AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
The Captive Aerosol Growth and Evolution (CAGE) Chamber System
Don Collins, Jill Matus, NATHAN TAYLOR, Carlos Antonietti, Chance Spencer, Joshua Santarpia, Yong-Le Pan, Shanna Ratnesar-Shumate, Crystal Glen, Texas A&M University
Abstract Number: 477 Working Group: Instrumentation and Methods
Abstract The Captive Aerosol Growth and Evolution (CAGE) chamber system combines new and established design features to bridge some of the gaps in existing chamber research; informing our understanding of aerosol aging by subjecting an injected and retained population of particles to photolysis rates and gas phase composition that approach those of the immediate surroundings. Studies conducted with the chambers include assessment of bioaerosol viability, secondary organic aerosol (SOA) formation, and aqueous-phase processing. This work presents the unique design specifications and capabilities of the CAGE chamber system.
The cores of the CAGE system are two cylindrical, 1 m$^3 aerosol retention/reactor volumes. Unconventionally, these volumes operate in equilibrium with a continuous air flow isolated behind gas-permeable expanded polytetrafluoroethylene (ePTFE) membranes which constitute the vertical, circular ends of the reactor cylinders. When the gas exchange flow consists of ambient air, the reactor gas phase will closely track ambient conditions. Further, the curved cylinder wall is comprised of UV-transmitting fluorinated ethyl-propylene (FEP) film and the chambers pivot to allow full sun exposure. Combined with temperature control, these features allow the CAGE reactor volumes to mimic the ambient photo-chemical environment. Alternatively, the gas exchange flow can be fully prescribed or spiked with trace gases. Typical CAGE operation resolves the sensitivity of the aerosol aging processes in the ambient environment to isolated factors (e.g., NO$_x concentration) by spiking the gas exchange flow of one of two chambers otherwise mimicking ambient conditions. The retained aerosol injected during most experiments will be a mixture of monodisperse populations. Other CAGE features include portability to allow experiments in various ambient environments, adiabatic cloud formation, Goldberg chamber drum rotation to enhance particle and especially cloud droplet retention, equipment for generating tailored gas and aerosol samples, and analytical aerosol instrumentation including an Aerodyne HR-ToF-AMS, TDMA, SMPS and DMT-CCN.