Abstract
Volatile organic compounds (VOCs) play a key role in the formation of ozone and secondary organic aerosol, the two most important air pollutants in Sydney, Australia. Despite their importance, there are few available VOC measurements in the area. In this paper, we discuss continuous GC-MS measurements of 10 selected VOCs between February (summer in the southern hemisphere) and June (winter in the southern hemisphere) of 2019 in a semi-urban area between natural eucalypt forest and the Sydney metropolitan fringe. Combined, isoprene, methacrolein, methyl-vinyl-ketone, α-pinene, p-cymene, eucalyptol, benzene, toluene xylene and tri-methylbenzene provide a reasonable representation of variability in the total biogenic VOC (BVOC) and anthropogenic VOC (AVOC) loading in the area. Seasonal changes in environmental conditions were reflected in observed BVOC concentrations, with a summer peak of 8 ppb, dropping to approximately 0.1 ppb in winter. Isoprene, and its immediate oxidation products methacrolein (MACR) and methyl-vinyl-ketone (MVK), dominated BVOC concentrations during summer and early autumn, while monoterpenes comprised the larger fraction during winter. Temperature and solar radiation drive most of the seasonal variation observed in BVOCs. Observed levels of isoprene, MACR and MVK in the atmosphere are closely related with variations in temperature and photosynthetically active radiation (PAR), but chemistry and meteorology may play a more important role for the monoterpenes. Using a nonlinear model, temperature explains 51% and PAR 38% of the isoprene, MACR and MVK variation. Eucalyptol dominated the observed monoterpene fraction (contributing ~75%), with p-cymene (20%) and α-pinene (5%) also present. AVOCs maintain an average concentration of ~0.4 ppb, with a slight decrease during autumn–winter. The low AVOC concentrations observed indicate a relatively small anthropogenic influence, generally occurring when (rare) northerly winds transport Sydney emissions to the measurement site. The site is influenced by domestic, commercial and vehicle AVOC emissions. Our observed AVOC concentrations can be explained by the seasonal changes in meteorology and the emissions in the area as listed in the NSW emissions inventory and thereby act as an independent validation of this inventory. We conclude that the variations in atmospheric composition observed during the seasons are an important variable to consider when formulating air pollution control policies over Sydney given the influence of biogenic sources during summer, autumn and winter.
Highlights
Volatile organic compounds (VOCs) are a group of carbon-based gases emitted by biological and anthropogenic sources that are characterised by their high vapour pressure at ambient temperatures [1,2,3]
1.4 day Figure 3 presents measurements of targeted anthropogenic compounds and Figure 4 presents an overview of the targeted biogenic compounds measured during COALAJOEYS
The maximum concentrations of biogenic VOC (BVOC) were observed in summer, while the anthropogenic VOC (AVOC) concentrations peaked in the colder months
Summary
Volatile organic compounds (VOCs) are a group of carbon-based gases emitted by biological and anthropogenic sources that are characterised by their high vapour pressure at ambient temperatures [1,2,3]. Anthropogenic VOCs (AVOCs) are important in urban environments, and in fire-prone regions of the world (such as Australia), vegetation fires can be a large, irregular, source of VOCs in the atmosphere [7,8,9]. Both BVOCs and AVOCs are important drivers of air quality since they are precursors in the formation of ozone [10,11] and fine particulate matter [12]. These react with NO2 , generating ozone and recycling the NO into NO2. These oxidised products continue the reaction chain, producing secondary organic aerosols [13,14,15]
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