Secondary organic aerosol formation from the ozonolysis of 2-carene and 3-carene

The atmospheric degradation of terpenes in the remote areas such as those with coniferous forests is known to lead to the formation and growth of atmospheric new particles. 2-carene and 3-carene have been reported to be present in number of such areas. Hence, their oxidation may represent an important source of secondary organic aerosols in some specific regions. 2-carene and 3-carene possess a structure of endocyclic double bonds which make them reactive toward ozone under atmospheric conditions. We have conducted a study on the reactions of ozone with 2-carene and 3-carene using a flow reactor dedicated to the investigation of secondary organic aerosol (SOA) formation. The reactor is equipped with an ozone generator and a movable injector which allows the reaction to occur within a short time range (typically 17 - 48 seconds). This enables us to investigate the initial steps of the SOA formation. In a first series of experiments, we have determined the rate constant for the reaction of ozone with 3-carene under pseudo-first-order conditions. The rate constant value measured was 3.8 x 10-17 molecule-1s-1, at 298 K, in agreement with the literatures and simulation chamber experiments. We have then investigated the SOA formation from the ozonolysis of 2-carene and 3-carene. By adjusting the residence time and initial concentration of carenes and ozone, number concentration of SOA have been measured for short reactions times and low concentrations of reactants. Nucleation thresholds of 2-carene and 3-carene were extracted from the plots of log N = f(Δ[Carenes]).