2002 Progress Report: Ion-Induced Nucleation of Atmospheric AerosolsEPA Grant Number: R829620
Title: Ion-Induced Nucleation of Atmospheric Aerosols
Investigators: McMurry, Peter H. , Eisele, Fred
Institution: University of Minnesota
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2002 through December 31, 2004 (Extended to December 31, 2005)
Project Period Covered by this Report: January 1, 2002 through December 31, 2003
Project Amount: $400,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Nanotechnology
The objectives of this research project are to study the role of ion-induced nucleation as a mechanism for producing new nano-sized particles in the atmosphere. We hypothesize that: (1) nucleation processes in different locations are driven by different gas-phase species, and can be homogeneous and/or ion-induced depending on time and locale; and (2) ion-induced nucleation events can be due to the growth of either positive or negative ions, and different gas-phase species are responsible for bursts of intermediate and large positive and negative ions. The ultimate objective of this research project is to develop experimentally verified models for the formation of ultrafine atmospheric particles by nucleation.
We conducted atmospheric measurements during an intensive field study in Atlanta, GA (July 22-August 30, 2002). During this study we: (1) measured ion mobility spectra for mobility sizes down to 0.5 nm; and (2) measured the composition of ions during nucleation. The ion mobility spectra were measured using the new Inclined Grid Mobility Analyzer that was built for us by Professor Hannes Tammet (University of Tartu, Estonia) with separate funds. Since August, we have been analyzing data from that study and preparing for future work.
The ion composition measurements in Atlanta showed that during the nighttime, the negative ion spectrum was dominated by NO3 and its H2O and HNO3 clusters. During the daytime when H2SO4 was present, the negative ion spectrum was dominated by HSO4¯ · H2SO4. Evidence for HSO4¯ · (H2SO4)2 was observed, but at less than 10 percent of the HSO4¯ · H2SO4 peak. Measurements suggest that the concentrations of larger ions HSO4¯ (H2SO4)2 · (NH3)n · (H2O)p (n and p = 0, 1, 2) were very low. We expected that if negative ion-induced nucleation was occurring, those large ions should have been present. In the positive spectra, we found evidence for amines, which are probably too volatile to induce nucleation. If positive ion-induced nucleation was occurring, it must have been with a wide variety of different mass compounds, because no clear peaks are evident in the higher mass portion of the spectrum.
The ion mobility spectra provide clear evidence for peaks of both positive and negative small ions with sizes in the 1-nm size range. Consistent with the ion composition measurements made by mass spectrometry, these measurements provide no clear evidence for the growth of small ions, which would have occurred if ion-induced nucleation was occurring. We conclude that, in Atlanta, ion-induced nucleation was not a significant mechanism for particle production.
During the summer of 2003, we will begin to take measurements in Boulder, CO. These measurements will give us the opportunity to search for evidence of ion-induced nucleation in an environment quite different from that found in Atlanta. These measurements will include continuous measurements of size distributions down to 3 nm, as well as periodic intensive measurements, in which we will measure ion composition, ion mobility distributions, etc.
Mr. Kenjiro Iida, a doctoral student working under Principal Investigator McMurry's supervision, will continue to analyze the data acquired in Atlanta during August 2002. In addition, recent work by Mr. Okuyama and coworkers in Hiroshima, and Fernandez de la Mora and coworkers at Yale University has suggested that it is possible to detect particles smaller than 1-nm by vapor condensation. Mr. Iida is exploring the possibility of building such a detector for this project. Such measurements would enable us to simultaneously measure the charged and neutral size distributions of much smaller sizes than is currently possible. These measurements would add tremendously to our understanding of the role of ions in nucleation, and the physics and chemistry of nanoparticle formation and growth.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 26 publications||2 publications in selected types||All 2 journal articles|
||Kulmala M, Vehkamäki H, Petäjä T, dal Maso M, Lauri A, Kerminen V-M, Birmili W, McMurry PH. Formation and growth rates of ultrafine atmospheric particles: a review of observations. Journal of Aerosol Science 2004;35(2):143-176.||