Combining a rotating drum and cavity ring down spectroscopy for exploring atmospheric gas-particle interfaces

Poster-Academic
Poster Presentation

Prepared by C. Smith1, A. Ziegler2, E. Durke2, M. Brown3, S. Dhaniyala3, S. Farley1, J. Morris1
1 - Virginia Tech Chemistry Department, 480 Davidson Hall, 900 West Campus Dr, Blacksburg, Virginia, 24060, United States
2 - Edgewood Chemical Biological Center, 5183 Blackhawk Rd, APG, MD, 210105424, United States
3 - Clarkson University, 8 Clarkson Ave, Potsdam, NY, 13699, United States


Contact Information: cecilia1@vt.edu; 919-274-0002


ABSTRACT

A novel instrument combining particle suspensions using rotating drum technology and cavity ring down spectroscopy (RD-CRDS) has been developed for the investigation of specific molecule-particle and particle-particle interactions under atmospheric conditions. The instrument’s design allows for the creation of a well-defined and controllable atmosphere of suspended particles, analyte gases, and background gas molecules, which remains stable up to several days. Concentrations of key gas phase components and particle suspension characteristics in the main chamber can be ascertained in real time in response to a perturbation to the model atmosphere, such as the introduction of a gas-phase reactant. A stationary tube along the central axis of the drum serves multiple purposes. The tube provides the primary housing for the CRDS optics and stationary ports for introducing gases and particles in situ with rotation and monitoring. The tube extension also reduces the particle concentration along the axis, which decreases the effect of particles (scattering) on the gas-phase spectroscopy. Cavity ring down spectroscopy records mid-infrared spectra (1010 cm-1 to 860 cm-1) to determine concentrations and identifications of new gas species evolved from gas-particle chemistry. Preliminary studies have shown that polystyrene latex (Dp = 0.994 µm) and ammonium sulfate (Dp = ~100 nm) particles remain suspended for at least 22 hours while the drum rotates at 2 RPM. Initial investigation into the atmospheric life cycle of ammonia involved studying the efficiency of the monomethylamine–ammonia exchange reaction on ammonium sulfate particles. In accord with previous studies, our preliminary results show that this reaction occurs readily on suspended particles under atmospheric conditions. Overall, the new RD-CRDS approach to atmospheric science provides the opportunity to study the influence of interfacial chemistry on particle growth, aging, and re-admission of gas-phase compounds.