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

Abstract

Abstract. Secondary organic aerosols (SOAs) formed from biogenic volatile organic compounds (BVOCs) constitute a significant fraction of atmospheric particulate matter and have been recognized to significantly affect the climate and air quality. Atmospheric SOA particulate mass yields and chemical composition result from a complex mixture of oxidation products originating from a diversity of BVOCs. Many laboratory and field experiments have studied SOA particle formation and growth in the recent years. However, a large uncertainty still remains regarding the contribution of BVOCs to SOA. In particular, organic compounds formed from sesquiterpenes have not been thoroughly investigated, and their contribution to SOA remains poorly characterized. In this study, a Filter Inlet for Gases and Aerosols (FIGAERO) combined with a high-resolution time-of-flight chemical ionization mass spectrometer (CIMS), with iodide ionization, was used for the simultaneous measurement of gas-phase and particle-phase oxygenated compounds. The aim of the study was to evaluate the relative contribution of sesquiterpene oxidation products to SOA in a springtime hemiboreal forest environment. Our results revealed that monoterpene and sesquiterpene oxidation products were the main contributors to SOA particles. The chemical composition of SOA particles was compared for times when either monoterpene or sesquiterpene oxidation products were dominant and possible key oxidation products for SOA particle formation were identified for both situations. Surprisingly, sesquiterpene oxidation products were the predominant fraction in the particle phase in some periods, while their gas-phase concentrations remained much lower than those of monoterpene products. This can be explained by favorable and effective partitioning of sesquiterpene products into the particle phase. The SOA particle volatility determined from measured thermograms increased when the concentration of sesquiterpene oxidation products in SOA particles was higher than that of monoterpenes. Overall, this study demonstrates that sesquiterpenes may have an important role in atmospheric SOA formation and oxidation chemistry, in particular during the spring recovery period.

First eddy covariance flux measurements of semi-volatile organic compounds with the PTR3-TOF-MS

“…Hellén et al (2018) claim that, due to the short atmospheric lifetime of β-caryophyllene, O 3 reactivity and secondary organic aerosol production rates are dominated by sesquiterpenes in Hyytiälä during summer. In hemiboreal forests, similar findings are reported from recent particle-phase measurements (Barreira et al, 2021).…”

“…These sesquiterpene fluxes were below the limit of detection (LoD) of the state-of-the-art instruments at that time, when considering reactivity, adhesion to surfaces, and inlet damping (Bourtsoukidis et al, 2018;Rinne et al, 2007). Recent particle phase measurements at a hemiboreal forest site in Estonia suggest that sesquiterpene oxidation products can substantially contribute to secondary organic aerosol mass (Barreira et al, 2021).…”

Oxidation product characterization from ozonolysis of the diterpene ent-kaurene

“…Another unanticipated finding was that we did not detect any dimers with oxygen numbers above 10, and the most abundant dimer signals were identified as compounds with 6-8 oxygen atoms. This is similar to the detected monomers, which is in contrast to earlier findings of monoterpenes and sesquiterpene (Qué lé ver et al, 2019;Jokinen et al, 2016;Li et al, 2021;Barreira et al, 2021;Kirkby et al, 2016;Rissanen et al, 2014), where dimers typically contained clearly more oxygen than the monomers. We can only speculate on the reasons for this, and a possible explanation is that the most oxygenated RO2 have very short lifetimes and thus terminate through unimolecular channels before colliding with another RO2.…”

Composition, concentration, and oxidant reactivity of sesquiterpenes in the southeastern U.S.

“…70 Sesquiterpenes could potentially influence the local aerosol properties despite their trace concentrations. 71 Additionally, it is possible that highly reactive sesquiterpenes, such as farnesene or β-caryophyllene may be emitted at high rates and chemically depleted prior to the measurements made here, contributing substantially to SOA formation through rapid aerosol formation within the forest canopy and low measured concentrations, which has been observed for other environments. 71 However, such a conclusion would not be supported by previous works where SOA composition has been more comprehensively measured in the southeastern US, in which organic aerosol could be explained almost completely by monoterpenes, isoprene, and other sources.…”