Kinetic nucleation and ions in boreal forest particle formation events

[摘要] In order to gain a more comprehensive picture on different mechanisms behindatmospheric particle formation, measurement results from QUEST 2-campaignare analyzed with an aid of an aerosol dynamic model. A special emphasisis laid on air ion and charged aerosol dynamics. Model simulations indicatethat kinetic nucleation of ammonia and sulphuric acid together withcondensation of sulphuric acid and low-volatile organic vapours ontoclusters and particles explain basic features of particleformation events as well as ion characteristics. However,an observed excess of negative ions in the diameter range 1.5-3nmand overcharge of 3-5nm particles demonstrate that ions are also involvedin particle formation. These observations can be explained bypreferential condensation of sulphuric acidonto negatively charged clusters and particlesand/or contribution of ion-induced nucleation on particle formation.According to model simulations, which assume that the nucleationrate is equal to the sulfuric acid collision rate, the relative contribution of ion-basedparticle formation seems to be smaller than kinetic nucleation of neutral clusters.Conducted model simulations also corroborate the recently-presented hypothesis accordingto which a large number of so-calledthermodynamically stable clusters (TSCs) having a diameter between 1-3nmexist in the atmosphere. TSCs were found to grow to observable sizesonly under favorable conditions, e.g. when the pre-existing particleconcentration was low.

[学科分类] 大气科学