Impact of reactive uptake of oxygenated volatile organic compounds on acidic aerosols on SOA formation

SSCI-VIDE+CARE+CUB:RGM:DCA:SPR:CGO:MRVInternational audienceThe importance of the secondary organic aerosol (AOS) in the atmosphere motivate the scientific community to study their formation mechanisms. Despite the important number of studies on the formation and aging of SOA, this field remains poorly characterized.The volatile organic compounds (VOC) can be oxygenated to form the oxygenated volatile organic compounds (OVOCs) with different volatility related to a different oxygenation degree. The OVOCs with low volatility have a facility to condense on the aerosols and to form AOS. In 2006 Liggio et al had shown that the OVOCs can contribute to the AOS formation by reactive uptake. This way of AOS formation is still little studied. In our study we are interested to understand this mechanism and to study its influence and contribution on the AOS formation.The experimental concept consist to generate acid aerosol with a TSI atomizer (model 3706). A diffusion dryer (model 3062, TSI,US) was used to decrease the aerosol humidity. A differential mobility analyzer (DMA 3081, TSI, US, impactor size 0.071 cm), was placed downstream of the particle generation assembly and was set to select particles in the required size range (100 nm) The particle stream leaving the DMA was diluted with pure air to obtain a total mass of few μg m-3. It was flown into a flow tube (18 L) where it was exposed to gaseous OVOC. We tested two residence times in the flow tube (15 and 30 minutes). At the exist of the flow tube the aerosol size distribution are measured by a Scanning Mobility Particle Sizer (SMPS) and the aerosol chemical composition are measured by an aerosol mass spectrometer (C-ToF-AMS).A reaction between an acid aerosol and an epoxide (α-pinene oxide) was used to validate the experimental setup. We compare our results to the results obtained by Xu, Wen et al for the same chemical reaction. To follow the epoxide reactive uptake on the ammonium bisulfate we based us on the Sulfate/organic ratio evolution.Liggio, John, and Shao‐Meng Li. "Reactive uptake of pinonaldehyde on acidic aerosols." Journal of Geophysical Research: Atmospheres 111.D24 (2006).Xu, Wen, et al. "Acid-catalyzed reactions of epoxides for atmospheric nanoparticle growth." Journal of the American Chemical Society 136.44 (2014): 15477-15480