AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Characterization of Hydroxy/Carboxyl-Nitro Compounds in SOA from Aromatic Oxidation: Implication for PM2.5
MOHAMMED JAOUI, John Offenberg, Michael Lewandowski, Amara Holder, Tad Kleindienst, EPA/ORD/NERL
Abstract Number: 244 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract SOA generated in our laboratory in the past fifteen years from the photooxidation of aromatics/NOx systems were yellow to light brown in color as compared to those generated from biogenic precursors, indicative of light absorbing organic compounds also known as brown carbon. Literature review shows that compounds containing aromatic ring(s) and/or nitro group(s) formed through atmospheric oxidation may potentially be responsible, in part, for the optical properties associated with ambient particles, therefore influencing aerosol radiative forcing.
In this study, an analytical technique developed previously in our laboratory for the identification and quantification of multifunctional compounds was extended to compounds containing at least one nitro group(s). This technique is based on silylation using BSTFA as derivatizing agent, followed by GC-MS analysis in EI and methane-CI modes. This approach was tested on standards and on SOA from photooxidation experiments of toluene, benzene, ethylbenzene, o/m/p-xylenes, m-cresol, catechol, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, naphthalene, 1-methylnaphthalene and 2-methylnaphthalene in the presence of NOX. This technique has the advantage for identifying unambiguously unknown organic compounds containing -OH/-COOH, and -NO2 group(s). For example, CI spectra contain ions at m/z (M.+ + 1), (M.+ + 29), (M.+ + 41), (M.+ - 15), (M.+ - 89), and 73 for compounds bearing only hydroxy/carboxylic groups and (M.+ - 31) for those bearing also nitro group(s). To determine the presence of these compounds in the atmosphere, PM2.5 filters collected in Research Triangle Park, NC, USA during 2003 were re-analyzed using the same analytical technique. GC-MS analysis showed the occurrence of some of these potential light absorbing compounds in chamber SOA and ambient PM2.5, indicating the impact of aromatics on brown carbon. This work describes systematically a method for identifying multifunctional compounds containing one or more nitro/hydroxyl/carboxylic groups. This is a way of supplementing optical measurements with compound identification through established, tested, reliable GC-MS methods. This isn’t a stand-alone tool, it is part of a broad suite of tools intended to address a larger problem than just aerosol composition and its relationship to optical properties.