New particle formation from the oxidation of direct emissions of pine seedlings

Our results demonstrate that OH-initiated oxidation of VOCs plays an important role in the nucleation process during the initial new particle formation stage. The highest average particle formation rate of 360 cm⁻³ s⁻¹ was observed for the OH-dominated nucleation events and the lowest formation rate of less than 0.5 cm⁻³ s⁻¹ was observed for the case with only O₃ present as an oxidant. In contrast to the particle formation process, ozonolysis of monoterpenes appears to be much more efficient to the aerosol growth process following nucleation.

Higher contributions of more oxygenated products to the SOA mass loadings from OH-dominated oxidation systems were found as compared to the ozonolysis systems. Comparison of mass and volume distributions from the aerosol mass spectrometer and differential mobility analyzer yields estimated SOA effective densities of 1.34±0.06 g cm⁻³ for the OH+O₃ oxidation systems and 1.38±0.03 g cm⁻³ for the O₃ dominated chemistry.