Enhanced SOA Formation from Mixtures of VOCs
Principal Investigators: John Shilling
Participants: Naruki Hiranuma and Chen Song
Collaborators: Lynn Russell and Shang Liu of the University of California, San Diego; Mikhail Pekour; and Dan Cziczo.
Comparison of the measured SOA particle mass (blue bars) formed during the dark ozonolysis of mixtures of α-pinene and cyclohexene to model result assuming a separate (solid bars) or mixed (dashed bars) particle phase. Predicted particle-phase α-pinene mass is shown in red, cyclohexene mass is shown in green. Enlarge Image
The goal of this project was to determine whether SOA formation from mixtures of VOCs could be predicted based on techniques currently employed by SOA models. First, experiments were conducted to measure the SOA yield from the dark ozonlysis of a-pinene and cyclohexene under atmospherically relevant conditions. These experiments on the pure compounds served as a baseline for experiments investigating SOA formation from mixtures of cyclohexene and α-pinene. Using the yield data obtained for the pure compounds, we predict the results of the mixture experiments under two conditions: 1) α-pinene and cyclohexene SOA are fully miscible and 2) α-pinene and cyclohexene form separate phases. Note that most atmospheric models typically assume condition 1; SOA species are miscible in each other. Comparisons of the predicted results with the experimental data (see Figure) show that SOA yields are better approximated assuming full miscibility. However, experimentally measured SOA mass exceeded that expected from partitioning theory, even when assuming full miscibility, by an average of 30 percent We attribute this enhanced SOA formation to reactive uptake, which is not currently included in most SOA models.