title: Toward direct measurement of atmospheric nucleation.
abstract: Atmospheric aerosol formation is known to occur almost all over the world, and the importance of these particles to climate and air quality has been recognized. Although almost all of the processes driving aerosol formation take place below a particle diameter of 3 nanometers, observations cover only larger particles. We introduce an instrumental setup to measure atmospheric concentrations of both neutral and charged nanometer-sized clusters. By applying the instruments in the field, we come to three important conclusions: (i) A pool of numerous neutral clusters in the sub-3 nanometer size range is continuously present; (ii) the processes initiating atmospheric aerosol formation start from particle sizes of approximately 1.5 nanometers; and (iii) neutral nucleation dominates over the ion-induced mechanism, at least in boreal forest conditions.
authors.affiliation: Department of Physical Sciences, University of Helsinki, Post Office Box 64, FI-00014, Helsinki, Finland. kulmala@pcu.helsinki.fi
authors.forename: Markku
authors.initials: M
authors.lastname: Kulmala
authors.forename: Ilona
authors.initials: I
authors.lastname: Riipinen
authors.forename: Mikko
authors.initials: M
authors.lastname: Sipilä
authors.forename: Hanna E
authors.initials: HE
authors.lastname: Manninen
authors.forename: Tuukka
authors.initials: T
authors.lastname: Petäjä
authors.forename: Heikki
authors.initials: H
authors.lastname: Junninen
authors.forename: Miikka Dal
authors.initials: MD
authors.lastname: Maso
authors.forename: Genrik
authors.initials: G
authors.lastname: Mordas
authors.forename: Aadu
authors.initials: A
authors.lastname: Mirme
authors.forename: Marko
authors.initials: M
authors.lastname: Vana
authors.forename: Anne
authors.initials: A
authors.lastname: Hirsikko
authors.forename: Lauri
authors.initials: L
authors.lastname: Laakso
authors.forename: Roy M
authors.initials: RM
authors.lastname: Harrison
authors.forename: Ian
authors.initials: I
authors.lastname: Hanson
authors.forename: Carl
authors.initials: C
authors.lastname: Leung
authors.forename: Kari E J
authors.initials: KE
authors.lastname: Lehtinen
authors.forename: Veli-Matti
authors.initials: VM
authors.lastname: Kerminen