Large Discrepancy in the Formation of Secondary Organic Aerosols from Structurally Similar Monoterpenes

Abstract

The two monoterpenes, Δ3-carene and α-pinene, have very similar chemical structures, which leads to the assumption that the formation of secondary organic aerosol (SOA) is also similar. This study aims to investigate if the formation of SOA from ozonolysis of Δ3-carene and α-pinene is actually analogous. This is addressed by conducting smog chamber studies of Δ3-carene ozonolysis and comparing the results to similar studies of α-pinene. Detailed offline analysis using ultra-high-performance liquid chromatography coupled to mass spectrometry seeks to elucidate differences in the product distribution between Δ3-carene and α-pinene. The experimental findings are supported by quantum chemical calculations of formation free energies of the first-generation oxidation products, cis-3-caric acid and cis-pinic acid. The smog chamber studies and detailed offline analysis show a considerable difference in the SOA formation from Δ3-carene and α-pinene. Δ3-carene produces higher SOA mass and larger particles, whereas α-pinene produces a larger number of smaller particles. This indicates that Δ3-carene oxidation products tend to condense on already existing particles, whereas α-pinene oxidation products to a larger degree contribute to new particle formation. The detailed offline analysis shows a much less diverse product distribution in Δ3-carene SOA compared to α-pinene SOA. In addition, three dimers from Δ3-carene are identified for the first time. The quantum chemical calculations indicate that cis-3-caric acid is expected to be more efficient in condensing on already existing particles compared to cis-pinic acid, which is in good agreement with the experimental results.

Comparison of saturation vapor pressures of <i>α</i>-pinene + O<sub>3</sub> oxidation products derived from COSMO-RS computations and thermal desorption experiments

“…Hyttinen et al: Vapor pressures of α-pinene + O 3 products Monoterpenes (C 10 H 16 ) are an abundant class of BVOCs emitted by various plants (Guenther et al, 1995). The oxidation mechanisms of monoterpene reactants vary significantly, leading to products with different SOA formation capabilities (Thomsen et al, 2021). Additionally, the initial oxidant (i.e., OH, O 3 and NO 3 ) affects the SOA formation rates of the oxidation products (Kurtén et al, 2017).…”

“…For example, αpinene, a very abundant monoterpene in the atmosphere, has been widely studied in both laboratory and field experiments (Docherty et al, 2005;Hall and Johnston, 2011;Hao et al, 2011;Ehn et al, 2012Ehn et al, , 2014Kristensen et al, 2014;Lopez-Hilfiker et al, 2015;McVay et al, 2016;D'Ambro et al, 2018;Huang et al, 2018;Claflin et al, 2018;Ye et al, 2019), and α-pinene oxidation, with both O 3 and OH, is efficient at producing oxygenated organic molecules and SOA. Consequently, the oxidation mechanism and potential structures of α-pinene + O 3 products have been extensively studied both experimentally and computationally Berndt et al, 2018;Kurtén et al, 2015;Iyer et al, 2021;Lignell et al, 2013;Aljawhary et al, 2016;Mutzel et al, 2016;Kristensen et al, 2020;Thomsen et al, 2021). Various methods have been used for estimating the saturation vapor pressures or saturation mass concentrations of α-pinene ozonolysis products (Ehn et al, 2014;Kurtén et al, 2016;D'Ambro et al, 2018;Buchholz et al, 2019;Peräkylä et al, 2020;Räty et al, 2021).…”

Comparison of computational and experimental saturation vapor pressures of α-pinene + O<sub>3</sub> oxidation products

“…Recently, Thomsen et al (2021) identified multiple carboxylic acids in SOA formed in α-pinene ozonolysis experiments using an ultra-high performance liquid chromatograph (UHPLC). Out of the compounds included in Thomsen et al (2021) (Bilde and Pandis, 2001;Lienhard et al, 2015;Babar et al, 2020) are given for the specific isomer, while COSMOtherm15 values (Kurtén et al, 2016) are for various other isomers. Babar et al (2020) and Kostenidou et al (2018), respectively.…”

“…Monoterpenes (C 10 H 16 ) are an abundant class of BVOCs emitted by various plants (Guenther et al, 1995). The oxidation mechanism of monoterpene reactants vary significantly, leading to products with different SOA formation capabilities (Thomsen et al, 2021). Additionally, the initial oxidant (i.e., OH, O 3 and NO 3 ) affects the SOA formation rates of the oxidation products (Kurtén et al, 2017).…”

“…For example, α-pinene, a very abundant monoterpene in the atmosphere, has been widely studied in both laboratory and field experiments (Docherty et al, 2005;Hall IV and Johnston, 2011;Hao et al, 2011;Ehn et al, 2012Ehn et al, , 2014Kristensen et al, 2014;Lopez-Hilfiker et al, 2015;McVay et al, 2016;D'Ambro et al, 2018;Huang et al, 2018;Claflin et al, 2018;Ye et al, 2019), and α-pinene oxidation, both with O 3 and OH, is efficient at producing oxygenated organic molecules and SOA. Consequently, the oxidation mechanism and potential structures of α-pinene + O 3 products have been extensively studied both experimentally and computationally (Rissanen et al, 2015;Berndt et al, 2018;Kurtén et al, 2015;Iyer et al, 2021;Lignell et al, 2013;Aljawhary et al, 2016;Mutzel et al, 2016;Kristensen et al, 2020;Thomsen et al, 2021).…”