Abstract View
Formation and Properties of Secondary Organic Aerosol Particles Generated by Oxidation of Cyclic and Acyclic Terpenes
ALLA ZELENYUK, Robert VanGundy, David Bell, Pacific Northwest National Laboratory
Abstract Number: 568
Working Group: Aerosol Chemistry
Abstract
Monoterpenes and sesquiterpenes are some of the most common biogenic volatile organic compounds (VOCs) that contribute to formation of significant fraction of atmospheric secondary organic aerosol (SOA). Model treatment of these classes of biogenic VOC emissions and chemistry that leads to SOA formation are typically based on laboratory experiments conducted on a very limited number of SOA precursors (e.g. α-pinene, limonene, β-caryophyllene). Recent studies indicate that plants emit a large variety of both, cyclic and acyclic terpenes, which have different potentials to form SOA. It was shown that SOA formation yields decrease as the fraction of acyclic terpenes in complex VOC mixtures increases, often as a result of environmental stresses from drought, insects, or air pollution. These findings clearly highlight the importance of better understanding oxidation chemistry of acyclic terpenes and the properties of the resulting SOA particles.
We will present the results of a recent study focused on the comparison of formation (yields, size distributions, mass loadings), and properties (composition, density, shape, volatility, viscosity) of SOA particles formed by ozonolysis of cyclic (α-pinene and β-caryophyllene) and acyclic terpenes, including β-ocimene, β-myrcene, and α-farnesene. We find that, consistent with previous studies, SOA yields from ozonolysis of α -farnesene are lower compared to those for β-caryophyllene with the same concentration. Moreover, preliminary data indicate that concentration of VOC strongly effects the viscosity and volatility of SOA particles from both cyclic and acyclic sesquiterpenes. SOA particles formed at lower VOC concentrations are more viscous and less volatile. We show that larger size-selected SOA particles are often aspherical, nearly fractal agglomerates of nanoparticles. However, with time these particles coalesce to form spherical particles, making it possible to estimate particle viscosity as a function of relative humidity.