Particle Light Absorption Closure Analysis: BC, Soluble BrC and Dark-BrC: Case Studies from FIREX-AQ and AEROMMA

RUCHEN ZHU, Linghan Zeng, Han N. Huynh, Adam Ahern, Joshua P. Schwarz, Amy P. Sullivan, Rodney J. Weber, Georgia Institute of Technology

     Abstract Number: 431
     Working Group: Carbonaceous Aerosols

Abstract
Atmospheric aerosols directly affect the radiative balance of the atmosphere, visibility, and photochemical reactions by absorbing and scattering solar radiation. Carbonaceous species, largely from biomass burning, are a major component of light-absorbing aerosols. Light absorbing carbon can be divided into three categories - black carbon (BC), soluble brown carbon (BrC) and dark brown carbon (d-BrC, or tar BrC, or tar balls) which are thought to be mutually exclusive. Increasing prevalence of wildland and prescribed fires makes understanding the optical properties of their emissions important. We perform a closure analysis by comparing the measurement of total absorption using a three-wavelength photoacoustic spectrometer (PAS) to the sum of the various light absorbing components, including refractory BC with estimated lensing, soluble BrC and d-BrC. We use data from the extensive suite of wildfire smoke characterized during FIREX-AQ and aged smoke measured in AEROMMA. Various parameters needed to predict optical properties of the components are based on published values. We find that at high wavelengths, there is a gap between the sum of rBC and soluble BrC and the PAS and attribute this to d-BrC. We predict the characteristics of d-BrC to fill this gap and find d-BrC mass concentration is the most important parameter. We attempt to find parameters related to the smoke that can account for this variability in d-BrC concentration. At low wavelengths, we find the sum of the absorbing components exceeds the total absorption measured with the PAS and look for parameters that may be linked to the magnitude of the over-estimation to provide a physical explanation for its cause. The goal of this work is to provide a better understanding of the components contributing to aerosol light absorption in wildfire smoke.