TY - JOUR
T1 - Molecular composition and volatility of isoprene photochemical oxidation secondary organic aerosol under low- and high-NOx conditions
AU - D'Ambro, Emma L.
AU - Lee, Ben H.
AU - Liu, Jiumeng
AU - Shilling, John E.
AU - Gaston, Cassandra J.
AU - Lopez-Hilfiker, Felipe D.
AU - Schobesberger, Siegfried
AU - Zaveri, Rahul A.
AU - Mohr, Claudia
AU - Lutz, Anna
AU - Zhang, Zhenfa
AU - Gold, Avram
AU - Surratt, Jason D.
AU - Rivera-Rios, Jean C.
AU - Keutsch, Frank N.
AU - Thornton, Joel A.
N1 - Funding Information:
This work was supported by the US Department of Energy ASR grants DE-SC0011791. Emma L. D'Ambro was supported by the National Science Foundation Graduate Research Fellowship under grant no. DGE-1256082. Ben H. Lee was supported by the National Oceanic and Atmospheric Administration (NOAA) Climate and Global Change Postdoctoral Fellowship Program. Frank N. Keutsch and Jean C. Rivera-Rios were supported by the National Science Foundation (AGS 1628491 and 1628530). PNNL authors were supported by the US Department of Energy, Office of Biological and Environmental Research as part of the ASR program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830. We thank J. D. Crounse for useful discussions.
PY - 2017/1/4
Y1 - 2017/1/4
N2 - We present measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation in an environmental simulation chamber at a variety of oxidant conditions and using dry neutral seed particles to suppress acid-catalyzed multiphase chemistry. A highresolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) utilizing iodide-adduct ionization coupled to the Filter Inlet for Gases and Aerosols (FIGAERO) allowed for simultaneous online sampling of the gas and particle composition. Under high-HO2 and low-NO conditions, highly oxygenated (O:C ≥ 1) C5 compounds were major components (50%) of SOA. The SOA composition and effective volatility evolved both as a function of time and as a function of input NO concentrations. Organic nitrates increased in both the gas and particle phases as input NO increased, but the dominant non-nitrate particle-phase components monotonically decreased. We use comparisons of measured and predicted gas-particle partitioning of individual components to assess the validity of literature-based group-contribution methods for estimating saturation vapor concentrations. While there is evidence for equilibrium partitioning being achieved on the chamber residence timescale (5.2 h) for some individual components, significant errors in group-contribution methods are revealed. In addition, > 30 % of the SOA mass, detected as low-molecular-weight semivolatile compounds, cannot be reconciled with equilibrium partitioning. These compounds desorb from the FIGAERO at unexpectedly high temperatures given their molecular composition, which is indicative of thermal decomposition of effectively lower-volatility components such as larger molecular weight oligomers.
AB - We present measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation in an environmental simulation chamber at a variety of oxidant conditions and using dry neutral seed particles to suppress acid-catalyzed multiphase chemistry. A highresolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) utilizing iodide-adduct ionization coupled to the Filter Inlet for Gases and Aerosols (FIGAERO) allowed for simultaneous online sampling of the gas and particle composition. Under high-HO2 and low-NO conditions, highly oxygenated (O:C ≥ 1) C5 compounds were major components (50%) of SOA. The SOA composition and effective volatility evolved both as a function of time and as a function of input NO concentrations. Organic nitrates increased in both the gas and particle phases as input NO increased, but the dominant non-nitrate particle-phase components monotonically decreased. We use comparisons of measured and predicted gas-particle partitioning of individual components to assess the validity of literature-based group-contribution methods for estimating saturation vapor concentrations. While there is evidence for equilibrium partitioning being achieved on the chamber residence timescale (5.2 h) for some individual components, significant errors in group-contribution methods are revealed. In addition, > 30 % of the SOA mass, detected as low-molecular-weight semivolatile compounds, cannot be reconciled with equilibrium partitioning. These compounds desorb from the FIGAERO at unexpectedly high temperatures given their molecular composition, which is indicative of thermal decomposition of effectively lower-volatility components such as larger molecular weight oligomers.
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U2 - 10.5194/acp-17-159-2017
DO - 10.5194/acp-17-159-2017
M3 - Article
AN - SCOPUS:85008950470
VL - 17
SP - 159
EP - 174
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
SN - 1680-7316
IS - 1
ER -