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Marine aerosol formation from biogenic iodine emissions


The formation of marine aerosols and cloud condensation nuclei—from which marine clouds originate—depends ultimately on the availability of new, nanometre-scale particles in the marine boundary layer. Because marine aerosols and clouds scatter incoming radiation and contribute a cooling effect to the Earth's radiation budget1, new particle production is important in climate regulation. It has been suggested that sulphuric acid—derived from the oxidation of dimethyl sulphide—is responsible for the production of marine aerosols and cloud condensation nuclei. It was accordingly proposed that algae producing dimethyl sulphide play a role in climate regulation2, but this has been difficult to prove and, consequently, the processes controlling marine particle formation remains largely undetermined3,4. Here, using smog chamber experiments under coastal atmospheric conditions, we demonstrate that new particles can form from condensable iodine-containing vapours, which are the photolysis products of biogenic iodocarbons emitted from marine algae. Moreover, we illustrate, using aerosol formation models, that concentrations of condensable iodine-containing vapours over the open ocean are sufficient to influence marine particle formation. We suggest therefore that marine iodocarbon emissions have a potentially significant effect on global radiative forcing.

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Figure 1: Observed aerosol mass spectrum from chamber experiments as measured by the aerosol mass spectrometer.
Figure 2: Chemical pathway from CH2I2 to aerosol production, on the basis of the current state of knowledge of the gas-phase chemistry.
Figure 3: Model simulations of condensable vapour and aerosol concentrations in the marine boundary layer.
Figure 4: Initial (local time 06:00) and predicted final (local time 20:00) aerosol size distributions for CIV source rates (Q) of 0, 103, 5 × 103, 10 × 103 and 25 × 103 molecules cm-3 s-1.


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This work was funded by the European Commission, the Finnish Academy, the US Department of Energy and the National Development Plan and Environmental Protection Agency, Ireland.

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Correspondence to Colin D. O'Dowd.

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O'Dowd, C., Jimenez, J., Bahreini, R. et al. Marine aerosol formation from biogenic iodine emissions. Nature 417, 632–636 (2002).

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