AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Effect of OH Scavengers on the Particle Phase Composition of α-Pinene Secondary Organic Aerosol
DAVID BELL, Veronika Pospisilova, Amelie Bertrand, Dongyu S. Wang, Chuan Ping Lee, Felipe Lopez-Hilfiker, Claudia Mohr, Wei Huang, Imad El Haddad, Jay G. Slowik, Andre S.H. Prévôt, Josef Dommen, Urs Baltensperger, Paul Scherrer Institute
Abstract Number: 482 Working Group: Aerosol Chemistry
Abstract OH scavengers (e.g. H2, CO, butanol, cyclohexane) have been used to consume all of the OH radicals that are formed in the reaction between an alkene and ozone. This is advantageous because the scavenger effectively shuts down a competing oxidation pathway so the resulting gas and particle phase products result from a single oxidation process. However, the impact a scavenger has on the resulting oxidation products has not been studied in depth until recently. Recent laboratory studies have showed that some dimers are suppressed when an OH scavenger is used in the ozonolysis of β-pinene.
In this study, experiments were performed in a series of atmospheric simulation chambers and a flow tube at the Paul Scherrer Institute studying the secondary organic aerosol formed from α-pinene + O3 with various OH scavengers (butanol, cyclopentane, and cyclohexane). The particle phase products were monitored with an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF), a soft ionization technique that measures real-time, near-molecular-level SOA composition.
The main constituents in the particle phase are C10HxOy species (where x = 14, 16, and 18 and y = 3 – 10). C10H18Oy products have been identified as products from OH chemistry via OH addition to the alkene, and subsequent auto-oxidation occurring. The C10H18Oy fraction decreases by 50 - 70% when 200 ppm of butanol is present. The remaining C10H18Oy left over is y = 4, corresponding to the Criegee intermediate reacting with H2O. As a result, the monomer region demonstrates that butanol is effective at scavenging the OH produced in the reaction between α-pinene + O3. However, the dimer distribution of α-pinene SOA was completely altered when an OH scavenger was used. This was further studied with a series of flow tube experiments to gain insight about dimer formation in these systems.