Simulation chamber studies on the atmospheric oxidation of skatole

Skatole (C₉H₉N) is an odour-producing member of the indole family and is known to be emitted from animal excreta. It is a common emission from animal husbandry due to the practice of spreading slurry and manure as an organic fertiliser. Little is known about the atmospheric reactivity of skatole with ozone (O₃), the hydroxyl radical (OH) and the nitrate radical (NO₃), or the potential impacts of the oxidation products on air quality and climate. 

A series of atmospheric simulation chamber experiments were performed at the Irish Atmospheric Simulation Chamber (IASC) to study the atmospheric reactivity of the gas-phase reaction of skatole with O₃, OH and NO₃ to determine the kinetics, products and the potential for SOA formation. The rate coefficients were determined using the relative rate method.

A time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) was operated with benzene and iodide as the reagent ions. Benzene allows for the detection of hydrocarbons, aromatic compounds and nitrogen heterocycles, so it was used to detect skatole and the initial oxidation products formed. Iodide is more suited to detecting highly oxygenated compounds and was used to identify higher generation oxidation products formed in the latter stages of the reactions. A scanning mobility particle sizer (SMPS) was used to monitor the formation of secondary organic aerosols (SOA), which were also chemically analysed by ToF-CIMS fitted with a Filter Inlet for Gases and AEROsols (FIGAERO).

The results from this series of experiments provide new information regarding the atmospheric reactivity of skatole, providing a greater understanding of the impact of emissions from the practice of using slurry and manure as organic fertilisers on air quality and climate.