Measurement of Oxygen-to-Carbon Ratios of Organic Aerosols and Implications for the Atmospheric Evolution of SOA

HR: 09:30h
AN: A51H-06 [Abstracts]
TI: Measurement of Oxygen-to-Carbon Ratios of Organic Aerosols and Implications for the Atmospheric Evolution of SOA
AU: * Jimenez, J L
EM: jose.jimenez@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Aiken, A C
EM: allison.Aiken@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: DeCarlo, P F
EM: peter.decarlo@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Ulbrich, I M
EM: ingrid.ulbrich@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Huffman, J A
EM: alex.huffman@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Docherty, K
EM: kenneth.docherty@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Kimmel, J R
EM: joel.kimmel@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Mohr, C
EM: claudia.mohr@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Kroll, J
EM: kroll@aerodyne.com
AF: Aerodyne Research, 45 Manning Rd., Billerica, MA 01821, United States
AU: Worsnop, D R
EM: worsnop@aerodyne.com
AF: Aerodyne Research, 45 Manning Rd., Billerica, MA 01821, United States
AU: Canagaratna, M R
EM: mrcana@aerodyne.com
AF: Aerodyne Research, 45 Manning Rd., Billerica, MA 01821, United States
AU: Onasch, T
EM: onasch@aerodyne.com
AF: Aerodyne Research, 45 Manning Rd., Billerica, MA 01821, United States
AU: Zhang, Q
EM: dkwzhang@gmail.com
AF: SUNY-Albany, Atmospheric Sciences Research Center, Albany, NY 12203, United States
AU: Sun, Y
EM: sunyele@gmail.com
AF: SUNY-Albany, Atmospheric Sciences Research Center, Albany, NY 12203, United States
AU: Ziemann, P J
EM: pziemann@ucr.edu
AF: University of California-Riverside, Air Pollution Research Center, Riverside, CA 92521, United States
AU: Alfarra, M R
EM: rami.alfarra@psi.ch
AF: Paul Scherrer Institut, Laboratory for Atmospheric Chemistry, Villigen, CH1210, Switzerland
AU: Balstensperger, U
EM: urs.balstensperger@psi.ch
AF: Paul Scherrer Institut, Laboratory for Atmospheric Chemistry, Villigen, CH1210, Switzerland
AU: Prevot, A
EM: andre.prevot@psi.ch
AF: Paul Scherrer Institut, Laboratory for Atmospheric Chemistry, Villigen, CH1210, Switzerland
AU: Dommen, J
EM: josef.dommen@psi.ch
AF: Paul Scherrer Institut, Laboratory for Atmospheric Chemistry, Villigen, CH1210, Switzerland
AB: We present a new elemental analysis (EA) technique for organic aerosols (OA) that allows fast on-line analysis (10 s) and reduces the required sample size to ~ 1 ng, about 6 orders of magnitude less than standard techniques. The composition of the analyzed samples is approximated by the average elemental composition of the ions from high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) spectra, with a calibration to correct for biases introduced by the fragmentation process. EA of organic species can be performed on organic/inorganic mixtures. Elemental ratios for the total organic mass, such as oxygen/carbon (O/C), hydrogen/carbon (H/C), and nitrogen/carbon (N/C), in addition to the organic mass to organic carbon ratio (OM/OC), can be determined. Additionally, we provide approximations that can be used with unit mass resolution (UMR) AMS datasets collected with the quadrupole (Q-AMS) and C-ToF-AMS. We apply this method to urban and regional organic aerosols measured from ground sites and aircraft during MILAGRO and SOAR-1, to chamber secondary OA (SOA), and to source measurements of several primary OA sources. A clear diurnal cycle is observed in urban areas for O/C with a maximum in the afternoon due to SOA formation and a minimum during the morning rush hour due to primary OA (POA) emissions. The average O/C atomic ratio of the total urban OA varies between about 0.2 and 0.7. H/C has the opposite diurnal cycle due to higher H content in POA than SOA. N/C is low around 0.05 and relatively constant, with some upward excursions in the early morning due to amine-containing plumes. EA can also be applied to OA components extracted with Positive Matrix Factorization (PMF). Hydrocarbon-like OA (HOA, a POA surrogate) has low O/C ratios ~ 0.1, while fresh oxygenated OA Type II (OOA-II, a surrogate for fresh SOA) has O/C ~ 0.6, and regional aged OOA (OOA-I) reaches O/C ~ 1. Chamber SOA has a similar O/C (and mass spectra) as ambient fresh SOA. We clearly observe the evolution of OOA-II into OOA-I during photochemistry in several case studies. Time series and thermal denuder data also indicate that OOA-I is less volatile than OOA-II, consistent with the higher O/C of the former, and potentially with oligomer formation during aging. Our results indicate that fresh urban SOA is similar to chamber SOA, but that a key parameter missing from chamber studies is increased and realistic aging. Finally, the identification of OOA-II and OOA-I with similar properties in multiple environments highlight the global importance of these results.
UR: http://cires.colorado.edu/jimenez/ams.html
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting