Looking Back and Forward – from the Environmental Chamber to Particle Loss Correction
CHEN LE, Qi Li, Ningjin Xu, Huawei Li, Don Collins, David Cocker,
University of California, Riverside Abstract Number: 452
Working Group: Aerosol Physics
AbstractMinimizing uncertainty from particle- and vapor-loss corrections are critical for accurately quantifying aerosol yield from environmental chambers. Particle wall-loss behaviors in the UCR previous-generation dual 90-m
3 collapsible chambers were dominated by electrostatic deposition and the percentage of particle wall-loss correction versus measurable mass yield was significant. For this previous set-up, the loss of particle and vapor molecules driven by the chamber surface static charge significantly interrupted the investigation of vapor wall-loss effects, especially for low SOA-formation experiments which were widely applied in vapor wall-loss characterization studies. A new-generation 120-m
3 fixed-volume indoor chamber has been constructed at UCR and it has been experimentally observed to have minimal electrostatic-driven particle wall-loss. However, with ~90% of the traditional particle wall-loss reduced, particle coagulation dynamics are no longer negligible, affecting the traditional number concentration-based particle wall-loss correction method; other previously under-represented loss processes, such as chamber dilution and vapor wall-loss become more significant. A systematic evaluation of coagulation, dilution and vapor wall-loss effects on historical and future experimental data was thus desired.
In this work, 1) the significance of particle coagulation on the traditional number-averaged correction method are re-visited for thousands of historical runs, indicating an averaged 25% over-correction of wall losses from the traditional method in nucleation experiments and up to 50% over-correction of wall losses in seeded experiments; 2) particle wall-loss processes are re-characterized for the new 120-m
3 chamber based on size-dependent mono-dispersed characterization experiments with observed losses more sensitive to particle size approaching reported patterns for other chambers with minimum electrostatic effects; 3) chamber dilution effects on particle concentration decay was evaluated using a tracer compound (perfluorohexane) in experiments and such loss becomes observable given the major reduction on particle wall-loss; 4) a new standard three-component correction process of particle-loss has been proposed and verified; 5) vapor wall-loss have been investigated by a series of seeded m-xylene oxidation experiments, implying observable SOA mass yield correction compared to the previous-generation chambers.