Global modeling of tropospheric iodine aerosol

Natural 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

Natural aerosol direct and indirect radiative effects

Natural aerosol plays a significant role in the Earth's system due to its ability to alter the radiative balance of the Earth. Here we use a global aerosol microphysics model together with a radiative transfer model to estimate radiative effects for five natural aerosol sources in the present-day atmosphere: dimethyl sulfide (DMS), sea-salt, volcanoes, monoterpenes, and wildfires. We calculate large annual global mean aerosol direct and cloud albedo effects especially for DMS-derived sulfate (-0.23 Wm and -0.76 Wm, respectively), volcanic sulfate (-0.21 Wm and -0.61 Wm) and sea-salt (-0.44 Wm and -0.04 Wm ). The cloud albedo effect responds nonlinearly to changes in emission source strengths. The natural sources have both markedly different radiative efficiencies and indirect/direct radiative effect ratios. Aerosol sources that contribute a large number of small particles (DMS-derived and volcanic sulfate) are highly effective at influencing cloud albedo per unit of aerosol mass burden. Key Points New, consistent estimates of natural aerosol radiative effects are given We find substantial variability in natural aerosol radiative efficiency Non-linear sensitivity of cloud albedo effects to emission source strength

Transport of tropospheric ozone and precursors to the Arctic: lessons from a multi-model evaluation using aircraft, satellite and surface data

International audienceChanges in abundances of short-lived climate pollutants such as tropospheric ozone and aerosol may have contributed significantly to observed rapid Arctic warming in recent decades. Ozone in the Arctic troposphere is influenced by long-range transport of polluted air from Europe, Asia and N. America, and in summer from boreal wildfires. Our understanding of how different sources contribute to Arctic tropospheric ozone is limited, and is reliant on sparse observations and models of atmospheric transport and chemistry. In particular, our confidence in future high latitude tropospheric ozone response to projected changes in mid-latitude emissions, and subsequent climate impacts, is informed by the ability of models to accurately simulate poleward export from source regions, long-range transport to high latitudes, and photochemical transformation of ozone and its precursors during such events