10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Recent Advances in Understanding on the Relation between Ion Composition and Ion-induced Nucleation in the Boreal Forest in Southern Finland
CHAO YAN, Clemence Rose, Lubna Dada, Federico Bianchi, Siegfried Schobesberger, Heikki Junninen, Katrianne Lehtipalo, Wei Nie, Tuija Jokinen, Nina Sarnela, Yonghong Wang, Qiaozhi Zha, Olga Garmash, Mikko Sipilä, Tuukka Petäjä, Veli-Matti Kerminen, Mikael Ehn, Markku Kulmala, University of Helsinki, Finland
Abstract Number: 689 Working Group: Aerosol Chemistry
Abstract New particle formation (NPF) potentially contributes to a significant fraction of the atmospheric aerosol particles, hence affect the air quality and climate. One critical step of NPF is to form stable clusters for sebsequent condensational growth. Recent chamber studies have demonstrated the significant enhancement of NPF by atmospheric ions stabilizing the initial clusters (the so-called ion-induced nucleation, e.g., Kirkby et al., 2011, Kirkby et al., 2016). However, it has remained unclear if these chamber findings are directly applicable to the more complicated atmosphere, mostly due to the incomplete understanding of the formation of atmospheric ion clusters as well as difficulties in characterizing their subsequent growth.
The ion composition has been first measured by Ehn et al., (2010) at the boreal forest in southern Finland (Hyytiälä station) using an atmospheric-pressure-interface time-of-flight mass spectrometer (APi-TOF). The results revealed clear diurnal variation of the ion composition: Sulfuric acid ion clusters are dominant during the daytime, whereas adducts of highly oxygenated organic compounds (HOM) and nitrate (HOMNO3-) are more prominent during the night. This observation has recently been deepened by Bianchi et al., (2017), who have categorized ion cluster composition into finer groups: Clusters of nitrate- or non-nitrate HOMs with HSO4- or NO3- adducts were explicitly separated. However, it has not been dedicatedly studied how ion composition affects IIN.
We characterized the anion composition and IIN at the Hyytiälä station using longer data sets from 3 consecutive springs (2011-2013, 167 measurement days in total), with a special focus on the relation between ion composition and IIN. Our results show that IIN at Hyytiälä station is driven by different mechanisms, which vary diurnally and seasonally. More specifically, H2SO4-NH3 and HOM clusters drive daytime IIN alternately, which is regulated by temperature, whereas all nighttime IIN events are driven by HOM clusters. The observational details of the formation and growth of ion clusters will be presented.