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| Titel |
Investigation of particle and vapor wall-loss effects on controlled wood-smoke smog-chamber experiments |
| VerfasserIn |
Q. Bian, A. A. May, S. M. Kreidenweis, J. R. Pierce |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 19 ; Nr. 15, no. 19 (2015-10-06), S.11027-11045 |
| Datensatznummer |
250120075
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| Publikation (Nr.) |
 copernicus.org/acp-15-11027-2015.pdf |
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| Zusammenfassung |
Smog chambers are extensively used to study processes that drive gas and
particle evolution in the atmosphere. A limitation of these experiments is
that particles and gas-phase species may be lost to chamber walls on shorter
timescales than the timescales of the atmospheric processes being studied in
the chamber experiments. These particle and vapor wall losses have been
investigated in recent studies of secondary organic aerosol (SOA) formation,
but they have not been systematically investigated in experiments of primary
emissions from combustion. The semi-volatile nature of combustion emissions
(e.g. from wood smoke) may complicate the behavior of particle and vapor
wall deposition in the chamber over the course of the experiments due to the
competition between gas/particle and gas/wall partitioning. Losses of vapors
to the walls may impact particle evaporation in these experiments, and
potential precursors for SOA formation from combustion may be lost to the
walls, causing underestimations of aerosol yields. Here, we conduct
simulations to determine how particle and gas-phase wall losses contributed
to the observed evolution of the aerosol during experiments in the third
Fire Lab At Missoula Experiment (FLAME III). We use the TwO-Moment Aerosol
Sectional (TOMAS) microphysics algorithm coupled with the organic volatility
basis set (VBS) and wall-loss formulations to examine the predicted extent
of particle and vapor wall losses. We limit the scope of our study to the
dark periods in the chamber before photo-oxidation to simplify the aerosol
system for this initial study.
Our model simulations suggest that over one-third of the initial
particle-phase organic mass (41 %) was lost during the experiments, and
over half of this particle-organic mass loss was from direct particle wall
loss (65 % of the loss) with the remainder from evaporation of the
particles driven by vapor losses to the walls (35 % of the loss). We
perform a series of sensitivity tests to understand uncertainties in our
simulations. Uncertainty in the initial wood-smoke volatility distribution
contributes 18 % uncertainty to the final particle-organic mass remaining
in the chamber (relative to base-assumption simulation). We show that the
total mass loss may depend on the effective saturation concentration of vapor
with respect to the walls as these values currently vary widely in the
literature. The details of smoke dilution during the filling of smog chambers
may influence the mass loss to the walls, and a dilution of ~ 25:1
during the experiments increased particle-organic mass loss by 33 %
compared to a simulation where we assume the particles and vapors are
initially in equilibrium in the chamber. Finally, we discuss how our findings
may influence interpretations of emission factors and SOA production in
wood-smoke smog-chamber experiments. |
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