|
The graph below shows the concentration of iodine in several aerosol samples collected at Weybourne. Line 1 represents the total amount of iodine in the samples and lines 2 and 3 represent how much of the total can be extracted into water as inorganic iodine at different temperatures (95°C for line 2, 20°C for line 3). We believe that the graph shows the presence of some insoluble iodine (the difference between lines 1 and 2), and some soluble organic iodine compounds (the high temperature used for line 2 breaks these down, but this does not happen for line 3). See Baker et al., 2000 for more details.
|
| The inorganic forms of iodine represented in line 3 of the graph above are iodide (I-) and iodate (IO3-). By examining some other samples from our work at Weybourne we have been able to show that the production of iodate is rather slow, in terms of the lifetime of the aerosol particles. This is significant because iodate cannot escape from the aerosol and get back into the air. While aerosol iodine is in the form of iodide, it may be able to leave the aerosol and resume ozone destruction reactions in the atmosphere. (see Baker et al., 2001). |
| |
| Iodine speciation in aerosol collected over the tropical Atlantic Ocean has shown some interesting and surprising differences between the northern and southern hemispheres. The boundary between the hemispheres is known as the Intertropical Converge Zone (ITCZ) and this zone migrates seasonally through the tropics. In the Atlantic the ITCZ normally moves between the equator and 10°N. Below is the cruise track of the RV Meteor (Cruise M55) in October / November 2002 with periods of time when the ship was moving through southern hemisphere air shaded in grey. |
|
| Overall the concentration of iodate in the aerosol samples collected during M55 was 5-fold higher than the concentraiton of iodide. In the southern hemisphere however iodate could not be detected at all - a very unexpected result indeed. At present we do not know what controls this dramatic shift in iodine chemistry. (See Baker, 2004). |
References
| A.R. Baker. (2005). Marine aerosol iodine chemistry: The importance of soluble organic iodine, Environmental Chemistry, 2, 295-298. |
| A.R. Baker. (2004). Inorganic iodine speciation in tropical Atlantic aerosol, Geophysical Research Letters, 31, L23S02, doi:10.1029/2004GL020144. |
| A.R. Baker, C. Tunnicliffe, T.D. Jickells. (2001). Iodine speciation and deposition fluxes from the marine atmosphere, Journal of Geophysical Research - Atmospheres, 106, 28743-28749. |
| A.R. Baker, D. Thompson, M.L.A.M. Campos, S.J. Parry, T.D. Jickells. (2000). Iodine concentration and availability in atmospheric aerosol, Atmospheric Environment, 34, 4331-4336. |
This page was last updated in February 2007. |
