Secondary organic aerosol formation and composition from the photo-oxidation of methyl chavicol (estragole)

Abstract

Abstract. The increasing demand for palm oil for uses in biofuel and food products is leading to rapid expansion of oil palm agriculture. Methyl chavicol (also known as estragole and 1-allyl-4-methoxybenzene) is an oxygenated biogenic volatile organic compound (VOC) that was recently identified as the main floral emission from an oil palm plantation in Malaysian Borneo. The emissions of methyl chavicol observed may impact regional atmospheric chemistry, but little is known of its ability to form secondary organic aerosol (SOA). The photo-oxidation of methyl chavicol was investigated at the European Photoreactor chamber as a part of the atmospheric chemistry of methyl chavicol (ATMECH) project. Aerosol samples were collected using a particle into liquid sampler (PILS) and analysed offline using an extensive range of instruments including; high-performance liquid chromatography mass spectrometry (HPLC-ITMS), high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLC-QTOFMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The SOA yield was determined as 18 and 29% for an initial VOC mixing ratio of 212 and 460 ppbv (parts per billion by volume) respectively; using a VOC:NOx ratio of ~5:1. In total, 59 SOA compounds were observed and the structures of 10 compounds have been identified using high-resolution tandem mass spectrometry. The addition of hydroxyl and/or nitro-functional groups to the aromatic ring appears to be an important mechanistic pathway for aerosol formation. This results in the formation of compounds with both low volatility and high O:C ratios, where functionalisation rather than fragmentation is mainly observed as a result of the stability of the ring. The SOA species observed can be characterised as semi-volatile to low-volatility oxygenated organic aerosol (SVOOA and LVOOA) components and therefore may be important in aerosol formation and growth.

Urban organic aerosol composition in Eastern China differs from North to South: Molecular insight from a liquid chromatography-Orbitrap mass spectrometry study

“…C6H8O7 was identified as citric acid in the pollen sample and mountain particle sample in previous studies (Fu et al, 2008;Wang et al, 2009;Jung and Kawamura, 2011) and C9H8O4 are probably homophthalic acid derived from e.g. estragole (Pereira et al, 2014). For the Guangzhou− samples, besides the formulas of C8H6O4 and C6H8O7 discussed above, C4H6O4…”

“…According to previous studies, C8H6O4, C7H6O2 and C7H6O3 are suggested to be phthalic acid, benzoic acid and monohydroxy benzoic acid, respectively, which are derived from naphthalene (Kautzman et al, 2010;Riva et al, 2015;Wang et al, 2017;He et al, 2018;Huang et al, 2019). C8H8O2 and C8H8O3 are likely 4-hydroxy acetophenone and 4-methoxybenzoic acid which could be derived from estragole (Lee et al, 2006;Pereira et al, 2014). For the Shanghai− samples, besides C8H6O4, C7H6O3 and C7H6O2, formulas of C6H8O7 and C9H8O4 with DBE values of 3 and 6 were observed with high peak abundances.…”

Online molecular characterisation of organic aerosols in an atmospheric chamber using extractive electrospray ionisation mass spectrometry

“…As configured, the sampling setup enables a blank and chamber measurement to be obtained in a 7 min cycle, a substantially higher time resolution than most other semicontinuous sampling methods (Bateman et al, 2009;Pereira et al, 2014) or collection onto filters. It is comparable to the recent highly time-resolved particle-into-liquid-sampling measurements of Zhang et al (2015).…”

“…A number of recent studies have therefore developed online or semi-continuous atmospheric-pressure ionisation (API) MS techniques (Bateman et al, 2009;Brüggemann et al, 2015;Clark et al, 2014;Nah et al, 2013;Pereira et al, 2014;Vogel et al, 2013;Zhang et al, 2015;Zhao et al, 2017b). In this paper, we focus on the application of one such approach to organic aerosol analysis, namely extractive electrospray ionisation (EESI) MS.…”

Characterization of aerosol nitroaromatic compounds: Validation of an experimental method

“…A literature review shows that polar nitroaromatic compounds (NACs) are partially responsible for optical properties of ambient urban particles, thereby influencing their aerosol radiative forcing . Nitroaromatic compounds are typically associated with products from aromatic oxidations, biogenic oxidations, and biomass burning . In addition, a broad range of NACs have been detected in chamber irradiations of these precursors, as well as from field samples .…”