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Title: Molecular composition and volatility of isoprene photochemical oxidation secondary organic aerosol under low- and high-NO x conditions

Here, 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 high-resolution 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-HO 2 and low-NO conditions, highly oxygenated (O : C ≥ 1) C 5 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 withmore » 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.« less
Authors:
ORCiD logo [1] ;  [1] ; ORCiD logo [2] ;  [2] ;  [3] ;  [4] ;  [1] ; ORCiD logo [2] ; ORCiD logo [5] ;  [6] ;  [7] ;  [7] ;  [7] ;  [8] ;  [8] ;  [1]
  1. Univ. of Washington, Seattle, WA (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. Univ. of Washington, Seattle, WA (United States); Univ. of Miami, Coral Gables, FL (United States)
  4. Univ. of Washington, Seattle, WA (United States); Paul Scherrer Inst. (PSI), Zurich (Switzerland)
  5. Univ. of Washington, Seattle, WA (United States); Karlsruhe Institute of Technology, Karlsruhe (Germany)
  6. Univ. of Gothenburg, Gothenburg (Sweden)
  7. Univ. of North Carolina, Chapel Hill, NC (United States)
  8. Harvard Univ., Cambridge, MA (United States)
Publication Date:
Report Number(s):
PNNL-SA-119934
Journal ID: ISSN 1680-7324; KP1701000
Grant/Contract Number:
AC05-76RL01830; SC0011791
Type:
Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 17; Journal Issue: 1; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; isoprene; photochemical oxidation; secondary organic aerosol
OSTI Identifier:
1338140
Alternate Identifier(s):
OSTI ID: 1339791; OSTI ID: 1390603