Highly Oxidized Multifunctional Organic Compounds Observed in Tropospheric Particles: A Field and Laboratory Study

Abstract

Very recent studies have reported the existence of highly oxidized multifunctional organic compounds (HOMs) with O/C ratios greater than 0.7. Because of their low vapor pressure, these compounds are often referred as extremely low-volatile organic compounds (ELVOCs), and thus, they are able to contribute significantly to organic mass in tropospheric particles. While HOMs have been successfully detected in the gas phase, their fate after uptake into particles remains unclear to date. Hence, the present study was designed to detect HOMs and related oxidation products in the particle phase and, thus, to shed light on their fate after phase transfer. To this end, aerosol chamber investigations of α-pinene ozonolysis were conducted under near environmental precursor concentrations (2.4 ppb) in a continuous flow reactor. The chemical characterization shows three classes of particle constituents: (1) intact HOMs that contain a carbonyl group, (2) particle-phase decomposition products, and (3) highly oxidized organosulfates (suggested to be addressed as HOOS). Besides chamber studies, HOM formation was also investigated during a measurement campaign conducted in summer 2013 at the TROPOS research station Melpitz. During this field campaign, gas-phase HOM formation was found to be correlated with an increase in the oxidation state of the organic aerosol.

High-molecular-weight esters in <i>α</i>-pinene ozonolysis secondary organic aerosol: structural characterization and mechanistic proposal for their formation from highly oxygenated molecules

“…In addition, it is consistent with the findings by Mutzel et al (2015) that intact HOMs detected in the gas phase are carbonyl-containing compounds. Recent work has also established that hydroperoxides present in α-pinene/O 3 SOA are unstable and quickly convert to more stable products (Krapf et al, 2016).…”

“…The molecular characterization of secondary organic aerosol (SOA) has been a topic of interest in atmospheric chemistry for the last decades, owing to the importance of organic aerosol in air quality and climate (for a review, see Nozière et al, 2015). SOA comprises a large number of oxygenated organic compounds and is a major constituent of submicrometer atmospheric particulate matter (PM), and both biogenic (e.g., isoprene, monoterpenes, sesquiterpenes) and anthropogenic (aromatics, n-alkanes) volatile organic compounds (VOCs) serve as precursors for SOA.…”

“…Abundant biogenic VOCs in the terrestrial atmosphere are monoterpenes, having an annual global emission rate of 155 Tg with α-pinene as the major terpene emitted (Guenther et al, 2012). Several multifunctional SOA compounds, including monomers and dimers from α-pinene oxidation have been structurally identified (for a review, see Nozière et al, 2015). Recently, "extremely low-volatility organic compounds" (ELVOCs), currently termed "highly oxygenated molecules" (HOMs), originating from α-pinene ozonolysis (α-pinene/O 3 ) have been detected in both laboratory and field experiments by chemical ionization-atmospheric pressure ionization-time-of-flight (CI-APi-TOF) mass spectrometry with nitrate clustering (Ehn et al, 2012Zhao et al, 2013) and have received much attention because of their role in driving new particle formation and growth in pristine forested environments.…”

“…Recently, "extremely low-volatility organic compounds" (ELVOCs), currently termed "highly oxygenated molecules" (HOMs), originating from α-pinene ozonolysis (α-pinene/O 3 ) have been detected in both laboratory and field experiments by chemical ionization-atmospheric pressure ionization-time-of-flight (CI-APi-TOF) mass spectrometry with nitrate clustering (Ehn et al, 2012Zhao et al, 2013) and have received much attention because of their role in driving new particle formation and growth in pristine forested environments. Molecular characterization of α-pinene SOA constituents is needed to elucidate the underlying formation mechanism and establish its link with gasphase HOMs, and efforts in this direction have recently been undertaken (Mutzel et al, 2015;Zhang et al, 2015Zhang et al, , 2017Krapf et al, 2016). However, the relationship of HOMs detected in the gas phase upon α-pinene ozonolysis with stable high-molecular-weight SOA constituents is unclear, so that there is still a missing element in closing the α-pinene SOA system.…”

Formation and evolution of molecular products in α-pinene secondary organic aerosol

“…Recently, a class of extremely low-volatility gas-phase organic compounds (ELVOCs) has been identified as an important component in the α-pinene ozonolysis chemistry (13). Identification of the ELVOCs in the particle phase and elucidation of the mechanism of their formation remain key missing pieces in closing the α-pinene SOA system (14).…”