title: OH reactivity measurements within a boreal forest: evidence for unknown reactive emissions.
abstract: Boreal forests emit large amounts of volatile organic compounds (VOCs) which react with the hydroxyl radical (OH) to influence regional ozone levels and form secondary organic aerosol. Using OH reactivity measurements within a boreal forest in Finland, we investigated the budget of reactive VOCs. OH reactivity was measured using the comparative reactivity method, whereas 30 individual VOCs were measured using proton transfer reaction mass spectrometry, thermal-desorption gas chromatography mass spectrometry, and liquid chromatography mass spectrometry, in August 2008. The measured OH reactivity ranged from below detection limit (3.5 s(-1)), to approximately 60 s(-1) in a single pollution event. The average OH reactivity was approximately 9 s(-1) and no diel variation was observed in the profiles. The measured OH sinks (approximately 30 species) accounted for only 50% of the total measured OH reactivity, implying unknown reactive VOCs within the forest. The five highest measured OH sinks were: monoterpenes (1 s(-1)), CO (0.7 s(-1)), isoprene (0.5 s(-1)), propanal and acetone (0.3 s(-1)), and methane (0.3 s(-1)). We suggest that models be constrained by direct OH reactivity measurements to accurately assess the impact of boreal forest emissions on regional atmospheric chemistry and climate.
authors.affiliation: Max Planck Institute for Chemistry, Department of Air Chemistry, P.O. Box 3060, 55020 Mainz, Germany. v.sinha@mpic.de
authors.forename: Vinayak
authors.initials: V
authors.lastname: Sinha
authors.forename: J
authors.initials: J
authors.lastname: Williams
authors.forename: J
authors.initials: J
authors.lastname: Lelieveld
authors.forename: T M
authors.initials: TM
authors.lastname: Ruuskanen
authors.forename: M K
authors.initials: MK
authors.lastname: Kajos
authors.forename: J
authors.initials: J
authors.lastname: Patokoski
authors.forename: H
authors.initials: H
authors.lastname: Hellen
authors.forename: H
authors.initials: H
authors.lastname: Hakola
authors.forename: D
authors.initials: D
authors.lastname: Mogensen
authors.forename: M
authors.initials: M
authors.lastname: Boy
authors.forename: J
authors.initials: J
authors.lastname: Rinne
authors.forename: M
authors.initials: M
authors.lastname: Kulmala
mesh_terms: D005387:Finland; D017665:Hydroxyl Radical / Q000032:analysis* / Q000737:chemistry*; D008027:Light; D010788:Photosynthesis / Q000528:radiation effects; D013997:Time Factors; D014197:Trees / Q000737:chemistry*; D014919:Wind
chemical_list: D017665:Hydroxyl Radical