10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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The Effect of Gasoline Car Exhaust on the Photochemistry of α-Pinene
EETU KARI, Liqing Hao, Sini Isokääntä, Arttu Ylisirniö, Ari Leskinen, Pasi Yli-Pirilä, Celia Faiola, Santtu Mikkonen, Annele Virtanen, University of Eastern Finland
Abstract Number: 675 Working Group: Aerosol Chemistry
Abstract Biogenic and anthropogenic emission sources emit particles and volatile organic compounds (VOCs) into the atmosphere. Due to the presence of biogenic and anthropogenic emissions in many locations at the same time, potential interactions between the compounds emitted from these two sources has raised particular scientific interest. To clarify the biogenic-anthropogenic interactions, controlled laboratory studies with real emission sources are required. The laboratory studies with real emission sources represent better the complexity of these interactions than the studies with only pure standards, but still allow controlled conditions to investigate the processes in systematic way. In this work, we conducted an environmental chamber study to explore possible anthropogenic-biogenic interactions between a modern gasoline car (VW Golf 1.2 TSI) exhaust and α-pinene under atmospherically relevant conditions.
To investigate the effect of gasoline car exhaust on α-pinene photochemistry, we conducted three kinds of experiments: 1) experiments with only diluted gasoline car exhaust, 2) experiments with α-pinene and diluted gasoline car exhaust, 3) experiments with α-pinene and ammonium sulphate (AS) particles. In experiment type 3) the VOC/NOx ratio was adjusted so that it was comparable to experiment types 1) and 2). Both gas- and particle phases were monitored using Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS), Chemical Ionization Atmospheric Pressure interface Time-of-Flight Mass Spectrometer (CI-APi-ToF-MS) with acetate ionization, Aerosol Mass Spectrometer (SP-AMS), and Scanning Mobility Particles Sizer (SMPS).
We found that depending on the experiment in experiment type 1) gasoline car exhaust produced SOA and the formed SOA mass varied due to the changes in exhaust gas composition. From PTR-ToF-MS data, we were able to identify 18 SOA precursors whose reactions with OH-radicals explained 17%-64% from the observed SOA formation depending on the experiment indicating that some important SOA precursors, such as SVOCs, were not detectable by PTR-ToF-MS. In the experiment type 2) we were able to separate 4 factors from particle phase data measured by AMS using positive matrix factorization (PMF) method: HOA factor that was originated from car exhaust, mixed LVOOA factor that was produced by SOA originated from the photochemistry of car exhaust and α-pinene, α-pinene SVOOA factor, and α-pinene LVOOA factor. From PMF results we were able to estimate the formed SOA mass from car exhaust in experiment type 2), when both car exhaust and α-pinene were present in the chamber during the photo-oxidation. After subtracting car exhaust SOA from α-pinene SOA, we were able to conclude that the other compounds than NOx in gasoline car exhaust did not have a significant effect on SOA yield of α-pinene, and that SOA formed from α-pinene photo-oxidation dominated the total SOA mass in each experiment.
The results of this study indicate that in environments, where gasoline car exhaust is mixed with α-pinene, the photochemistry of α-pinene is significantly affected only by NOx. These results demonstrated also the need to study the car exhaust emissions with the instruments that can quantitatively measure SVOCs in order to fully understand the SOA formation from gasoline exhaust.