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  1. Article ; Online: Modeling the multiday evolution and aging of secondary organic aerosol during MILAGRO 2006.

    Dzepina, Katja / Cappa, Christopher D / Volkamer, Rainer M / Madronich, Sasha / Decarlo, Peter F / Zaveri, Rahul A / Jimenez, Jose L

    Environmental science & technology

    2011  Volume 45, Issue 8, Page(s) 3496–3503

    Abstract: In this study, we apply several recently proposed models to the evolution of secondary organic aerosols (SOA) and organic gases advected from downtown Mexico City at an altitude of ∼3.5 km during three days of aging, in a way that is directly comparable ... ...

    Abstract In this study, we apply several recently proposed models to the evolution of secondary organic aerosols (SOA) and organic gases advected from downtown Mexico City at an altitude of ∼3.5 km during three days of aging, in a way that is directly comparable to simulations in regional and global models. We constrain the model with and compare its results to available observations. The model SOA formed from oxidation of volatile organic compounds (V-SOA) when using a non-aging SOA parameterization cannot explain the observed SOA concentrations in aged pollution, despite the increasing importance of the low-NO(x) channel. However, when using an aging SOA parameterization, V-SOA alone is similar to the regional aircraft observations, highlighting the wide diversity in current V-SOA formulations. When the SOA formed from oxidation of semivolatile and intermediate volatility organic vapors (SI-SOA) is computed following Robinson et al. (2007) the model matches the observed SOA mass, but its O/C is ∼2× too low. With the parameterization of Grieshop et al. (2009), the total SOA mass is ∼2× too high, but O/C and volatility are closer to the observations. Heating or dilution cause the evaporation of a substantial fraction of the model SOA; this fraction is reduced by aging although differently for heating vs dilution. Lifting of the airmass to the free-troposphere during dry convection substantially increases SOA by condensation of semivolatile vapors; this effect is reduced by aging.
    MeSH term(s) Aerosols/analysis ; Aerosols/chemistry ; Air Pollutants/analysis ; Air Pollutants/chemistry ; Environmental Monitoring/methods ; Models, Chemical ; Organic Chemicals/analysis ; Organic Chemicals/chemistry ; Phase Transition ; Time ; Volatilization
    Chemical Substances Aerosols ; Air Pollutants ; Organic Chemicals
    Language English
    Publishing date 2011-04-15
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ISSN 1520-5851
    ISSN (online) 1520-5851
    DOI 10.1021/es103186f
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article: O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry.

    Aiken, Allison C / Decarlo, Peter F / Kroll, Jesse H / Worsnop, Douglas R / Huffman, J Alex / Docherty, Kenneth S / Ulbrich, Ingrid M / Mohr, Claudia / Kimmel, Joel R / Sueper, Donna / Sun, Yele / Zhang, Qi / Trimborn, Achim / Northway, Megan / Ziemann, Paul J / Canagaratna, Manjula R / Onasch, Timothy B / Alfarra, M Rami / Prevot, Andre S H /
    Dommen, Josef / Duplissy, Jonathan / Metzger, Axel / Baltensperger, Urs / Jimenez, Jose L

    Environmental science & technology

    2008  Volume 42, Issue 12, Page(s) 4478–4485

    Abstract: A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon ...

    Abstract A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches approximately 0.9. The hydrogen-to-carbon (H/C, 1.4--1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, approximately 0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R2 = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/OC trends. The highest O/C and OM/OC (1.0 and 2.5, respectively) are observed for aged ambient oxygenated OA, significantly exceeding values for traditional chamber SOA,while laboratory-produced primary biomass burning OA (BBOA) is similar to ambient BBOA, O/C of 0.3--0.4. Hydrocarbon-like OA (HOA), a surrogate for urban combustion POA, has the lowest O/C (0.06--0.10), similar to vehicle exhaust. An approximation for predicting O/C from unit mass resolution data is also presented.
    MeSH term(s) Aerosols/analysis ; Calibration ; Mass Spectrometry/methods
    Chemical Substances Aerosols
    Language English
    Publishing date 2008-03-05
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ISSN 0013-936X
    ISSN 0013-936X
    DOI 10.1021/es703009q
    Database MEDical Literature Analysis and Retrieval System OnLINE

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