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.
Highlights
The atmospheric oxidation of volatile organic compounds (VOCs) in the presence of NOx results in the formation of tropospheric ozone and secondary organic aerosol (SOA)
In the study performed by Lee et al (2006b) the photo-oxidation of methyl chavicol resulted in significant SOA formation and the formation of two abundant, structurally unidentified gas phase compounds, MW 136 (C8H8O2, yield 42 ± 9 %) and MW 150 (C9H10O2, yield 23 ± 5 %), detected using proton transfer reaction mass spectrometry (PTR-MS)
SOA composition was investigated using an extensive range of instruments, including; highperformance liquid chromatography ion trap mass spectrometry (HPLC-ITMS), high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLCQTOFMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS)
Summary
The atmospheric oxidation of volatile organic compounds (VOCs) in the presence of NOx results in the formation of tropospheric ozone and secondary organic aerosol (SOA). There have been few reports in the literature which have investigated the atmospheric fate of methyl chavicol, including gas-phase degradation, SOA formation, composition and yields. In the study performed by Lee et al (2006b) the photo-oxidation of methyl chavicol resulted in significant SOA formation (yield 40 %) and the formation of two abundant, structurally unidentified gas phase compounds, MW (molecular weight, g mol−1) 136 (C8H8O2, yield 42 ± 9 %) and MW 150. SOA composition was investigated using an extensive range of instruments, including; highperformance liquid chromatography ion trap mass spectrometry (HPLC-ITMS), high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLCQTOFMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS)
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