AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Impact of Anthropogenic Pollutants on the Formation and Fate of Highly Oxidized Multifunctional Compounds (HOMs) Formed from the Ozonolysis of alpha-pinene
MATTHIEU RIVA, Otso Peräkylä, Lauriane Quéléver, Liine Heikkinen, Olga Garmash, Mikko Äijälä, Matti Rissanen, Mikael Ehn, University of Helsinki
Abstract Number: 258 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Ozonolysis of alpha-pinene leads to formation of multifunctional gas-phase products including carboxylic acids and high molecular-weight compounds. Recently, highly oxidized multifunctional compounds (HOMs) were identified in the gas-phase in significant concentrations. These HOMs could then condense irreversibly onto aerosol surfaces to produce secondary organic aerosol (SOA). Molecular structures and formation pathways remain, however, uncertain. For instance, it has been suggested that RO$_2 + NO reaction can change composition (and possibly SOA yield) even without suppressing autoxidation to a very large degree.
In the present work, ozonolysis of alpha-pinene was systematically examined with varying NO concentrations in an indoor smog chamber. Ammonium sulfate aerosols (acidified and non-acidified) were also injected to further evaluate heterogeneous oxidations of HOMs. Experiments were conducted at room temperature (24 ± 2°C, ~ 30% of relative humidity) and atmospheric pressure in a 2-m$^3 Teflon chamber. Gaseous multi-functional organic compounds were chemically characterized using a range of time-of-flight chemical ionization mass spectrometers (HR-ToF-CIMS) with iodide (I$^−) and nitrate (NO$_3$^−) ionization. In addition, particle-phase was chemically characterized using Filter Inlet for Gases and AEROsols (FIGAERO) coupled to an I$^−-HR-ToF-CIMS and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Hundreds of compound, including highly oxidized products and oligomers, were observed in both gas- and particle-phases. The FIGAERO thermograms of individual SOA constituents formed under various conditions (i.e. NO and aerosol acidity) reveal heterogeneous processes within the oxidation of HOMs leading to increase of oligomer concentrations and SOA formation. Finally, addition of NO into the chamber perturbs formation of HOMs and produces new gas- and particle-phase products.