Experiments performed at the CLOUD aerosol chamber at CERN allow to quantify the nucleation and growth rates for chemical systems of importance for the atmosphere and to study the details of the phase transition processes at the molecular level.<br/>The chemical systems studied include (a) sulfuric acid-dimethylamine-water, (b) sulfuric acid-ammonia-water, and (c) multi-component nucleation of highly oxidized organic compounds following terpene oxidation with and without sulfuric acid. For all systems the nucleation process is studied with and without the presence of ions to determine the efficiency of ion-induced vs. neutral nucleation pathways by direct comparison. For the sulfuric acid-dimethylamine system charged and uncharged clusters containing up to dozens of molecules are detected, the temporal evolution of the molecular association steps is experimentally obtained and a complete description of the formation of clusters is derived including condensation, cluster-cluster coagulation, losses to chamber walls and dilution. This yields a quantitative description of the size dependent particle formation and growth rates at conditions relevant for the atmosphere and it is shown that the formation proceeds at the kinetic limit for this specific acid-base system.<br/>Similarly, the oxidation of α-pinene driven by peroxy radical chemistry including an efficient auto-oxidation mechanism very rapidly yields a large number of highly oxidized, extremely low volatility organic compounds (ELVOCs) and these compounds as well as their subsequent clustering reaction products are detected by use of high-resolution chemical ionization mass spectrometry. ELVOC molar yields, aerosol formation rates and growth rates for these systems are derived and their significance for contribution to atmospheric aerosol and CCN number concentrations in different regions is discussed for present day and pre-industrial conditions.

Aerosol nucleation and growth in the CLOUD experiment at CERN

249th National Meeting (2015)

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