AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Measurement of the Sensitivity of Biogenic SOA Formation under Ambient Conditions to Anthropogenic Factors Using a New Captive Aerosol Growth and Evolution Chamber System during the Southern Oxidant and Aerosol Study
Don Collins, NATHAN TAYLOR, Jill Matus, Carlos Antonietti, Chance Spencer, Robert Griffin, Yu Jun Leong, Basak Karakurt Cevik, Texas A&M University
Abstract Number: 436 Working Group: Aerosol Chemistry
Abstract We present first results from a new portable Captive Aerosol Growth and Evolution (CAGE) chamber system deployed in the summer of 2013 during the Southern Oxidant and Aerosol Study (SOAS). Experiments were designed to isolate the sensitivity under ambient conditions of aerosol processes to anthropogenic factors--investigation for which the CAGE system is well suited.
The gas phase of aerosol retention/reactor volumes in each of the dual CAGE chambers are maintained in equilibrium with a continuous air flow isolated behind gas permeable ePTFE membranes. An ambient air exchange flow causes the reactor gas phase to closely follow ambient conditions. Coupled with temperature control and UV-transparency, the CAGE chambers can thus mimic the ambient photo-chemical milieu. This gas exchange stream can also be spiked (with trace gases or water vapor) or fully prescribed. Additional CAGE features include adiabatic cloud formation, equipment for generating tailored gas and aerosol samples, and analytical aerosol instrumentation including an Aerodyne HR-ToF-AMS, TDMA, SMPS and DMT-CCN.
Typical experiments contrasted the evolution of aerosol properties between a control and a perturbed chamber. The control chamber was operated to mimic ambient conditions; the perturbed chamber gas exchange flow was identical, but spiked with an anthropogenic factor such as NO$_x or ozone. In both chambers the initial aerosol was a mixture of three monodisperse aerosol with the following diameters: ~10 nm, to capture impacts on initial aerosol growth; ~100 nm, for impacts on CCN activity; and ~350 nm, to suppress nucleation. The contrast in the aged aerosol was summarized as the sensitivity of aerosol process characteristics (O:C ratio, size, hygroscopicity) to the trace gas concentration under ambient conditions. These experiments were repeated at different ambient conditions and occasionally included cloud cycles. Other primary experiments included perturbations of aerosol mass and number loading, light and dark conditions, and cloud condition perturbations.