On the Importance of Organic Mass for Global Cloud Condensation Nuclei Distributions
Aerosol-cloud interactions constitute a major contributor of uncertainty in projections of anthropogenic climate change. The fraction of aerosol that activates to form cloud droplets (cloud condensation nuclei, CCN) is at the heart of aerosol cloud interactions. Towards this, we investigate the role of organic mass in the formation and evolution of CCN using the global 3-dimensional chemistry transport model TM4-ECPL coupled with the M7 aerosol microphysics module. The contribution of organics to the CCN levels is quantified by comparing the global surface distribution of aerosol particles and CCN computed with and without organic aerosol mass considerations, to the surface CCN observations. We also calculate the dynamical behavior of the CCN by computing their persistence times in atmosphere, i.e. the period over which the CCN concentrations show autocorrelation. It is found that organic species in aerosol modulate CCN concentrations by 50–90%—with a higher influence over land; furthermore, simulations compare better with observations when the impact of organics on CCN levels is taken into account.
This work has been supported by the European FP7 collaborative project BACCHUS (Impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding. We acknowledge use of the ACTRIS database provided by Schmale, J. and co-workers.
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