Biogenic Sesquiterpenes and Atmospheric New Particle Formation: A Boreal Forest Site Investigation.

The link between ambient biogenic volatile organic compounds (VOCs) and secondary new particle formation has been hypothesized for a long time. However no clear indication for the participation in the very first steps has been found yet. In this study we link atmospheric air ion concentrations between 0.56 and 0.75 nm in mobility-derived diameter to a first stage oxidation product of sesquiterpenes, the C15-stabilized Criegee intermediates. These intermediates, which are obtained from air ion measurements at Hyytiälä (Finland), react subsequently with either sulphuric acid to form organo sulfates or with pinonaldehyde producing secondary ozonides to initiate new particle formation. Assuming activation to occur by reactive sulphuric acid uptake, we calculated new particle formation rates observed during the BACCI/QUEST IV campaign and found a good match between the calculated and the measured ones. However, the height of new particle formation is dependent on the stability of the boundary layer and the resulting vertical profile of sesquiterpenes. The nice agreement between measurements and calculations provide a first indication about the importance of the biosphere with respect to nucleation and a further feedback within the climate system. Keywords Heterogeneous nucleation, sesquiterpenes, sulphuric acid, boreal forest [ABSTRACT FROM AUTHOR]