A new aerosol dynamics model (DMANx) has been developed that simulatesaerosol size/composition distribution and includes the condensation oforganic vapors on nanoparticles through the implementation of the recentlydeveloped volatility basis set framework. Simulations were performed forHyytiälä (Finland) and Finokalia (Greece), two locations with differentorganic sources where detailed measurements were available to constrain thenew model. We investigate the effect of condensation of organics and chemicalaging reactions of secondary organic aerosol (SOA) precursors on ultrafineparticle growth and particle number concentration during a typical springtimenucleation event in both locations. This work highlights the importance ofthe pathways of oxidation of biogenic volatile organic compounds and theproduction of extremely low volatility organics. At Hyytiälä, organiccondensation dominates the growth process of new particles. Thelow-volatility SOA contributes to particle growth during the early growthstage, but after a few hours most of the growth is due to semi-volatile SOA.At Finokalia, simulations show that organics have a complementary role in newparticle growth, contributing 45% to the total mass of new particles.Condensation of organics increases the number concentration of particles thatcan act as CCN (cloud condensation nuclei) () by 13% at Finokaliaand 25% at Hyytiälä during a typical spring day with nucleation. Thesensitivity of our results to the surface tension used is discussed.
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