Abstract View
Cloud Condensation Nuclei (CCN) Activity Analysis of Low-Hygroscopicity Aerosols Using the Aerodynamic Aerosol Classifier (AAC)
KANISHK GOHIL, Akua Asa-Awuku, University of Maryland
Abstract Number: 76
Working Group: Instrumentation and Methods
Abstract
In this research, we present a method for Cloud Condensation Nuclei (CCN) activity analysis of aerosols using an Aerodynamic Aerosol Classifier (AAC). The AAC is a novel instrument that size-selects/classifies aerosols based on their mechanical mobility. This is done by measuring the relaxation time of particles within the AAC to determine their aerodynamic diameter. Past studies have developed theoretical models for characterizing AAC-based particle classification. Furthermore, AAC has been used for numerous applications including calibration of Optical Particle Counter (OPC), determination of particle mass, effective density and shape factor, and separation of particles. However, the utility of AAC for CCN activity analysis of aerosols has not yet been explored. Traditionally, a Differential Mobility Analyzer (DMA), which classifies aerosols based on electrical mobility, is used to obtain size-resolved measurements in CCN experiments. The classification requires aerosol particles to acquire a unit charge before being subjected to an electrostatic field while they move along the DMA column. Despite the utility of a DMA-based setup, there are issues related to particle multiple charging artifacts that introduce uncertainties in measurements and CCN activity predictions. Substituting the DMA with an AAC can help minimize these uncertainties as classification using an AAC does not require particle charging. This can potentially improve aerosol size-selection and CCN activity predictions, particularly of low-hygroscopicity species. Previously, the AAC transfer function has been used for expressing the AAC resolution and uncertainties associated with particle relaxation times. Here, we extend a similar transfer function analysis to examine the variability in AAC resolution in terms of aerosol aerodynamic diameter to facilitate quantification of size-dependent uncertainties corresponding to aerosol aerodynamic diameter. This is shown to be effective for reducing disparities in size-resolved measurements, therefore increasing the accuracy in predicting CCN activity of low-hygroscopicity aerosols.