed at Mace Head. A long path-differential optical absorption spectroscopy instrument (with a 2 × 6.8 km folded path across Roundstone Bay) was also based at the site for 3 days during the point measurement observation period. Both instruments show similar temporal trends but the point measurements of IO are a factor of ~6–10 times greater than the spatially averaged IO mixing ratios, providing direct empirical evidence of the presence of inhomogeneities in the IO mixing ratio near the intertidal region.
Highlights
The important role of iodine chemistry in the marine boundary layer has been highlighted by a number of studies (e.g., Alicke et al, 1999; Read et al, 2008; O’Dowd et al, 2002)
We present point observations of iodine monoxide (IO) made using a portable and compact Laser-Induced Fluorescence (LIF) instrument developed for the detection of IO
It was found that no response in signal above the calculated instrumental limit of detection (LOD) was observed for NO2 mixing ratios below 500 ppbv, which is far less than the sub-ppbv levels of NO2 observed at clean marine sites
Summary
The important role of iodine chemistry in the marine boundary layer has been highlighted by a number of studies (e.g., Alicke et al, 1999; Read et al, 2008; O’Dowd et al, 2002). The iodine monoxide (IO) radical is involved in the catalytic destruction of ozone in the marine boundary layer (Davis et al, 1996) This destruction can be initiated by the reaction of IO with itself or BrO as well as with the HO2 radical or NO2. Recent laboratory work suggests that IO and OIO react to form higher oxides I2O3 and I2O4, which polymerise and grow to ultrafine particles (Saunders et al, 2010). If these new particles grow to form cloud condensation nuclei (CCN), they can influence cloud properties and have an impact on climate (Rosenfeld et al, 2008).
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