A Portable Device for Real-Time Measurement of the Size and Composition of Atmospheric AerosolsEPA Grant Number: R826769
Title: A Portable Device for Real-Time Measurement of the Size and Composition of Atmospheric Aerosols
Investigators: Johnston, Murray V. , Eiceman, Gary A.
Institution: University of Delaware , New Mexico State University - Main Campus
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $580,963
RFA: Air Pollution Chemistry and Physics (1998) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air , Engineering and Environmental Chemistry
Description:The goal of this research is to develop and field test a portable device for real-time size and composition measurements of atmospheric aerosols. Individual particles are sized with a commercial aerodynamic sizer and then ablated with a pulsed laser. Ions produced by the ablation process are analyzed by ion mobility spectrometry. Each particle gives a unique mobility spectrum that can be related to chemical composition. This approach has two important advantages over more familiar methods involving mass spectrometry. First, the mobility spectrometer operates at atmospheric pressure. Since high vacuum pumps are not needed, the size and electrical power requirements of the instrument are greatly reduced. Second, sizing is performed by an industry- standard aerodynamic method. Calibration of the particle size distribution is relatively straight forward, and size-dependent biases of the particle transmission efficiency are minimized. Thus, laser ablation ion mobility spectrometry has great potential as a portable, stand-alone device for correlated size and composition measurements.
Approach:This project is a blend of instrument development, fundamental investigations of ion mobility spectrometry and field testing. Instrument development will emphasize the adaptation of proven, field-worthy, commercially available technologies toward the goal of correlated size and composition measurements. Once the instrument has been built, fundamental work will be performed to establish and validate the link between mobility spectra and chemical composition of aerosol particles. Important parameters to be investigated include the roles of laser irradiance, particle size, relative humidity and matrix effects on the distribution and mobilities of ions produced by laser ablation. Field testing will be performed in tandem with ongoing investigations of ambient aerosols by mass spectrometry. The instrument developed in this work will be operated side-by-side with an aerosol mass spectrometer and conventional impactor instruments to compare performance.
Current methods for real-time correlated size and composition measurements are bulky and require substantial electrical power. In contrast, the instrument developed in this work is portable and will not be constrained to specialized measurement sites. Therefore, ambient measurements should be possible over a wide range of locations. The instrument developed in this work will be a research-grade device. In the future, a number of automated instruments could be built and operated for extended periods of time to provide essential data to correlate to epidemiological health indicators. The fundamental work, though not directly related to instrument development, is required to correctly interpret chemical composition data from the instrument.
Improvement in Risk Assessment or Management: Aerosol particles are important in a variety of air pollution processes. In particular, epidemiological studies suggest a link between particle mass (PM) concentration and human health. There is growing evidence that fine particles are toxic, possibly independent of composition. It is likely that a thorough understanding of health effects will ultimately require more information on the chemical composition of these particles in the atmosphere. Portable instruments, such as the one developed in this work, are needed so that correlated size and composition measurements can be performed at a wide range of locations, independent of specialized service facilities available only at specific sampling sites.