Abstract
AbstractNatural aerosols play a central role in the Earth system. The conversion of dimethyl sulfide to sulfuric acid is the dominant source of oceanic secondary aerosol. Ocean emitted iodine can also produce aerosol. Using a GEOS‐Chem model, we present a simulation of iodine aerosol. The simulation compares well with the limited observational data set. Iodine aerosol concentrations are highest in the tropical marine boundary layer (MBL) averaging 5.2 ng (I) m−3 with monthly maximum concentrations of 90 ng (I) m−3. These masses are small compared to sulfate (0.75% of MBL burden, up to 11% regionally) but are more significant compared to dimethyl sulfide sourced sulfate (3% of the MBL burden, up to 101% regionally). In the preindustrial, iodine aerosol makes up 0.88% of the MBL burden sulfate mass and regionally up to 21%. Iodine aerosol may be an important regional mechanism for ocean‐atmosphere interaction.
Highlights
Atmospheric aerosols are important for climate as they scatter solar radiation and change cloud properties, with secondary aerosols playing a significant role [Stocker et al, 2000]
Iodine aerosol makes up 0.88% of the marine boundary layer (MBL) burden sulfate mass and regionally up to 21%
The oceans cover most of the planet, and for the last four decades the most important oceanic secondary source of aerosols has been thought to be the emission of dimethyl sulfide (DMS) and its oxidation to H2SO4 [Lovelock et al, 1972; Fitzgerald, 1991]
Summary
Atmospheric aerosols are important for climate as they scatter solar radiation and change cloud properties, with secondary aerosols playing a significant role [Stocker et al, 2000]. Recent evidence for significant emissions of iodine from the ocean [Carpenter et al, 2013; MacDonald et al, 2014], coupled to previous coastal studies of iodine aerosol production [O’Dowd et al, 2002], suggests the potential for an additional ocean aerosol source from iodine. Oceanic emissions of methyl iodide were considered the dominant source for many years, but studies have shown that emission of other iodinated hydrocarbons from the open and coastal ocean play an important role [Jones et al, 2010; Saiz-Lopez et al, 2012a]. Inorganic iodine compounds (I2, HOI) produced in the ocean surface layer from the reaction of O3 with iodide are thought to be the dominant global source of iodine [Carpenter et al, 2013]. We describe simulations of tropospheric iodine aerosol within the GEOS-Chem chemical transport model, compare the calculated iodine masses against observations, and evaluate its impact as a source of secondary aerosol for the present day and preindustrial
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