title: Experimental observation of strongly bound dimers of sulfuric acid: application to nucleation in the atmosphere.
abstract: Sulfuric acid is a key compound in atmospheric nucleation. Here we report on the observation of a close-to-collision-limited sulfuric acid dimer formation in atmospherically relevant laboratory conditions in the absence of measurable quantities of ammonia or organics. The observed dimer formation rate was clearly higher than the measured new particle formation rate at ∼1.5  nm suggesting that the rate limiting step for the nucleation takes place after the dimerization step. The quantum chemical calculations suggested that even in the ultraclean conditions there exist (a) stabilizing compound(s) with (a) concentration(s) high enough to prevent the dimer evaporation. Such a stabilizing compound should be abundant enough in any natural environment and would therefore not limit the formation of sulfuric acid dimers in the atmosphere.
authors.affiliation: Department of Physics, University of Helsinki, Helsinki, Finland. tuukka.petaja@helsinki.fi
authors.forename: Tuukka
authors.initials: T
authors.lastname: Petäjä
authors.forename: Mikko
authors.initials: M
authors.lastname: Sipilä
authors.forename: Pauli
authors.initials: P
authors.lastname: Paasonen
authors.forename: Tuomo
authors.initials: T
authors.lastname: Nieminen
authors.forename: Theo
authors.initials: T
authors.lastname: Kurtén
authors.forename: Ismael K
authors.initials: IK
authors.lastname: Ortega
authors.forename: Frank
authors.initials: F
authors.lastname: Stratmann
authors.forename: Hanna
authors.initials: H
authors.lastname: Vehkamäki
authors.forename: Torsten
authors.initials: T
authors.lastname: Berndt
authors.forename: Markku
authors.initials: M
authors.lastname: Kulmala