Development of a Dual-Sided, Temperature-Controlled, Continuous-Flow Environmental Chamber
Principal Investigators: John Shilling
Participants: Naruki Hiranuma and Chen Song
Collaborators: Lynn Russell and Shang Liu of the University of California, San Diego; Mikhail Pekour; and Dan Cziczo.
The project PI, Dr. John Shilling, inside the temperature controlled continuous-flow chamber. One of the individual two reaction chambers is shown to the right. The purple glow is generated by the UV lights, which simulate the sun. Enlarge Image
Measurements show that organic aerosol particles comprise 20 to 90 percent of the total aerosol mass. A significant portion of this organic mass (63 to 95 percent) is secondary organic aerosol (SOA), which forms in the atmosphere from oxidation of gas-phase hydrocarbons. However, models have difficulty in reproducing the SOA levels observed in the atmosphere. Accurate reproduction of aerosol concentrations has important consequences for reducing the uncertainties associated with the effect of aerosol on global climate change. Therefore, insights into SOA formation and transformations, radiative properties, and the ability of SOA particles to form liquid water and ice clouds will directly improve predictions of global climate change.
Due to limitations with the traditional experimental design, most laboratory SOA studies were conducted using high concentrations of reactants that are not representative of the real atmosphere. It is becoming clear that data collected under these conditions cannot be accurately extrapolated to atmospheric conditions and are therefore of limited use to modelers. To overcome these limitations, the PI of this project helped to develop the continuous-flow environmental chamber in which reactants are continuously injected and products are continuously generated and withdrawn from the chamber. In this configuration, semi-volatile molecules in the gas phase come to equilibrium with the chamber walls and the aerosol particles, thereby minimizing the irreversible loss of gas molecules. As a result, experiments can be conducted under atmospheric conditions and extrapolations are unnecessary.
The data derived from these chamber experiments will be used for model validation and directly incorporated into climate models developed by scientists at PNNL. In doing so, this project directly addresses one of the atmospheric-science-related high-priority questions targeted by the DOE Atmospheric System Research program: What are the climatically relevant chemical and physical properties of aerosols that control their effects on the atmosphere's radiation balance, and how can they be best represented in climate models?
One early outcome of this project is the development of the continuous-flow chamber capability at PNNL in the Atmospheric Measurements Laboratory. This new capability is now in place and being used to conduct laboratory-based research targeted at reducing the uncertainty associated with representing the SOA formation and processing in models. More information on the science questions addressed using the chamber is found below.