AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Secondary Organic Particle Growth Under Different Conditions in a Flow Tube Reactor
YUE ZHANG, Scot Martin, Franz Geiger, Mona Shrestha, Harvard University
Abstract Number: 769 Working Group: Aerosol Chemistry
Abstract A flow tube reactor was developed and used to simulate secondary organic particle formation from alpha-pinene ozonolysis under different reactants concentration conditions. The flow tube was designed to induce turbulence and mixing of the reactants. The alpha-pinene and ozone were injected into the flow tube reactor in different concentrations ranging from 0.125 ppm (3.08×10^12 molec cm^-3) to 10 ppm (2.5×10^14 molec cm^-3) for alpha-pinene and 0.10 ppm (2.5×10^12 molec cm^-3) to 500 ppm (1.2×10^16 molec cm^-3) for ozone.
The size distributions of the secondary organic particles were studied using a Scanning Mobility Particle Sizer (SMPS). The number concentration of the particles increased from a 0 to (1.26±0.02)×10^7 cm^-3, and the mass concentration increased from 0 to (4.0±0.1)×10^5 ug m^-3. Changes in the particle number concentrations and size distributions suggested that the growth mechanisms of the particles may be different at different precursor concentrations. As an example, for an alpha-pinene concentration of 3.08×10^12 molec cm^-3 reacted with excess ozone, the measured particle mode diameter was 25 nm and both coagulation and condensational growth were significant. When the alpha-pinene concentration was increased to 2.5×10^14 molec cm^-3, the particle mode size increased to 240 nm and coagulation between particles became the dominant growth mechanism. This result shows that the dominant particle growth mechanism can be shifted between condensation and coagulation, which may be useful for studying the particle growing process and whether particles produced from the same precursors have different properties when they grow from different mechanisms.