Heterogeneous Nitration of Biomass Burning Aromatic Compounds and Evolution of Their Light Absorbing Properties

LAURA-HELENA RIVELLINI, Carolyn Liu-Kang, Jonathan Abbatt, University of Toronto, Canada

     Abstract Number: 48
     Working Group: Carbonaceous Aerosol

Abstract
With climate change, biomass burning (BB) emissions are occurring more frequently as a consequence of hotter and drier conditions. BB is a major source of black carbon and organic aerosols, namely brown carbon (BrC), responsible for light absorption in the ultraviolet (UV) and visible regions. Compounds such as polycyclic aromatic hydrocarbons (PAH), lignin-derived phenols or nitroaromatics are known chromophores and important BrC contributors. In order to reduce uncertainties associated with BB aerosols’ impact on climate, it is necessary to improve our understanding of BrC formation and how atmospheric processing affects their chemical and optical properties.

In this work, we focus on the evolution of the light absorbing properties of nitroaromatics formed by heterogeneous nitration of aromatic-containing BB organic aerosols (BBOA) under dark conditions. Flow tube and chamber experiments were conducted to study the reactions between low volatility phenolic compounds, furans and PAHs coated on different seeds (ammonium sulfate, organics and soot) and nitrogen dioxide (NO₂) or nitrate radicals (NO₃). Online and offline mass spectrometry was used for the chemical characterization of BrC upon exposure to NO₂/NO₃, and light absorption properties were monitored online with multiwavelength absorption measurements and offline by UV-visible spectroscopy. Surface reaction experiments of the abovementioned aromatic compounds exposed to various NO₂/NO₃ mixing ratios were also conducted and analysed offline. Finally, heterogeneous nitration of water-soluble extracts and organic aerosols generated by wood burning will also be investigated to simulate conditions closer to night-time aging of BBOA.