Oligomer and highly oxygenated organic molecule formation from oxidation of oxygenated monoterpenes emitted by California sage plants

Abstract

Plants emit a diverse range of biogenic volatile organic compounds (BVOCs) whose oxidation leads to secondary organic aerosol (SOA) formation. The majority of studies of biogenic SOA have focused on single or simple multicomponent BVOC mixtures thought to be representative of Northern hemispheric deciduous or mixed forest conditions. Gaps remain in our understanding of SOA formation from complex mixtures of real plant emissions in other environments. Towards the goal of understanding SOA in other regions, we conducted the first comprehensive study of SOA from oxygenated monoterpenes. These are the dominant emissions from the most common plant species in southern California's coastal sage ecosystem: black sage (Salvia mellifera) and California sagebrush (Artemisia californica). Emissions from sage plants, as well as single compounds representing their major emissions (camphor, camphene and eucalyptol), were oxidised in an Aerodyne potential aerosol mass oxidation flow reactor (PAM-OFR). The chemical composition of SOA was characterised using a high-resolution time-of-flight iodide-anion chemical-ionisation mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-I-HR-ToF-CIMS) under low- and medium-NOx conditions. SOA from oxygenated monoterpenes showed a higher-order oligomer content and a greater presence of highly oxygenated organic molecules (HOMs) than non-oxygenated monoterpenes, with HOM contributing 27 %–47 % and 12 %–14 % of SOA product signal from oxygenated and non-oxygenated monoterpenes respectively. This study highlights the potential importance of oxygenated monoterpene emissions for SOA formation in woody shrub ecosystems.