Ozone depletion due to dust release of iodine in the free troposphere
Iodine is an atmospheric trace element emitted from oceans that efficiently destroys ozone (O 3 ). Low O 3 in airborne dust layers is frequently observed but poorly understood. We show that dust is a source of gas-phase iodine, indicated by aircraft observations of iodine monoxide (IO) radicals inside lofted dust layers from the Atacama and Sechura Deserts that are up to a factor of 10 enhanced over background. Gas-phase iodine photochemistry, commensurate with observed IO, is needed to explain the low O 3 inside these dust layers (below 15 ppbv; up to 75% depleted). The added dust iodine can explain decreases in O 3 of 8% regionally and affects surface air quality. Our data suggest that iodate reduction to form volatile iodine species is a missing process in the geochemical iodine cycle and presents an unrecognized aeolian source of iodine. Atmospheric iodine has tripled since 1950 and affects ozone layer recovery and particle formation.
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NSF-PAR ID:
10349978
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Volume:
7
Issue:
52
ISSN:
2375-2548
4. Abstract. Photoacoustic spectroscopy (PAS) has become a popular technique for measuringabsorption of light by atmospheric aerosols in both the laboratory andfield campaigns. It has low detection limits, measures suspended aerosols,and is insensitive to scattering. But PAS requires rigorous calibration to beapplied quantitatively. Often, a PAS instrument is either filled with a gasof known concentration and absorption cross section, such that the absorptionin the cell can be calculated from the product of the two, or the absorptionis measured independently with a technique such as cavity ring-downspectroscopy. Then, the PAS signal can be regressed upon the known absorptionto determine a calibration slope that reflects the sensitivity constant ofthe cell and microphone. Ozone has been used for calibrating PAS instrumentsdue to its well-known UV–visible absorption spectrum and the ease with whichit can be generated. However, it is known to photodissociate up toapproximately 1120nm via the O3 + $h\mathit{\nu }\phantom{\rule{0.25em}{0ex}}\left(>\mathrm{1.1}\mathrm{eV}\right)\to {\mathrm{O}}_{\mathrm{2}}{\left(}^{\mathrm{3}}{\mathrm{\Sigma }}_{g}^{-}\right)$ + O(3P) pathway, which is likely tolead to inaccuracies in aerosol measurements. Two recent studies haveinvestigated the use of O3 for PASmore »