Acyclic Terpenes Reduce Secondary Organic Aerosol Formation from Emissions of a Riparian Shrub

Abstract

Terrestrial vegetation is a major global source of atmospheric secondary organic aerosol (SOA) through oxidation of biogenic volatile organic compound (BVOC) emissions. Climate change is altering the composition of BVOC emissions by increasing the prevalence of plant stress conditions, such as frequency and intensity of herbivorous insect outbreaks. The impact this will have on SOA formation is unknown. This laboratory study investigated the influence of aphid herbivory (Uroleucon macolai) on SOA formation from emissions of a common riparian shrub in California, Baccharis salicifolia (Asteraceae). Aphid herbivory increased the relative contribution of β-ocimene and decreased the relative contribution of β-guaiene in the BVOC emission profile. These effects on BVOC emissions did not translate to a significant aphid effect on SOA mass yields. However, for both control and aphid experiments, the fraction of total acyclic monoterpenes in the BVOC emission profile was correlated with reduced SOA mass yield. This is the first study to demonstrate a clear reduction in SOA mass yield as the proportion of acyclic terpenes in a complex BVOC mixture increased. These findings highlight the importance of better understanding acyclic terpene chemistry in the atmosphere to improve predictions of SOA in both current and future climates.