Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Hind A Al-Abadleh; Fatemeh Motaghedi; Wisam Mohammed; Md Sohel Rana; Kotiba A Malek; Dewansh Rastogi; Akua A Asa-Awuku; Marcelo I Guzman

doi:10.1038/s42004-022-00732-1

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Commun Chem. 2022 Sep 19;5(1):112. doi: 10.1038/s42004-022-00732-1.

Authors

Affiliations

¹ Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada. halabadleh@wlu.ca.
² Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada.
³ Department of Chemistry, University of Kentucky, Kentucky, 40506, USA.
⁴ Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, 20742, USA.
⁵ Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, 20742, USA. asaawuku@umd.edu.
⁶ Department of Chemistry, University of Kentucky, Kentucky, 40506, USA. marcelo.guzman@uky.edu.

^# Contributed equally.

Abstract

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1-7, and ionic strength 0.01-1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4-0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions.