title: Solar eclipse demonstrating the importance of photochemistry in new particle formation.
abstract: Solar eclipses provide unique possibilities to investigate atmospheric processes, such as new particle formation (NPF), important to the global aerosol load and radiative balance. The temporary absence of solar radiation gives particular insight into different oxidation and clustering processes leading to NPF. This is crucial because our mechanistic understanding on how NPF is related to photochemistry is still rather limited. During a partial solar eclipse over Finland in 2015, we found that this phenomenon had prominent effects on atmospheric on-going NPF. During the eclipse, the sources of aerosol precursor gases, such as sulphuric acid and nitrogen- containing highly oxidised organic compounds, decreased considerably, which was followed by a reduced formation of small clusters and nanoparticles and thus termination of NPF. After the eclipse, aerosol precursor molecule concentrations recovered and re-initiated NPF. Our results provide direct evidence on the key role of the photochemical production of sulphuric acid and highly oxidized organic compounds in maintaining atmospheric NPF. Our results also explain the rare occurrence of this phenomenon under dark conditions, as well as its seemingly weak connection with atmospheric ions.
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Tuija
authors.initials: T
authors.lastname: Jokinen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Jenni
authors.initials: J
authors.lastname: Kontkanen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.|Paul Scherrer Institute, 5232 Villigen - PSI, Switzerland.
authors.forename: Katrianne
authors.initials: K
authors.lastname: Lehtipalo
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Hanna E
authors.initials: HE
authors.lastname: Manninen
authors.affiliation: Department of Forest Sciences, P.O. Box 27, FIN-00014 University of Helsinki, Finland.|Hyytiälä Forestry Field Station, Hyytiäläntie 124, FIN-35500 Korkeakoski, Finland.
authors.forename: Juho
authors.initials: J
authors.lastname: Aalto
authors.affiliation: Department of Forest Sciences, P.O. Box 27, FIN-00014 University of Helsinki, Finland.
authors.forename: Albert
authors.initials: A
authors.lastname: Porcar-Castell
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Olga
authors.initials: O
authors.lastname: Garmash
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Tuomo
authors.initials: T
authors.lastname: Nieminen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Mikael
authors.initials: M
authors.lastname: Ehn
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Kangasluoma
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Junninen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.|Department of Forest Sciences, P.O. Box 27, FIN-00014 University of Helsinki, Finland.|Hyytiälä Forestry Field Station, Hyytiäläntie 124, FIN-35500 Korkeakoski, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Levula
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Duplissy
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Lauri R
authors.initials: LR
authors.lastname: Ahonen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Pekka
authors.initials: P
authors.lastname: Rantala
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Liine
authors.initials: L
authors.lastname: Heikkinen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Chao
authors.initials: C
authors.lastname: Yan
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Sipilä
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.|Aerodyne Research Inc., Billerica, Massachusetts 01821, USA.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Worsnop
authors.affiliation: Department of Forest Sciences, P.O. Box 27, FIN-00014 University of Helsinki, Finland.
authors.forename: Jaana
authors.initials: J
authors.lastname: Bäck
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Tuukka
authors.initials: T
authors.lastname: Petäjä
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Veli-Matti
authors.initials: VM
authors.lastname: Kerminen
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Kulmala