10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Impact of NOx on Secondary Organic Aerosol (SOA) Formation from α-pinene and β-pinene Photo-Oxidation: The Role of Organic Nitrates
Iida Pullinen, SEBASTIAN H. SCHMITT, Mehrnaz Sarrafzadeh, Sungah Kang, Patrick Schlag, Stefanie Andres, Einhard Kleist, Thomas F. Mentel, Franz Rohrer, Monika Springer, Ralf Tillmann, Jürgen Wildt, Cheng Wu, Defeng Zhao, Andreas Wahner, Astrid Kiendler-Scharr, Forschungszentrum Jülich
Abstract Number: 745 Working Group: Aerosol Chemistry
Abstract Impacts of nitrogen oxides (NOX) on the formation of gas phase organic nitrates (ON) and subsequent Secondary Organic Aerosol (SOA) mass formation were investigated in a constantly stirred tank reactor. This work focuses on understanding the mechanisms that results in suppression of SOA mass formation from α-pinene and β-pinene photo-oxidation in the presence of high NOx concentrations. Here we will demonstrate that ON formation alone cannot explain this NOx impact.
Effective uptake coefficients (γeff ) were measured for Highly Oxidized Multifunctional molecules (HOM), which has been found to be dependent on the number of oxygen atoms in the respective HOM. It has been observed that HOM with more than 6 O-atoms were efficiently lost on particles while the loss of HOM containing more than 8 O-atoms, was collision limited. There was no systematic difference between γeff measured for HOM-organic nitrates (HOM-ON) and other monomer termination products such as ketones, alcohols or hydroperoxides. This similarity was attributed to the multifunctional character of the HOM. Since both number and character of most functional groups in monomer HOM with the same precursor HOM-peroxy radical are identical, the vapor pressures of such HOM are within the same range. Thus the suppressing effect of NOX on SOA formation cannot be explained by the production of HOM-ON replacing other monomer termination products of peroxy radical – peroxy radical reactions.
Comparison of the fraction of organic bound nitrate (OrgNO3) stored in potential particle precursors to the fraction of OrgNO3 in the particles, revealed a substantial lack of OrgNO3 in the particle phase. This suggests a strong sink for organic nitrates in the particles. This sink could be due to hydrolysis which forms either HNO3 or an organic rest. Evaporation of HNO3 formed by hydrolysis of HOM-ON could possibly explain the missing OrgNO3 in the particle phase but not the 20-30 % lower SOA yields in presence of high NOX concentrations.