A chamber study of secondary organic aerosol formed by ozonolysis of α-pinene in the presence of nitric oxide

The amounts of SOA and reactive oxygen species (ROS) formed by the reaction of α-pinene with ozone (O3) in the presence of nitric oxide (NO) were studied by varying the ratio of O3 to NO in a chamber under conditions that simulate the indoor environment. The particle mass was measured using a tapered element oscillating microbalance (TEOM) and a scanning mobility particle sizer (SMPS) was used to obtain particle volume distributions. The concentrations of particle-bound reactive species (ROS) were quantitatively determined from collected filters by the measuring the oxidation of dichlorofluorescin (DCFH) to a fluorescent product. The measured fluorescent intensities were converted to equivalent H2O2 concentrations. Three sets of experiments using different concentration ratios of NO/O3 were conducted. Measured steady-state, particle-bound ROS concentrations ranged from 0.58 to 6.78 nmol/m3 of H2O2. The SOA yields were examined using Odum’s SOA yield model that relates the mass of SOA formed to the mass of hydrocarbon consumed. For the condition where NO and O3 were in a concentration ratio of 0.5, the SOA yield was the highest with 22 % of α-pinene converted to SOA. Under these experimental conditions, the highest concentration of nitrate radical in these experiments would have been produced.