Origin and variability of volatile organic compounds observed at an Eastern Mediterranean background site (Cyprus)

Other literature type English OPEN
Debevec, Cécile ; Sauvage, Stéphane ; Gros, Valérie ; Sciare, Jean ; Pikridas, Michael ; Stavroulas, Iasonas ; Salameh, Thérèse ; Leonardis, Thierry ; Gaudion, Vincent ; Depelchin, Laurence ; Fronval, Isabelle ; Sarda-Esteve, Roland ; Baisnée, Dominique ; Bonsang, Bernard ; Savvides, Chrysanthos ; Vrekoussis, Mihalis ; Locoge, Nadine (2017)

More than 7,000 atmospheric measurements of over sixty C2-C16 Volatile Organic Compounds (VOCs) have been conducted at a background site in Cyprus during a 1-month intensive field campaign held in March 2015. This exhaustive dataset consisted in primary anthropogenic and biogenic VOCs, including a wide range of source-specific tracers, and oxygenated VOCs (originating from various origins) that were measured on-line by flame ionization detection/gas chromatography and proton transfer mass spectrometry. On-line submicron aerosol chemical composition was performed in parallel using an aerosol mass spectrometer. This study presents high temporal variability of VOCs and their associated sources. A preliminary analysis of their time series was performed on the basis of independent tracers (NO, CO, black carbon), meteorological data and clustering of air mass trajectories. Biogenic compounds were mainly attributed to be of local origin and showed compound-specific diurnal cycles such as daily maximum for isoprene and nighttime maximum for monoterpenes. Anthropogenic VOCs as well as oxygenated VOCs displayed higher mixing ratios under the influence of continental air masses (i.e. Western Asia) indicating that long-range transport significantly contributed to the VOC levels in the area. Source apportionment was then conducted on a database of 20 VOCs (or grouped VOCs) using a source receptor model. The positive matrix factorization and concentration field analyses were hence conducted to identify and characterize co-variation factors of VOCs that were representative of primary emissions as well as chemical transformation processes. A six-factor PMF solution was selected, namely two primary biogenic factors (relative contribution of 43 % to the total mass of VOCs) for different types of emitting vegetation; three anthropogenic factors (short-lived combustion source, evaporative sources, industrial and evaporative sources, 21 % all together), identified either of local origin but also from more distant emission zones (i.e. the south coasts of Turkey); and a last factor (36 %) associated to a regional background pollution (air masses transported both from Western and Eastern Mediterranean regions). One of the two biogenic and the regional background factors were found to be the largest contributors to the VOCs concentrations observed at our sampling site. Finally, a combined analysis of VOCs PMF factors with source apportioned organic aerosols (OA) helped to better distinguish between anthropogenic and biogenic influences on the aerosol and gas phase compositions. The highest OA concentrations were observed when the site was influenced by air masses rich in semi-volatile OA (less oxidized aerosols) originating from the Southwest of Asia, in contrast with OA factor contributions associated with the remaining source regions. A reinforcement of secondary OA formation also occurred due to intense oxidation of biogenic precursors.
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