Phase Morphology and Optical Properties of Brown Carbon Containing Aerosol Particles
Chelsea Price, JAMES F. DAVIES, Thomas Preston, Roya Bahreini,
University of California Riverside Abstract Number: 210
Working Group: Aerosol Chemistry
AbstractWildfires and biomass burning are a significant source of brown carbon (BrC) chromophores to aerosol particles into the atmosphere. These chromophores absorb light leading to atmospheric warming with a magnitude estimated to be equal an opposite to the cooling effect of scattering particles. Of particular interest are nitrated aromatic compounds because of their strong absorptive properties, formation during daytime and nighttime reactions, and water solubility. Due to their water solubility, BrC particles may act as cloud condensation nuclei and knowledge of their humidity-dependence physical and optical properties will be important to better understand their role in the atmosphere.
In this work, a linear quadrupole electrodynamic balance with a broadband light source was used to illuminate levitated aqueous brown carbon particles consisting of 4-nitrocatechol (4NC) for Mie resonance spectroscopy. The back scattered light from the particle was then used to determine the size, refractive index, and dispersion properties simultaneously. We measured the hygroscopic growth and optical properties of pure 4NC particles as well as mixtures of 4NC containing a non-absorbing inorganic component (ammonium sulfate) over a range of mixing ratios. (Price et al., Environ. Sci. Technol. 2022, 56, 7, 3941–3951). We identified the phase transitions in the mixed particles noting the onset of liquid-liquid phase separation and efflorescence. Going forwards, we will use these established methods as a basis to explore the behavior of other nitroaromatic compounds, such as 4-nitrophenol and 4-nitrobenzoic acid, as well as chamber generated BrC-SOA.