Composition and volatility of secondary organic aerosol (SOA) formed from oxidation of real tree emissions compared to simplified volatile organic compound (VOC) systems

Abstract

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.

Evolution of volatility and composition in sesquiterpene-mixed and α-pinene secondary organic aerosol particles during isothermal evaporation

“…isoprene-derived SOA) in aerosol-climate models (O'Donnell et al, 2011;Gordon et al, 2016). Or study corroborates previous findings that sesquiterpene-derived particles are more viscous (Saukko et al, 2012), less hygroscopic (Pajunoja et al, 2015) and less volatile (Ylisirnio et al, 2020), compared to αpin SOA particles. These findings are generally corroborated by our study.…”

On the calibration of FIGAERO-ToF-CIMS: importance and impact of calibrant delivery for the particle-phase calibration

“…As both P sat,lit and T max,meas can have significant uncertainties, an appropriate fitting method should be chosen that accounts for errors in both variables, and appropriate fitting uncertainties should be shown with the fitting results. In this study, we used the bivariate least-squares method (York et al, 2004) in Fig. 2b, which was implemented in MATLAB as shown in Pitkänen et al (2016).…”

The importance of sesquiterpene oxidation products for secondary organic aerosol formation in a springtime hemiboreal forest

“…Measurements of inorganic and organic compounds in both gas and particle phases were performed by FIGAERO-CIMS using iodide ionization (HR-ToF-CIMS, Aerodyne Research Inc.). The used FIGAERO unit had been custom built in early 2018 and differs slightly from other designs generally used (Ylisirniö et al, 2020), but the main operation principles are the same as in Lopez-Hilfiker et al (2014). The overall sampling setup used in this study is presented in Fig.…”

“…This result is somewhat unexpected since, generally, the structural diversity of sesquiterpenes exceeds that of monoterpenes due to the many more types of cyclization that are possible with the five additional carbon atoms (Langenheim, 2003). However, the actual structure of the terpenes may also play an important role, since, e.g., cyclic terpenes have been shown to produce more SOA than acyclic ones (e.g., Ylisirniö et al, 2020).…”