Grantee Research Project Results

2003 Progress Report: Elemental Composition of Freshly Nucleated Particles

EPA Grant Number: R829622
Title: 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 Period Covered by this Report: January 1, 2003 through December 31, 2004
Project Amount: $390,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals

Objective:

The objective of this research project is 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 methods for chemical analysis. Because particles in this size range have had relatively little time to grow or transform in the atmosphere, their chemical compositions should more closely reflect particle formation mechanisms than larger particles that have undergone significant transformation. Chemical composition measurements will be performed with the use of a high-energy laser pulse to create a nanoplasma that quantitatively converts the particle into positively charged atomic ions.

Progress Summary:

During Year 2 of the project, a field transportable single particle mass spectrometer was evaluated that utilizes laser-induced plasma formation for elemental analysis of single particles. Particles between 30 and 100 nm in diameter were sampled through a size-selective aerodynamic focusing inlet. The range of particle sizes entering the mass spectrometer was determined by the pressure in an intermediate region of the inlet located upstream of a critical orifice. Particle size was varied by scanning the pressure.

Particle analysis was performed with laser-induced plasma (LIP). Relative to conventional laser ablation, which is used in most single particle experiments, LIP is performed with a 100x higher laser fluence. The higher laser fluence is thought to completely disintegrate the particle into atoms and then quantitatively convert the atoms to positively charged atomic ions. Studying the single particle mass spectra of several particle compositions typically found in urban air proved this concept. In most cases, the measured relative peak areas of different atomic ions matched, within experimental error, the expected peak areas based on the elemental composition of the particle. Some important exceptions were noted, for instance transition and heavy metals tended to quench the LIP, inhibiting quantitative analysis. An important advantage of LIP over conventional laser ablation is that the detection efficiency (defined as the number of particles detected divided by the number of particles irradiated with the laser) remains independent of particle size and composition. In particular, ammonium sulfate particles are detected by LIP with the same efficiency as other particle composition types. In contrast, ammonium sulfate is very difficult to detect with conventional laser ablation and has represented an important limitation of the technique in previous field studies.

Future Activities:

We will explore the ability of the instrument to characterize particles smaller than 30 nm in diameter.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

Supplemental Keywords:

nanoparticles, nucleation, ambient air, particulates, analytical, measurement methods, air, sustainable industry/business, analytical chemistry, biochemistry, chemistry, chemistry and materials science, civil/environmental engineering, engineering, physics, environmental chemistry, new/innovative technologies, sustainable environment, technology for a sustainable environment, particulate matter, aerosol composition, aerosol particles, air sampling, airborne aerosols, airborne nanoparticles, airborne particulate matter, chemical characteristics, chemical composition, chemical speciation sampling, environmental sustainability, environmentally applicable nanoparticles, mass spectrometry, membrane technology, membranes, nanotechnology, nucleated particles, sustainability., Sustainable Industry/Business, RFA, Air, Scientific Discipline, Technology for Sustainable Environment, Civil/Environmental Engineering, particulate matter, Sustainable Environment, Environmental Chemistry, Engineering, Chemistry, & Physics, Analytical Chemistry, Chemistry and Materials Science, New/Innovative technologies, Environmental Engineering, aerosol particles, sustainability, mass spectrometry, membrane technology, membranes, air sampling, airborne aerosols, chemical characteristics, nanoparticles, aersol particles, aerosol composition, airborne particulate matter, environmental sustainability, innovative technologies, chemical composition, environmentally applicable nanoparticles, nanotechnology, PM, waste reduction, chemical speciation sampling, airborne nanoparticles

Relevant Websites:

http://www.udel.edu/chem/johnston Exit

Progress and Final Reports:

Original Abstract

The 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.