Development and Characterization of a Hydration Spectrometer (HySpec) System for Studying Aerosol Cloud Interactions

OGOCHUKWU ENEKWIZU, Ernie R. Lewis, Arthur J. Sedlacek, Brookhaven National Laboratory

     Abstract Number: 342
     Working Group: Instrumentation and Methods

Abstract
Aerosol-cloud interactions contribute the largest uncertainties to estimates of the Earth’s energy budget because of the poor quantification of fundamental microphysical and chemical processes. A key process is the formation of cloud residuals – aerosol particles that undergo cloud processing and are left behind after cloud drop evaporation. These aerosol particles reenter the atmosphere with different microphysical, chemical, and optical properties than the cloud condensation nuclei (CCN) that formed the cloud drop and thus interact with incoming solar radiation or influence clouds differently. The measurement of cloud residuals is, however, challenging and often limited to either aircraft campaigns or mountain site stations that employ a counterflow virtual impactor (CVI) to separate the generally larger cloud residuals from smaller aerosol particles based on their inertia. Here, we integrate a pumped CVI (PCVI), developed for laboratory applications, with a modified CCN counter to isolate and sample cloud residuals in a controlled laboratory setting. Dry aerosol particles introduced to the CCN-PCVI, which we refer to as a Hydration Spectrometer system, are first exposed to supersaturation conditions in the CCN counter that will cause some particles to activate. The resulting population of cloud droplets and non-activated particles are immediately drawn into the PCVI, where a particle-free flow of gas directed opposite the particle-laden flow provides a controllable means of separating the non-activated aerosol particles while allowing cloud droplets to be transmitted. Cloud droplets exiting the PCVI are dried prior to subsequent analysis, forming residuals, and their microphysical and optical properties are quantified. We report the efficacy and performance of the Hydration Spectrometer system for different particle types and sizes over a range of flow and supersaturation conditions.