Grantee Research Project Results
Final Report: Elemental Composition of Freshly Nucleated Particles
EPA Grant Number: R829622Title: Elemental Composition of Freshly Nucleated Particles
Investigators: Johnston, Murray V.
Institution: University of Delaware
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2002 through December 31, 2004 (Extended to March 31, 2006)
Project Amount: $390,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Nanotechnology
Objective:
The objective of this research project was to develop a method for real-time sampling and analysis of individual airborne nanoparticles between 5 and 100 nm in diameter. The size range covered by this method is much smaller than existing single particle detection methods for chemical analysis. Particles in this size range are close to their origin, therefore chemical composition measurements of these materials should provide greater insight into particle formation mechanisms. Chemical composition was obtained through the use of a high energy laser pulse to create a nano-plasma that quantitatively converts the particles into positively charged atomic ions.
Summary/Accomplishments (Outputs/Outcomes):
During Year 3 of this project, a nano-aerosol mass spectrometer (NAMS) was developed for elemental analysis of single particles below 10 nm in diameter. This instrument builds on lessons learned from previous years’ work. Particle analysis is accomplished through a combination of electrodynamic focusing and trapping. Initially, the aerosol is brought to an equilibrium charge distribution by passing it through a polonium aerosol neutralizer. Particles then enter the mass spectrometer through a modified aerodynamic inlet. After exiting the critical orifice, charged particles in the distribution are focused through a quadrupole ion lens and trapped in a three-dimensional quadrupole ion trap. Trapped particles are ablated with a tightly focused (75 mm f.l.) high power laser beam (532 nm, 170 mJ). When a particle is in the focused laser beam, a plasma is formed that vaporizes the particle and converts its contents into multiply charged positive ions. The radiofrequency potentials of the ion lens and trap are 136 kHz; 1340 V p-p and 125 kHz; 2200 V p-p, respectively, measured with a Tectronics P6105 probe. Static lens potentials and buffer gas (argon) pressure in the system are adjusted to achieve the maximum particle hit rate. Using these parameters to analyze sucrose nanoparticles that are size-selected with a nano scanning mobility particle sizer, it was found that the median particle diameter analyzed was 9.5 nm with σg = 1.1.
The instrument has been used to analyze nanoparticle standards composed of sucrose, sodium chloride, ammonium sulfate, and sodium nitrate. Consistent with previous years’ work on larger particles, the relative signal intensities of ions produced by laser atomization/ionization of the trapped nanoparticles give semiquantitative measurements of their elemental compositions.
In the final year of the project, the nano-aerosol mass spectrometer was used to determine the elemental composition of nanoparticles produced in the early stage of secondary organic aerosol formation. These particles were produced by mixing gaseous organic compounds with ozone in a flow tube reactor. Upgrades to the electrodynamic components were performed to increase the efficiency of particle detection so that ambient particles could be analyzed.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
nanoparticles, nucleation, ambient air, particulates, analytical, measurement methods, particulate matter, aerosol composition, aerosol particles, aerosol particles, air sampling, airborne aerosols, airborne nanoparticles, airborne particulate matter, chemical characteristics, chemical composition, chemical speciation sampling, environmental sustainability, environmentally applicable nanoparticles, innovative technologies, mass spectrometry, membrane technology, membranes, nanoparticles, nanotechnology, nucleated particles,, RFA, Scientific Discipline, Air, Sustainable Industry/Business, particulate matter, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Analytical Chemistry, Civil/Environmental Engineering, New/Innovative technologies, Chemistry and Materials Science, Engineering, Chemistry, & Physics, Environmental Engineering, aerosol particles, mass spectrometry, waste reduction, chemical characteristics, membranes, airborne particulate matter, nanotechnology, environmental sustainability, chemical composition, air sampling, aerosol composition, airborne aerosols, environmentally applicable nanoparticles, sustainability, nanoparticles, PM, aersol particles, nucleated particles, innovative technologies, membrane technology, chemical speciation samplingRelevant Websites:
http://www.udel.edu/chem/johnston Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.