Accounting for the chemical complexity of VOCs

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A new study led by the University of Eastern Finland has found that the secondary organic aerosol (SOA) mass yields for Scots pine emissions, dominated by farnesenes (six closely related chemical compounds which are all sesquiterpenes), were observed to be lower than emissions generated from alpha-pinene (an organic compound of the terpene class) but higher than those produced by mixture of farnesenes and bisabolenes (a group of closely related natural chemical compounds which are classified as sesquiterpenes).

The composition of plant-emitted VOCs and their potential to form SOA was studied by the report’s authors using a 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 artificially formed from oxidation of α-pinene and a mixture of acyclic–monocyclic sesquiterpenes (farnesenes and bisabolenes), which are significant components of the Scots pine emissions.

According to the study, the reduction in the SOA yield for the farnesene- and bisabolene-dominated mixtures is related to their chemical structure, since ozonolysis causes a scission of exocyclic C=C bonds in these acyclic–monocyclic sesquiterpenes, leading to smaller and generally more volatile oxidation products. The study revealed the importance to account for the chemical complexity of VOCs and resulting oxidation products when evaluating SOA yields.

The findings are significant because secondary organic aerosols (SOA) are important constituents of the atmosphere and are known to influence climate and air quality. SOA are formed in complex atmospheric reactions between volatile organic compounds (VOCs) and oxidants (e.g. OH, O<span style=”font-size: 50%; vertical-align: sub;”>3 </span> and NOx).

The mass yield of SOA, as well as the chemical composition and volatility of the particles, is determined by the type of VOC precursor(s), the atmospheric oxidative conditions and the type of oxidation products formed.

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