Abstract
Abstract. In the present study, campholenic aldehyde ozonolysis was performed to investigate pathways leading to specific biogenic secondary organic aerosol (SOA) marker compounds. Campholenic aldehyde, a known α-pinene oxidation product, is suggested to be a key intermediate in the formation of terpenylic acid upon α-pinene ozonolysis. It was reacted with ozone in the presence and absence of an OH radical scavenger, leading to SOA formation with a yield of 0.75 and 0.8, respectively. The resulting oxidation products in the gas and particle phases were investigated employing a denuder/filter sampling combination. Gas-phase oxidation products bearing a carbonyl group, which were collected by the denuder, were derivatised by 2,4-dinitrophenylhydrazine (DNPH) followed by liquid chromatography/negative ion electrospray ionisation time-of-flight mass spectrometry analysis and were compared to the gas-phase compounds detected by online proton-transfer-reaction mass spectrometry. Particle-phase products were also analysed, directly or after DNPH derivatisation, to derive information about specific compounds leading to SOA formation. Among the detected compounds, the aldehydic precursor of terpenylic acid was identified and its presence was confirmed in ambient aerosol samples from the DNPH derivatisation, accurate mass data, and additional mass spectrometry (MS2 and MS3 fragmentation studies). Furthermore, the present investigation sheds light on a reaction pathway leading to the formation of terpenylic acid, involving α-pinene, α-pinene oxide, campholenic aldehyde, and terpenylic aldehyde. Additionally, the formation of diaterpenylic acid acetate could be connected to campholenic aldehyde oxidation. The present study also provides insights into the source of other highly functionalised oxidation products (e.g. m / z 201, C9H14O5 and m / z 215, C10H16O5), which have been observed in ambient aerosol samples and smog chamber-generated monoterpene SOA. The m / z 201 and 215 compounds were tentatively identified as a C9- and C10-carbonyl-dicarboxylic acid, respectively, based on reaction mechanisms of campholenic aldehyde and ozone, as well as detailed interpretation of mass spectral data, in conjunction with the formation of corresponding DNPH derivatives.
Highlights
Biogenic volatile organic compounds (BVOCs) are important secondary organic aerosol (SOA) precursor compounds, owing to their significant global emission and their reactivity towards atmospheric oxidants
Campholenic aldehyde itself is a first-generation α-pinene oxidation product (Fig. 2a), which is still volatile and is expected not to influence SOA growth in α-pinene ozonolysis
The present study demonstrates that the ozonolysis of campholenic aldehyde leads to highly functionalised oxidation products, which are responsible for its high SOA formation potential
Summary
Biogenic volatile organic compounds (BVOCs) are important secondary organic aerosol (SOA) precursor compounds, owing to their significant global emission and their reactivity towards atmospheric oxidants. In the Northern Hemisphere where mixed and boreal forests dominate, monoterpenes such as αpinene, β-pinene and 3-carene are the prevailing BVOCs. In addition, other BVOCs likely serve as SOA precursors, as the observed global SOA burden cannot be explained from bottom-up approaches using laboratory-derived SOA yields from the oxidation of monoterpenes Other BVOCs likely serve as SOA precursors, as the observed global SOA burden cannot be explained from bottom-up approaches using laboratory-derived SOA yields from the oxidation of monoterpenes Hallquist et al, 2009, and references therein) Another indication for other yet unidentified and reactive BVOCs results from ozone flux measurements at boreal forest sites (Wolfe et al, 2011). Missing sinks for OH radicals between 50 % (Sinha et al, 2010) and 58 % (Nölscher et al, 2012) have been reported for OH
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