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Enhanced Formation of Brown Carbon from Photooxidation of 1-Methylnaphthalene in the Presence of Nitrogen Oxides, Ammonia, and Water Vapor
YUMENG CUI, Alexander Frie, Justin Dingle, Stephen Zimmerman, Isis Frausto-Vicencio, Francesca Hopkins, Roya Bahreini, University of California, Riverside
Abstract Number: 316
Working Group: Carbonaceous Aerosol
Abstract
Improved understanding of secondary organic aerosol (SOA) particles’ optical properties are needed to better predict their radiative impacts. Here, SOA were produced by reacting 1-methylnaphthalene with hydroxyl radicals (OH), under variable ammonia (NH3), nitrogen oxides (NOx), and relative humidity (RH) conditions. The resulting single scattering albedo (SSA), mass absorption coefficient (MAC) and refractive index (RI) values at λ=375 nm suggest formation of light-absorbing aerosols. Under intermediate-NOx and dry conditions, MAC values increased by a factor of two with the addition of NH3 to 0.24 m2 g-1 while with increased RH MAC further increased ~50%. Under high-NOx conditions, MAC value increased by 20% to 0.51 m2 g-1 with the addition of NH3. The highest MAC was reached under high-NOx, high NH3 and increased RH (0.69 m2 g-1). Time series of MAC showed increasing trends only in the presence of NH3, suggesting continuous formation of chromophores. Composition analysis of SOA suggests that organonitrates (ON) and other nitrogen-containing organic compounds (NOC) are potential chromophores in the 1-methylnaphthalene SOA. Formation of NOCs was observed only in the presence of NOx and NH3, and was enhanced under elevated RH. Organic mass spectra obtained by a time-of-flight Aerosol Mass Spectrometer (mAMS) were analyzed with Positive Matrix Factorization (PMF) model. More details about the correlations between 1-methylnaphthalene SOA optical properties and the factors resolved by PMF during different oxidation conditions will be presented.