Recent advances in understanding secondary organic aerosol formation from ozonolysis of Δ3-carene and other monoterpenes

It is important to investigate formation, composition and properties of secondary organic aerosol (SOA) from monoterpenes in order to develop an accurate understanding of their atmospheric chemistry, impact on the aerosol budget and the effects of climate change. Δ3-Carene is one of the monoterpenes emitted in highest amounts in the boreal forest, yet only few studies have investigated the atmospheric chemistry and aerosol formation of Δ3-carene. In this work, we have investigated aerosol formation and composition of SOA from ozonolysis of Δ3-carene at different concentration levels in the AURA atmospheric simulation chamber at Aarhus University, Denmark. At low concentrations of Δ3-carene (about 10 ppb), SOA formation shows minimal temperature dependence under dry conditions. This contrasts with results from studies of Δ3-carene at higher concentrations (about 50 ppb) and studies of the structurally quite similar monoterpene a-pinene. Furthermore, we observed increased particle nucleation at higher relative humidity (about 80% RH, 10°C). Chemical analysis of the SOA found a series of carboxylic acids, in line with previous studies, with different concentration profiles over time, depending on experiment temperature. In experiments with ozonolysis of mixtures of Δ3-carene and a-pinene, we were able to identify a mixed dimer composed of molecular units from each of the precursors.