Enhanced Light Absorption of Levitated Droplets of Methoxyphenols upon Uptake and Complexation of Benzoquinone

AHMADRAZA CHAUDHARY, Micah Miles, Colton Calvert, Elijah Schnitzler, Oklahoma State University

     Abstract Number: 218
     Working Group: Aerosol Chemistry

Abstract
Biomass burning is one of the major sources of light absorbing organic aerosol, or brown carbon (BrC), in the atmosphere. These aerosols influence the radiative balance of the atmosphere by absorbing and scattering sunlight, particularly in the visible and near-ultraviolet region, or altering cloud nucleation processes. Previously, we have shown that the light absorption of a representative methoxyphenol from biomass burning, i.e., guaiacol, can be enhanced in bulk solutions and thin films through intermolecular interactions with quinones that act as electron acceptors to form non-covalent complexes. Quinones are known to form in the atmosphere from the gas-phase OH-initiated oxidation of aromatic precursors. Here, we extend this effort to explore the role of intermolecular interactions in the light absorption of methoxyphenols by monitoring the absorbance of acoustically levitated micrometer-scale droplets upon exposure to gas-phase benzoquinone. Droplet size and evaporation are monitored by photography and image analysis. Droplet absorbance is measured using a broadband light-source and miniature grating-based spectrometer coupled to the acoustic levitator. The droplets are exposed to varying mixing ratios of benzoquinone, based on its sublimation vapor pressure, by flowing gas through a sealed chamber that encloses the levitator. Upon uptake of gaseous benzoquinone to the droplets of methoxyphenols, absorbance was found to increase, attributed to complexation. Varying programs of benzoquinone exposure, i.e., decreasing mixing ratio in time, were explored. These results have implications for the impacts of abundant methoxyphenol emissions of biomass burning on air quality, visibility, and climate.