AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Physical and Chemical Properties of 3-methyl-1,2,3-butanetricarboxylic Acid (MBTCA) Aerosol
Evangelia Kostenidou, Eleni Karnezi, Rafal Szmigielski, SPYROS PANDIS, Carnegie Mellon University, University of Patras
Abstract Number: 192 Working Group: Aerosol Physics
Abstract 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) has been proposed as the most relevant tracer compound for atmospheric terpene secondary organic aerosol (SOA) (Szmigielski et al., 2007). Recently was shown that MBTCA is produced from the oxidation of pinonic acid in the gas phase (Muller et al., 2012). However, the physical and chemical properties of MBTCA aerosol are limited. To our knowledge this is the first time that MBTCA aerosol is studied in an environmental chamber.
Aerosol MBTCA was generated through an atomizer and characterized in the Patras ICE-HT smog chamber. Atmospheric levels of OH radicals were produced by HONO photolysis under UV illumination. An Aerodyne High Resolution Aerosol Mass Spectrometer (HR-AMS) and a Scanning Mobility Particle Sizer (SMPS) measured the particle phase, while a thermodenuder was used for the volatility characterization. The gas phase was monitored by a Proton Transfer Reaction Mass Spectrometer (PTR-MS).
Some of the characteristic m/z’s in the HR-AMS mass spectrum were 39, 41, 43, 44, 53, 55, 59, 67, 69, 96, 81, 83, 99, 100, 113, 114, and 141. Even after heating the particles to 120oC for 30 s the mass spectrum remained practically the same (theta< 12$^o). The fresh MBTCA density was calculated 1.8±0.1 g cm$^(-3). The T$_(50) was estimated around 87$^oC, while an integrated volatility characterization was performed according to Karnezi et al. (2014) approach. After exposure to OH radicals and UV illumination the aerosol O:C ratio decreased while the H:C ratio increased indicating fragmentation. Positive matrix factorization (PMF) applied to the chamber experiments revealed a second less oxygenated factor after OH addition.
References:
Karnezi, E. et al (2014) Atmos. Meas. Tech., 7, 2953-2965, 2014.
Müller, L. et al. (2012) Atmos. Chem. Phys., 12, 1483-1496.
Szmigielski, R. et al. (2007) GRL, 34, 6 pp., L24811.