Professor Murray Johnston of the University of Delaware is supported by the Analytical and Surface Chemistry Program in the Division of Chemistry and by the Atmospheric Chemistry Program in the Division of Atmospheric Sciences to develop a nanoparticle inlet for use with aerosol mass spectrometry, and to use it for characterization of airborne nanoparticles in laboratory and field studies. At present, on-line sampling of nanoparticles from ambient air into the vacuum of a mass spectrometer is inefficient, making it difficult to study nanoparticle formation and reactivity. The inlet being developed in this work will aim to transmit nanoparticles over a broad size range, especially particles smaller than 10 nm, so that their composition can be determined. This analytical methodology will be used to study the formation and growth of nanoparticles in a coastal marine environment, and to study the formation of secondary organic aerosols.
The project will provide important information on the source and fate of nanoparticles in the environment so that their impacts on human health and the environment can be assessed. The methodology is relevant to the study of human exposure to nanoparticles in the workplace and to the study of large molecules and macromolecular assemblies in biological systems. A diverse group of graduate and undergraduate students will be educated in this interdisciplinary area involving chemistry and atmospheric science. The results of field measurements will be used as case studies for environmental chemistry coursework at the University of Delaware, and the general public will be engaged at University sponsored science outreach events.
This project supported research in the general area of environmental nanotechnology. Nanoparticles are ubiquitous in the air we breathe. They impact both human health and climate. To understand these impacts, methods must be developed that are capable of measuring the chemical composition of ambient nanoparticles. This is no small task since the mass per particle is so small. For example, a 20 nm diameter particle (the target size of this research project) contains only about 10 attograms of material, which is 14 orders of magnitude less than the mass of a grain of salt. This is like comparing the mass of a single bacterium to the mass of the earth. The intellectual merit of this research was the development and application of new methodology for sampling and analyzing airborne nanoparticles. This new methodology enabled measurements of particles in ambient air and laboratory reactors. In ambient air measurements in Lewes, Delaware and Los Angeles, California, we demonstrated the ability to distinguish "natural" nanoparticles formed by the reaction of gas phase emissions from the biosphere from "anthropogenic" nanoparticles emitted from combustion sources. "Natural" particles contain sulfate, nitrate and organic matter, while "anthropogenic" nanoparticles contain mostly hydrocarbons. In laboratory experiments we studied the formation and reaction of organic matter derived from monoterpenes that are typically emitted from pine trees. Under the conditions of these experiments, this organic matter was found to consist of approximately a 50/50 mixture of individual molecules and polymeric species from the molecules. We also studied the reaction of ammonium sulfate clusters with amines, and found that amines rapidly displace ammonia on the surface of these clusters. This process may contribute to the rate at which nanoparticles grow in the atmosphere. The broader impact of this research is the development of methodology that can be used for composition measurements in many aspects of environmental and industrial nanotechnology, not just the specific applications pursued in this work. Four graduate students supported by this project have obtained their Ph.D. degrees and are now employed full-time in academic, industrial and government positions in the United States.
