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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-982
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
09 Dec 2016
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Dynamic Consideration of Smog Chamber Experiments
Wayne K. Chuang and Neil M. Donahue Carnegie Mellon University Center for Atmospheric Particle Studies, Pittsburgh, USA
Abstract. Recent studies of the α-pinene + ozone reaction focused on particle nucleation show relatively high molar yields of highly oxidized multifunctional organic molecules with very low saturation concentrations that can form and grow new particles on their own. On the other hand, numerous smog-chamber experiments focused on Secondary Organic Aerosol mass yields, interpreted via equilibrium partitioning theory, suggest that the vast majority of SOA from α-pinene is semi volatile. We explore this paradox by employing a dynamical volatility basis set model that reproduces the new-particle growth rates observed in the CLOUD experiment at CERN and then modeling SOA mass yield experiments conducted at CMU. We find that the base-case simulations do over-predict observed SOA mass but by much less than an equilibrium analysis would suggest because delayed condensation of vapors suppresses the apparent mass yields early in the chamber experiments. We further find that a second model featuring substantial oligomerization of semi-volatile monomers can match the CLOUD growth rates with substantially lower SOA mass yields because the lighter monomers have a higher velocity and thus a higher condensation rate for a given mass concentration. However, we also find that if the chemical conditions in CLOUD and the CMU chamber were identical, nucleation would have occurred in the CMU experiments when in fact none occurred. This suggests that the chemical mechanisms differed in the two experiments, perhaps because the high oxidation rates in the SOA formation experiments led to rapid termination of peroxy radical chemistry.

Citation: Chuang, W. K. and Donahue, N. M.: Dynamic Consideration of Smog Chamber Experiments, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-982, in review, 2016.
Wayne K. Chuang and Neil M. Donahue
Wayne K. Chuang and Neil M. Donahue
Wayne K. Chuang and Neil M. Donahue

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Short summary
Experiments on organic aerosol formation is important for our understanding of climate. Recent experiments on the reaction of ozone with alpha-pinene showed high production of extremely low volatility organics. This appeared to contradict prior volatility distributions derived from equilibrium partitioning. We examined this using a dynamic volatility basis set model and found that the delay between the production and condensation of organics is integral to reconciling this difference.
Experiments on organic aerosol formation is important for our understanding of climate. Recent...
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