Abstract View
Molecular Composition and the Optical Properties of Brown Carbon Generated by the Ethane Flame
CHRISTOPHER WEST, Anusha P.S. Hettiyadura, Andrew Darmody, Gaurav Mahamuni, Justin Davis, Igor Novosselov, Alexander Laskin, Purdue University
Abstract Number: 326
Working Group: Carbonaceous Aerosol
Abstract
Atmospheric ‘Brown Carbon’ (BrC) is a complex mixture of organic compounds with diverse molecular composition and variable light-absorbing properties. Previous reports provided substantial molecular-specific information of BrC related to biomass burning emissions; however, very few studies describe BrC generated from hydrocarbon fuel combustion. The work presented here is the first study that identifies and characterizes BrC formed in the controlled flame combustion of ethane – one of the most basic hydrocarbon fuels. To understand the molecular composition and optical properties of BrC, we used an analytical platform that includes high-performance liquid chromatography (HPLC) coupled to photodiode array (PDA) detection, followed by dopant-assisted atmospheric pressure photoionization (APPI) and high-resolution mass spectrometry (HRMS). For this study, six soot samples were generated in a custom-built inverted gravity flame reactor (IGFR) at different combustion settings. The temperature of the diffusion flame was controlled by fuel dilution with Argon (up to 80% v/v) and was measured to be in the range of 1750-1950K. Basic characterization of the samples (i.e., mass loading, OC/soot ratio) was employed, followed by molecular speciation of BrC chromophores. A vast majority of BrC chromophores identified in these samples are oxygenated polycyclic aromatic hydrocarbons (O-PAHs) and unsubstituted PAHs. Nearly 90% of the total BrC absorbance was attributed to approximately equal contributions from the groups of O-PAHs, low and high molecular weight PAHs referred as PAHBaP (i.e., smaller and larger than Benzo[a]pyrene (BaP), respectively). The mass absorption coefficient (MACbulk) measured at λ350nm for the BrC fraction of aerosol emitted from hottest flame (Tmax=1946 K) was 0.49 m2/g.