| Presentations and Publications
Donahue, N.M., Huff Hartz, K.E., Chuong, B., Presto, A., Stanier, C., Rosenhørn, T., Robinson, A.L., and Pandis, S.N., “Critical factors determining the variation in SOA yields from terpene ozonolysis: A combined experimental and computational study”, Faraday Discussions, Vol. 130, 2005, pp. 1-15.
A substantial fraction of the total ultrafine particulate mass is comprised of organic
compounds. Of this fraction, a significant subfraction is secondary organic aerosol (SOA),
meaning that the compounds are a by-product of chemistry in the atmosphere. However,
our understanding of the kinetics and mechanisms leading to and following SOA
formation is in its infancy. We lack a clear description of critical phenomena; we often
don’t know the key, rate limiting steps in SOA formation mechanisms. We know almost
nothing about aerosol yields past the first generation of oxidation products. Most
importantly, we know very little about the derivatives in these mechanisms; we do not
understand how changing conditions, be they precursor levels, oxidant concentrations, coreagent
concentrations (i.e., the VOC/NOx ratio) or temperature will influence the yields of
SOA. In this paper we explore the connections between fundamental details of physical
chemistry and the multitude of steps associated with SOA formation, including the initial
gas-phase reaction mechanisms leading to condensible products, the phase partitioning
itself, and the continued oxidation of the condensed-phase organic products. We show that
SOA yields in the a-pinene þ ozone are highly sensitive to NOx, and that SOA yields from
b-caryophylene þ ozone appear to increase with continued ozone exposure, even as
aerosol hygroscopicity increases as well. We suggest that SOA yields are likely to increase
substantially through several generations of oxidative processing of the semi-volatile
products.
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