Figure 4.
The statistically significant changes in the concentrations of OA factors after perturbation by (a) α-pinene and (b) β-caryophyllene. The experiments are sorted by average [O3] during Chamber_Af. The average [NOx] values during Chamber_Af are shown on top of the figure. The changes in concentration are the differences between measurements during Chamber_Af and extrapolated Chamber_Bf (Appendix A). A set of criteria are developed to evaluate if the changes are statistically significant and if the changes are due to ambient variation (Appendix A). Isoprene OA decreases after β-caryophyllene injection. The reason for this decrease is unclear, but likely due to the limitations of PMF analysis, which assumes constant mass spectra of OA factors over time (Sect. S3 of the Supplement).