Showing papers by "Mary K. Gilles published in 2020"

Optical properties and composition of viscous organic particles found in the Southern Great Plains

Abstract: . Atmospheric high viscosity organic particles (HVOP) were observed in samples of ambient aerosol collected on April and May 2016 in the Southern Great Plains of the United States. These particles were apportioned as either airborne soil organic particles (ASOP) or tar balls (TB) from biomass burning based on spetro-microscopic imaging and assessment of meteorological records of smoke and precipitation data. Regardless of their apportionment, the number fractions of HVOP were positively correlated (R2 = 0.85) with increased values of Angstrom absorption exponent (AAE) measured in-situ for ambient aerosol at the site. Extending this correlation to 100 % HVOP yields an AAE of 2.6, similar to previous literature reports of the class of light absorbing organic particles known as brown carbon (BrC). Although there are chemical similarities between ASOP and TB, they can be distinguished based on composition inferred from near edge absorption X-ray fine structure (NEXAFS) spectroscopy. ASOP were distinguished from TB based on their average −COOH/C=C and −COOH/COH peak ratios, with ASOP having lower ratios. NEXAFS spectra of filtered soil organic brine particles nebulized from field samples of standing water deposited after rain were consistent with ASOP when laboratory particles were generated by bubble bursting at the air-organic brine interface. However, particles generated by nebulizing the bulk volume of soil organic brine had particle composition different from ASOP. These observations are consistent with the raindrop generation mechanism responsible for ASOP emissions in the area of study. In contrast, nebulized samples carry with them higher fractions soil inorganics dissolved in the bulk volume of soil brine that are not aerosolized by the raindrop mechanism. Our results support the bubble bursting mechanism of particle generation during rainfall resulting in the ejection of soil organics into the atmosphere.

Microanalysis of Primary Biological Particles from Model Grass over Its Life Cycle

Abstract: Airborne biological aerosols are an integral part of the atmosphere–biosphere interface and significantly impact the environment and Earth’s climate. Primary biological particles such as fungal spo...