25 Aug 2023
 | 25 Aug 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Molecular Analysis of Secondary Organic Aerosol and Brown Carbon from the Oxidation of Indole

Feng Jiang, Kyla Siemens, Claudia Linke, Yanxia Li, Yiwei Gong, Thomas Leisner, Alexander Laskin, and Harald Saathoff

Abstract. Indole (ind) is a nitrogen-containing heterocyclic volatile organic compound commonly emitted from animal husbandry and from different plants like maize with global emissions of 0.1 Tg y-1. The chemical composition and optical properties of indole secondary organic aerosol (SOA) and brown carbon (BrC) are still not well understood. To address this, environmental chamber experiments were conducted to investigate the oxidation of indole at atmospherically relevant concentrations of selected oxidants (OH radicals and O3) with/without NO2. In the presence of NO2, the SOA yields decreased by more than a factor of two but the mass absorption coefficient at 365 nm (MAC365) of ind-SOA was 4.3 ± 0.4 m2 g-1, which was 5 times higher than that in experiments without NO2. In the presence of NO2, C8H6N2O2 (identified as 3-nitroindole) contributed 76 % to the all organic compounds detected by a chemical ionization mass spectrometer, contributing ~50 % of the light absorption at 365 nm (Abs365). In the absence of NO2, the dominating chromophore was C8H7O3N contributing to 20–30 % of Abs365. Indole contributes substantially to the formation of secondary BrC and its potential impact on the atmospheric radiative transfer is further enhanced in the presence of NO2, as it significantly increases the specific light absorption of ind-SOA by facilitating the formation of 3-nitroindole. This work provides new insights into an important process of brown carbon formation by interaction of two pollutants, NO2 and indole, mainly emitted by anthropogenic activities.

Feng Jiang et al.

Status: open (until 06 Oct 2023)

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Feng Jiang et al.


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Short summary
We investigated the optical properties, chemical composition, and formation mechanisms of secondary organic aerosol (SOA) and brown carbon (BrC) from the oxidation of indole with/without NO2 in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) simulation chamber. This work is one of the very few to link the optical properties and chemical composition of indole SOA with/without NO2 by simulation chamber experiments.