Abstract View
Measuring Humidification Effects on Ammonium Sulfate – Nigrosin Mixtures with a Novel Humidity Controlled Albedometer
TYLER CAPEK, Christian Carrico, Kyle Gorkowski, Jared Lam, James D. Lee, Allison Aiken, Timothy Onasch, Andrew Freedman, Claudio Mazzoleni, Manvendra Dubey, Michigan Technological University
Abstract Number: 362
Working Group: Instrumentation and Methods
Abstract
Water can have a significant influence on the optical properties of atmospheric particles by altering their ability to scatter and absorb sunlight. Water can condense on these particles, increasing their size and altering their overall morphology. Some absorbing particles can be hydrophobic; however, hydrophilic coatings on these particles can lead to water uptake and enhancements in both absorption and scattering. Accurate assessment of these enhancements is key for determining the particles’ impact on the climate. We have developed a cavity attenuated phase-shift albedometer (RH-CAPS-SSA), operating at 450 nm, integrated with a humidifier to study humidification effects on the optical properties of atmospheric particles. We have characterized the optical properties and hygroscopicity of two benchmark aerosol, ammonium sulfate, and nigrosin. Ammonium sulfate (AS) is a hygroscopic aerosol that scatters strongly in the visible spectrum. Nigrosin ink is used as a proxy for strongly absorbing and weakly hygroscopic atmospheric particles, providing a reproducible model particle to study and better understand the fundamental behaviors of more complex absorbing atmospheric particles such as black and brown carbon. Mixtures of nigrosin and AS can lead to a particle that is more hygroscopic than pure nigrosin and more absorbing than pure AS. We compare the measured enhancements of pure aerosol and mixtures to models incorporating Mie theory and κ-Köhler theory with an eye on characterizing the performance of the RH-CAPS-SSA and developing a model for characterizing humidified atmospheric aerosol mixtures. Enhancements in absorption were observed for each sample containing nigrosin when relative humidity was increased. For example, absorption enhancement as high as 1.12±0.02 in pure nigrosin, which compared favorably to the Mie estimate of 1.15±0.08. As relative humidity increased, we also observed increasing single scattering albedo (SSA) in each of the samples containing nigrosin.