1999 Progress Report: Development of a Novel Condensation Nuclei Counter and Application to Ultrafine Particle FormationEPA Grant Number: R826654
Title: Development of a Novel Condensation Nuclei Counter and Application to Ultrafine Particle Formation
Investigators: Hopke, Philip K. , Mavliev, Rashid , Wang, Hwa-Chi
Current Investigators: Hopke, Philip K. , Lee, Doh-Won , Mavliev, Rashid , Smoridin, Vladimir , Wang, Hwa-Chi
Institution: Clarkson College , Illinois Institute of Technology
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $393,657
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Sustainability , Land and Waste Management , Air , Engineering and Environmental Chemistry
Ultrafine particles play an important role in atmospheric processes such as cloud formation and thus, in indirect effects on the albedo, the radiation balance, and ozone depletion. The health effects of small particles also has become a concern in recent years. Although several formation mechanisms for small particles are discussed in the literature, complete theoretical models are not available. One reason is that the atmosphere is a very complicated multiphase and multicomponent system with strong cross-influences so a complete, detailed description of this system is practically impossible. Any simplified description can only be proposed based on solid experimental data. Thus, it is important to examine experimentally the formation of ultrafine particles in the atmosphere. Limited experimental techniques are available to investigate the particle formation process. Ideal experiments would include the measurements of all relevant gas phase (trace gases, precursors, and reactive gases) and aerosol phase (the number concentration, size distribution, and chemical composition) parameters as well as the rate of gas-to-particle conversion, temperature, pressure, radiation fields, etc. An improved condensation nuclei counter is being developed to measure the nucleation of model compounds onto ions and charged particles of various kinds to examine the relationship between molecular properties of the working fluid and the particles. From these experimental results, we will develop models correlating the chemical properties of the fluid, particles, and ions with their nucleation activities.
Initial experiments have been conducted using the original turbulent mixing condensation nuclei counter (CNC) system. Supersaturation was controlled by means of changing the dibutylphthalate (DBP) vapor pressure in nozzle flow by saturating only a predetermined part of the flow while the total flow and temperature remain constant. This approach allows changing the initial DBP vapor pressure while keeping the flow structure and temperature field unchanged. The DBP concentration in the outlet of the vapor generator was measured experimentally for different ratios of saturated and bypass flows and found to be close to estimated values. Experimental results for transitions from heterogeneous nucleation to homogeneous nucleation are presented for NaCl and WOx particles at various DBP vapor pressures. With increasing DBP vapor pressure, the concentration of enlarged particles increases until reaching a plateau. At higher initial values of DBP pressure, homogeneous nucleation prevails and the number concentration of particles follows a curve typical for homogeneous nucleation recorded in the absence of nuclei. Nuclei with different mobility diameters were activated at different values of vapor pressure. Significant differences in the slopes of particle activation curves for NaCl and WOx particles exist. The reasons for such differences are a subject for the continuing research of this project, and studies continue at this time. These results will be submitted for publication in Aerosol Science and Technology.
A new turbulent mixing CNC has been designed and currently is being fabricated in Clarkson University's Research Machine Shop. The work progressed somewhat slower than initially anticipated, and was expected to be completed by the middle of November. We also have ordered the optical counters for the two units.
Once fabrication of the new CNCs is complete, the units will be sent to the Illinois Institute of Technology, where they will be assembled and initial tests of their performance will be conducted. Side-by-side tests of the two units will be conducted to ensure that they are working in a comparable manner. At that point, we will begin the detailed set of measurements involving the various types of particles as well as the various fluids. The fluids include dibutylphthalate, octadecane, 1-octadecanol, and n-octadecanolic acid, while the particle substrates are NaCl, Ag, H2SO4, and black carbon. All four working fluids have similar molecular weights and vapor pressure behavior to provide a test of the role of the functional groups in each molecule on the critical supersaturation and growth rates. The NaCl and Ag work will be conducted primarily at the Illinois Institute of Technology, and the H2SO4 and carbon particle work will be done at Clarkson University. Some replicate studies will be performed at each location to ensure reproducibility.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 20 publications||8 publications in selected types||All 8 journal articles|
||Mavliev R, Hopke PK, Wang H-C, Lee D-W. A transition from heterogeneous to homogeneous nucleation in the turbulent mixing CNC. Aerosol Science and Technology 2001,35(1):586-595.||