Atmospheric aerosols impact transmitted solar radiation, which in turn affects the heat trapped in the atmosphere and the climate. It is important to understand the net radiative forcing of aerosols, including the impact of the reacted products, such as brown carbon and SOA, in order to improve regional and global climate models.<br/>In this study we used the Chamber for Experimental Multiphase Atmospheric Simulation (CESAM) at LISA to perform experiments with the oxygenated aromatic compound, syringol in the droplet phase. Syringol is one of a number of oxygenated aromatic compounds shown to produce brown carbon in the presence of hydroxyl radicals and irradiation. Aerosol absorptivity was measured using an online system to extract water soluble aerosol components and record UV/visible absorbance and total organic carbon loading. We observed brown carbon formation (defined as absorbance 365 nm) with and without the presence of the hydroxyl radical. Syringol formed brown carbon in irradiated, deliquesced ammonium sulfate aerosol. Aerosol chemical composition was observed using HR-AMS. Preliminary analysis of the aerosol mass spectra indicate that products were similar in the conditions with and without OH radicals.<br/>Bulk experiments were performed in order to investigate the products of the cloud chamber experiments. Performed in small vials, solutions of syringol and ammonium sulfate, with and without hydrogen peroxide to act as a hydroxyl radical, were aged in the dark. Absorbance spectra and mass spectra via an APCI-MS were collected. The results of the chamber experiments were successfully replicated, and mass spectra revealed the presence of a dimer in each of the aged spectra. This work supports the previously proposed mechanism of oxidation and oligomerization involving a phenoxy radical but opens the possibility that syringol is capable of brown carbon formation without additional oxidants, depending on the wavelengths of radiation present.

Secondary organic aerosol production from photochemical reactions of syringol in cloud mimics

ACS Spring 2022

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