10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Aromatic Volatile and Intermediate Volatility Compound Oxidation with Hydroxyl and Nitrate Radicals: Night-time SOA Formation from Residential Solid Fuel Burning Emissions
SIMONE PIEBER, Urs Baltensperger, Amelie Bertrand, Joel Corbin, Josef Dommen, Rujin Huang, Felix Klein, Nicolas Marchand, Ugo Molteni, Haiyan Ni, Jay G. Slowik, Brice Temime-Roussel, Christoph Zuth, Andre S.H. Prévôt, Paul Scherrer Institute
Abstract Number: 1711 Working Group: Aerosol Chemistry
Abstract Gas-phase emissions in urban environments are often dominated by anthropogenic sources, such as combustion processes used for transport and residential heating. These emissions include monocyclic aromatics (benzene, toluene, ethylbenzene, xylenes, often collectively denoted BTEX), naphthalene and higher polycyclic aromatic hydrocarbons (PAHs), and oxygenated aromatics, such as predominantly phenolic compounds, and furans. These species are reactive towards hydroxyl radicals and have been shown to form secondary organic aerosols (SOA) induced by photochemistry. Due to their low reactivity towards ozone, oxidation of these compounds by hydroxyl radicals is both the main reactive removal and SOA formation pathway for those compounds during daytime. Their chemical processing during night-time (when hydroxyl radical concentrations are low) instead remains largely unassessed. While SOA formation from the reaction of nitrate with biogenic gases has been investigated in the past, only little information on nitrate radical initiated chemistry of anthropogenic emissions and formation of low volatility products thereof has been reported so far.
Hence, we studied the day and night-time oxidative aging of non-methane organic compounds emitted from residential solid fuel burning. We used bituminous coal to generate an emissions mix used as a model for our novel study. Emissions were diluted and injected into a Teflon smog chamber, and characterized with state-of-the-art instrumentation, including a combination of two high resolution proton transfer reaction time-of-flight mass spectrometers (PTR-ToF-MS), of which one was equipped with a fast gas-chromatography module, for the identification and quantification of the emissions. The GC module allows for the separation of isomeric compounds. In parallel we deployed a flame ionization monitor, to determine methane and the total non-methane hydrocarbons. The non-refractory particle phase was characterized with a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) equipped with a PM2.5 inlet lens, as well as a thermal desorption aerosol gas chromatograph-aerosol mass spectrometer (TAG-AMS) and offline samples, analyzed with ultra-high pressure liquid chromatography electrospray ionization Orbitrap mass spectrometry (UHPLC-ESI-Orbitrap-MS). The emissions were subjected to photochemical (hydroxyl radical) and dark (nitrate radical) oxidation in the SC.
We present and compare the oxidation of those emissions and link the volatility of the precursors and their oxidation products to the observed SOA formation. Finally, we also comment on differences in the gas-phase and particle-phase products formed in the two oxidation regimes as detected by the mass spectrometric techniques.