title: The role of sulfuric acid in atmospheric nucleation.
abstract: Nucleation is a fundamental step in atmospheric new-particle formation. However, laboratory experiments on nucleation have systematically failed to demonstrate sulfuric acid particle formation rates as high as those necessary to account for ambient atmospheric concentrations, and the role of sulfuric acid in atmospheric nucleation has remained a mystery. Here, we report measurements of new particles (with diameters of approximately 1.5 nanometers) observed immediately after their formation at atmospherically relevant sulfuric acid concentrations. Furthermore, we show that correlations between measured nucleation rates and sulfuric acid concentrations suggest that freshly formed particles contain one to two sulfuric acid molecules, a number consistent with assumptions that are based on atmospheric observations. Incorporation of these findings into global models should improve the understanding of the impact of secondary particle formation on climate.
authors.affiliation: Leibniz-Institut für Troposphärenforschung e.V., Leipzig 04318, Germany. mikko.sipila@helsinki.fi
authors.forename: Mikko
authors.initials: M
authors.lastname: Sipilä
authors.forename: Torsten
authors.initials: T
authors.lastname: Berndt
authors.forename: Tuukka
authors.initials: T
authors.lastname: Petäjä
authors.forename: David
authors.initials: D
authors.lastname: Brus
authors.forename: Joonas
authors.initials: J
authors.lastname: Vanhanen
authors.forename: Frank
authors.initials: F
authors.lastname: Stratmann
authors.forename: Johanna
authors.initials: J
authors.lastname: Patokoski
authors.forename: Roy L
authors.initials: RL
authors.lastname: Mauldin
authors.forename: Antti-Pekka
authors.initials: AP
authors.lastname: Hyvärinen
authors.forename: Heikki
authors.initials: H
authors.lastname: Lihavainen
authors.forename: Markku
authors.initials: M
authors.lastname: Kulmala