Characterisation of Secondary Organic Aerosol Formed from the Photooxidation of Isoprene during Cloud Condensation-Evaporation Cycles (CUMULUS Project)

Friday, 19 December 2014
Chiara Giorio1, Lola Bregonzio-Rozier2, Frank Siekmann3, Brice Temime-Roussel3, Aline Gratien2, Sylvain Ravier3, Edouard Pangui2, Andrea Tapparo4, Markus Kalberer1, Reinhilde Vermeylen5, Magda Claeys5, Anne Monod3 and Jean-Francois Doussin2, (1)University of Cambridge, Department of Chemistry, Cambridge, United Kingdom, (2)Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR7583, Universités Paris-Est Créteil et Paris Diderot, Institut Pierre Simon Laplace (IPSL), Créteil, France, (3)Aix Marseille University, Marseille Cedex 03, France, (4)Università degli Studi di Padova, Department of Chemistry, Padova, Italy, (5)University of Antwerp, Department of Pharmaceutical Sciences, Antwerp, Belgium
Biogenic volatile organic compounds (BVOCs) undergo many oxidation processes in the atmosphere accompanied by formation of water-soluble compounds. These compounds could partition into atmospheric water droplets, and react within the aqueous phase producing higher molecular weight and less volatile compounds which could form new aerosol (Ervens et al., 2011).

This work investigates the formation and composition of secondary organic aerosol (SOA) from the photooxidation of isoprene and methacrolein (its main first-generation oxidation product) and the effect of cloud water on SOA formation and composition.

The experiments were performed within the CUMULUS project (CloUd MULtiphase chemistry of organic compoUndS in the troposphere) at the 4.2 m3 stainless steel CESAM chamber (Wang et al., 2011). In each experiment, isoprene or methacrolein was injected in the chamber together with HONO under dry conditions before irradiation. The experimental protocol was optimised to generate cloud events in the chamber, lasting for ca. 10 minutes in the presence of light. Gas phase compounds were analyzed on-line by a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-ToF-MS), a Fourier Transform Infrared Spectrometer (FTIR), NOx and O3 analyzers. SOA formation and composition were analysed on-line with a Scanning Mobility Particle Sizer (SMPS) and an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and off-line through sampling on filters and analysis in GC-MS and LC-MS.

We observed that during cloud formation water soluble gas-phase oxidation products readily partitioned into cloud droplets and new SOA was promptly produced. Chemical composition, elemental ratios and density of SOA were compared before, during cloud formation and after cloud evaporation.

Ervens, B. et al. (2011) Atmos. Chem. Phys. 11, 11069‑11102.

Wang, J. et al. (2011) Atmos. Measur. Tech. 4, 2465‑2494.