Effect of Chemical Aging by Ammonia on the Molecular Composition and Yield of Napthalene and Diesel Photooxidation Secondary Organic Aerosol
TRAN B NGUYEN, Julia Laskin, Alexander Laskin, Sergey A Nizkorodov
University of California Irvine
Abstract Number: 29
Working Group: Carbonaceous Aerosols in the Atmosphere
Last modified: March 22, 2011
The photooxidation of gas-phase emissions from diesel exhaust may substantially contribute to secondary organic aerosol (SOA) formation in urban areas. The volatile component of diesel exhaust is a mixture of unburned fuel containing alkanes and polycyclic aromatic hydrocarbons, of which naphthalene (C10H8) is the primary constituent. In the presence of gas-phase ammonia (NH3), abundant in regions like California’s San Joaquin Valley, the SOA from anthropogenic sources are chemically aged, altering the chemical composition and yields. In particular, the SOA may contain a higher fraction of organic nitrogen compounds, most of which remain uncharacterized and may be carcinogenic (e.g. nitronaphthalenes). This work will discuss the chemical composition of SOA generated from the photooxidation of a diesel mixture and naphthalene, in the presence and absence of NH3. The SOA was aged with NH3 in dark and photolytic conditions. Organic oxygen and nitrogen species were speciated with high-resolution nanospray desorption ionization (nano-DESI) mass spectrometry. The yields from both SOA precursors were measured to be substantially different in the presence and absence of NH3. Multistage tandem mass spectrometry (MSn) was used to obtain information on chemical functional groups for select compounds and to aid in molecular assignment.