title: Parameterization of thermal properties of aging secondary organic aerosol produced by photo-oxidation of selected terpene mixtures.
abstract: Formation and evolution of secondary organic aerosols (SOA) from biogenic VOCs influences the Earth's radiative balance. We have examined the photo-oxidation and aging of boreal terpene mixtures in the SAPHIR simulation chamber. Changes in thermal properties and chemical composition, deduced from mass spectrometric measurements, were providing information on the aging of biogenic SOA produced under ambient solar conditions. Effects of precursor mixture, concentration, and photochemical oxidation levels (OH exposure) were evaluated. OH exposure was found to be the major driver in the long term photochemical transformations, i.e., reaction times of several hours up to days, of SOA and its thermal properties, whereas the initial concentrations and terpenoid mixtures had only minor influence. The volatility distributions were parametrized using a sigmoidal function to determine TVFR0.5 (the temperature yielding a 50% particle volume fraction remaining) and the steepness of the volatility distribution. TVFR0.5 increased by 0.3±0.1% (ca. 1 K), while the steepness increased by 0.9±0.3% per hour of 1×10(6) cm(-3) OH exposure. Thus, aging reduces volatility and increases homogeneity of the vapor pressure distribution, presumably because highly volatile fractions become increasingly susceptible to gas phase oxidation, while less volatile fractions are less reactive with gas phase OH.
authors.affiliation: Atmospheric Science, Department of Chemistry and Molecular Biology, University of Gothenburg , Gothenburg S-405 30, Sweden.
authors.forename: Eva U
authors.initials: EU
authors.lastname: Emanuelsson
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Mentel
authors.forename: Agot K
authors.initials: AK
authors.lastname: Watne
authors.forename: Christian
authors.initials: C
authors.lastname: Spindler
authors.forename: Birger
authors.initials: B
authors.lastname: Bohn
authors.forename: Theo
authors.initials: T
authors.lastname: Brauers
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Dorn
authors.forename: Asa M
authors.initials: AM
authors.lastname: Hallquist
authors.forename: Rolf
authors.initials: R
authors.lastname: Häseler
authors.forename: Astrid
authors.initials: A
authors.lastname: Kiendler-Scharr
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Müller
authors.forename: Håkan
authors.initials: H
authors.lastname: Pleijel
authors.forename: Franz
authors.initials: F
authors.lastname: Rohrer
authors.forename: Florian
authors.initials: F
authors.lastname: Rubach
authors.forename: Eric
authors.initials: E
authors.lastname: Schlosser
authors.forename: Ralf
authors.initials: R
authors.lastname: Tillmann
authors.forename: Mattias
authors.initials: M
authors.lastname: Hallquist
mesh_terms: D000336:Aerosols / Q000032:analysis / Q000737:chemistry; D000393:Air Pollutants / Q000032:analysis / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D013729:Terpenes / Q000032:analysis / Q000737:chemistry*; D014835:Volatilization
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D005740:Gases; D013729:Terpenes