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

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).