Characterizing the Influence of Particle Coating and Volatility on the Differential Loading Compensation Parameter from a DualSpot® Aethalometer

RYAN POLAND, John Allen, Zachary McQueen, Rawad Saleh, Geoffrey Smith, University of Georgia

     Abstract Number: 230
     Working Group: Instrumentation and Methods

Abstract
Aethalometers are widely used to measure concentrations and optical properties of black carbon (BC)-containing particles, highly absorbing combustion tracers that contribute significantly to climate change. These instruments operate by measuring the transmission of light through filters loaded with particles but are known to suffer from loading effects resulting in an underestimation of BC. In 2015, Drinovec et al. (2015) introduced DualSpot® technology, which provides a way to generate a real-time compensation parameter (k) to correct for the loading effect, using two filter spots sampling at different flow rates. Using a differential loading approach for calculating k based on the scheme of Virkkula et al. (2007), rather than the integrated loading approach of Drinovec et al. (2015), improves absorbance measurements. Here, we explore the potential use of these differential k values from a seven-wavelength AE33 aethalometer as indicators of particle coating and volatility. Specifically, we calculate a volatility factor (VF) using the ratio of extinctions from a pair of cavity ring-down spectrometers with and without a thermodenuder. We show how values of k and their wavelength dependence correlate with the VF for ambient aerosol (Athens, GA), and how these correlations may differ by season.