Modeling of carbonyl/ammonium sulfate aqueous brown carbon chemistry via UV/vis spectral decomposition

Ma, S.; Woo, Joseph L.; Fan, M.; Dai, Z.; Ferdousi, N.

Modeling of carbonyl/ammonium sulfate aqueous brown carbon chemistry via UV/vis spectral decomposition

Abstract

The proper characterization of aqueous brown carbon (BrC) species, their formation,
and their light absorbance properties is critical to understanding the aggregate effect that they
have on overall atmospheric aerosol climate forcing. The contribution of dark chemistry secondary
organic aerosol (SOA) products from carbonyl-containing organic compounds (CVOCs) to overall
aqueous aerosol optical properties is expected to be significant. However, the multiple, parallel
pathways that take place within CVOC reaction systems and the diering chromophoricity of
individual products complicates the ability to reliably model the chemical kinetics taking place. Here,
we proposed an alternative method of representing UV-visible absorbance spectra as a composite of
Gaussian lineshape functions to infer kinetic information. Multiple numbers of curves and different
CVOC/ammonium reaction systems were compared. A model using three fitted Gaussian curves
with magnitudes following first-order kinetics achieved an accuracy within 65.5% in the 205–300-nm
range across multiple organic types and solution aging times. Asymmetrical peaks that occurred in
low-200-nm wavelengths were decomposed into two overlapping Gaussian curves, which may have
been attributable to different functional groups or families of reaction products. Component curves
within overall spectra exhibited different dynamics, implying that the utilization of absorbance at a
single reference wavelength to infer reaction rate constants may result in misrepresentative kinetics
for these systems.

Title	Modeling of carbonyl/ammonium sulfate aqueous brown carbon chemistry via UV/vis spectral decomposition
Creator	Ma, S.
	Woo, Joseph L.
	Fan, M.
	Dai, Z.
	Ferdousi, N.
Publisher	Atmosphere
Academic Department	Chemical & Biomolecular Engineering
Division	Engineering
Organization	Lafayette College
Date Issued	April 7, 2020
Date Available	2020-04-13
Type	Article
Language	English
Keyword	absorbance
	modeling
	secondary organic aerosol
	brown carbon
	aqueous aerosol
Bibliographic Citation	Fan, M., et al (2020) "Modeling of carbonyl/ammonium sulfate aqueous brown carbon chemistry via UV/vis spectral decomposition." Atmosphere 11:358.
Standard Identifier	Handle 10385/7w62f855d
Standard Identifier	DOI 10.3390/atmos11040358
Permalink	http://hdl.handle.net/10385/7w62f855d
Rights Statement	Creative Commons - Attribution
Rights Holders	Ma, S.
	Woo, Joseph L.
	Fan, M.
	Dai, Z.
	Ferdousi, N.