Secondary organic aerosol formation from aromatic alkene ozonolysis: influence of the precursor structure on yield, chemical composition and mechanism 

Chiappinia), E. Perraudinb),d), N. Maurina), W. Zhengb)Marchandb), B. Temime-Rousselb), A. Le Personc), F. Bernardc), G. Eyglunentb),c)Monodb), A. Melloukic), B. Picquet-Varraulta), J.-F. Doussina)

a)Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR7583, CNRS, Université Paris-Est-Créteil (UPEC) et Université Paris Diderot (UPD), Institut Pierre Simon Laplace (IPSL), Créteil, France

b)Aix-Marseille Université, CNRS, LCE UMR 7376, 13331, Marseille, France

c)ICARE (Institut de Combustion, Aérothermique, Réactivité et Environnement) CNRS (Centre National de la Recherche Scientifique) – UPR3021, 1C, Avenue de la recherche scientifique, 45071 Orléans cedex 02, France

d)Now at EPOC, UMR 5805, University of Bordeaux, CNRS, Allée Geoffroy Saint-Hilaire, 33615 Pessac Cedex, France

This work investigates the influence of the precursor chemical structure on secondary organic aerosol (SOA) formation through the study of the ozonolysis of two anthropogenic aromatic alkenes: 2-methylstyrene and indene. Experiments were carried out in three different simulation chambers: ICARE 7300L FEP Teflon chamber (ICARE, Orléans, France), EUPHORE FEP Teflon chamber (CEAM, Valencia, Spain) and CESAM evacuable stainless steel chamber (LISA, Créteil, France). For both precursors, SOA yield and growth were studied on a large range of initial concentrations (from ~60 ppbv to 1.9 ppmv) and the chemical composition of both gaseous and particulate phases was investigated at a molecular level. Gas-phase was described using FTIR spectroscopy and on-line gas chromatography coupled to mass spectrometry and particulate chemical composition was analysed i) on-line by thermo-desorption coupled to chemical ionisation mass spectrometry (TD-API-AMS) and ii) off-line by supercritical fluid extraction coupled to gas chromatography and mass spectrometry (SFE-GC-MS). The results obtained from a large set of experiments performed in three different chambers and using several complementary analytical techniques were in very good agreement. SOA yield was up to 10 times higher for indene ozonolysis than for 2-methylstyrene ozonolysis at the same reaction advancement. For 2-methylstyrene ozonolysis, formaldehyde and o-tolualdehyde were the two main gaseous phase products while o-toluic acid was the most abundant amongst six products detected within the particulate phase. For indene ozonolysis, traces of formic and phthalic acids, as well as eleven species were detected in the gaseous phase and eleven other products were quantified in the particulate phase, where phthaldialdehyde was the main product. Based on the identified products, reaction mechanisms were proposed that highlight specific pathways due to the precursor chemical structure. These mechanisms were finally compared and discussed regarding SOA formation. In the case of 2-methylstyrene ozonolysis, ozone adds mainly on the external and mono-substituted double bond, yielding only one C8- and mono-functionalized Criegee intermediate and hence more volatile products as well as lower SOA mass than indene ozonolysis in similar experimental conditions. In the case of indene, ozone adds mainly on the five-carbon-ring and di-substituted C=C double bond, leading to the formation of two C9- and bi-functionalized Criegee intermediates, which then evolve via different pathways including the hydroperoxide channel and form highly condensable first-generation products.