Final 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 Amount: $400,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Nanotechnology
The objective of this research project was to carry out measurements to assess the relative importance of homogeneous and ion-induced nucleation in the atmosphere. The work involved the development of new measurement methods, their application to atmospheric observations, and the analysis of data from those observations to assess the relative roles of ion-induced and homogeneous nucleation to new particle formation. We successfully completed all of the proposed tasks.
We developed new techniques for measuring the composition of atmospheric ions and for measuring the size-dependent charge distribution of atmospheric nanoparticles. We applied these new techniques to field measurements in Atlanta, Georgia, and Boulder, Colorado. Because the measurement methods were still under development in Atlanta, our results for the Boulder research are more conclusive.
Two approaches were used to assess the contribution of ion-induced nucleation to new particle formation. First, mass spectrometric measurements at Atlanta and Boulder showed that negative ions were of the form (HSO4-(H2SO4)m). Clusters with m equal to 1 and 2 were observed, but clusters with higher m values were not observed. These observations are consistent with model predictions of Lovejoy and coworkers. As is explained by Eisele, et al. (2006), the implication of these measurements are that ion-induced nucleation of sulfuric acid at these sites was not a significant contributor to new particle formation. Second, measurements of ion mobility distributions (0.5-6 nm) and aerosol size distributions (3.5-1000 nm) were used to assess the contribution of ion-induced nucleation to new particle formation. We found that during nucleation events, charged fractions of particles in the 2.5-5 nm range were significantly below stationary-state values, which implies that homogeneous (neutral) nucleation was dominant. We developed a model to infer the contributions of positive and negative ion-induced nucleation to new particle formation and concluded that, on average, only 0.5 percent of the new particles were produced by this process. This result is consistent with conclusions drawn from measurements of ion composition.
In summary, our work shows conclusively that, during these field studies, homogeneous (neutral) nucleation and not ion-induced nucleation was responsible for most of the observed new particle formation. This does not rule out the possibility that ion-induced nucleation may contribute significantly to atmospheric new particle formation under very different atmospheric conditions, such as in areas with much lower temperatures and higher ion concentrations.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 26 publications||2 publications in selected types||All 2 journal articles|
||Eisele FL, Lovejoy ER, Kosciuch E, Moore KF, Mauldin RL, Smith JN, McMurry PH, Iida K. Negative atmospheric ions and their potential role in ion-induced nucleation. Journal of Geophysical Research-Atmospheres 2006;111(D4):Art. No. D04305.||
||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.||