Composition and volatility of secondary organic aerosol (SOA) formed from oxidation of real tree emissions compared to simplified volatile organic compound (VOC) systems
2020
Abstract. Secondary organic aerosol (SOA) is an important constituent of the
atmosphere where SOA particles are formed chiefly by the condensation or
reactive uptake of oxidation products of volatile organic compounds (VOCs).
The mass yield in SOA particle formation, as well as the chemical
composition and volatility of the particles, is determined by the identity
of the VOC precursor(s) and the oxidation conditions they experience. In
this study, we used an oxidation flow reactor to generate biogenic SOA from
the oxidation of Scots pine emissions. Mass yields, chemical composition
and volatility of the SOA particles were characterized and compared with SOA
particles formed from oxidation of α -pinene and from a mixture of
acyclic–monocyclic sesquiterpenes (farnesenes and bisabolenes), which are
significant components of the Scots pine emissions. SOA mass yields for
Scots pine emissions dominated by farnesenes were lower than for α -pinene but higher than for the artificial mixture of farnesenes and
bisabolenes. The reduction in the SOA yield in the farnesene- and
bisabolene-dominated mixtures is due to exocyclic C = C bond scission in
these acyclic–monocyclic sesquiterpenes during ozonolysis leading to smaller
and generally more volatile products. SOA particles from the oxidation of
Scots pine emissions had similar or lower volatility than SOA particles
formed from either a single precursor or a simple mixture of VOCs. Applying
physical stress to the Scots pine plants increased their monoterpene, especially monocyclic β -phellandrene, emissions, which further decreased SOA particle volatility and increased SOA mass yield. Our results
highlight the need to account for the chemical complexity and structure of
real-world biogenic VOC emissions and stress-induced changes to plant
emissions when modelling SOA production and properties in the atmosphere.
These results emphasize that a simple increase or decrease in relative
monoterpene and sesquiterpene emissions should not be used as an indicator of
SOA particle volatility.
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