AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Molecular Composition of Water-Soluble Organic Carbon in Nonurban Aerosols
LYNN MAZZOLENI, Parichehr Saranjampour, Megan Dalbec, Vera Samburova, Anna Gannet Hallar, Barbara Zielinska, Douglas Lowenthal, Michigan Technological University
Abstract Number: 402 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Water-soluble organic carbon (WSOC) is a complex mixture of thousands of organic compounds which may have significant influence on the climate-relevant properties of atmospheric aerosols. An improved understanding of the molecular composition of WSOC is needed to evaluate the effect of aerosol composition upon aerosol physical properties. Products of gas phase, aqueous phase and particle phase reactions contribute to pre-existing aerosol organic mass or nucleate new aerosol particles. Thus, ambient aerosols carry a complex array of WSOC components with variable chemical signatures depending upon its origin and aerosol life-cycle processes. In this work, ultrahigh-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize aerosol WSOC collected during the summer of 2010 at the Storm Peak Laboratory (3210 m asl) near Steamboat Springs, CO. Approximately 4000 molecular formulas were assigned in the mass range of 100–800 Da after negative-ion electrospray ionization. More than 50% of the assigned formulas contained nitrogen and/or sulfur. The double bond equivalents (DBE) of the molecular formulas were inversely proportional to the O:C ratio, despite a relatively constant H:C ratio of ~1.5. The observed trends indicate significant non-oxidative accretion reaction pathways for the formation of high molecular weight WSOC components. Several of the most prominent WSOC molecular formulas matched the most prominent β-caryophyllene/ozonolysis SOA molecular formulas, including C$_(14)H$_(22)O$_7 (relative abundance (RA) = 95%), C$_(14)H$_(22)O$_6 (RA = 84%) and C$_(15)H$_(24)O$_7 (RA = 78%). Another compound, C$_(10)H$_(17)NO$_(10)S interpreted to be a nitrated analog of secondary organosulfates found in chamber studies of β-pinene oxidation, was assigned with very high RA. Based on molecular trends and a large number of common formulas, an overall SOA-like character was deduced, however a majority of the nitrogen and/or sulfur containing molecular formulas cannot be matched to experimental SOA. Their origin and transformation processes are yet highly uncertain.