Ion Mobility Analysis of Particulate Matter and Gas Phase PrecursorsEPA Grant Number: R832836
Title: Ion Mobility Analysis of Particulate Matter and Gas Phase Precursors
Investigators: Wexler, Anthony S.
Institution: University of California - Davis
EPA Project Officer: Chung, Serena
Project Period: March 6, 2006 through March 5, 2009 (Extended to March 5, 2011)
Project Amount: $372,168
RFA: Continuous Measurement Methods for Particulate Matter Composition (2005) RFA Text | Recipients Lists
Research Category: Particulate Matter , Air Quality and Air Toxics , Air
This proposal describes a suite of new instruments based on a novel (patent pending) 2D ion mobility spectrometer, that will enable a wide range of chemical aerosol measurements to be performed with light (a few kg), power stingy (<10w), and cheap (<$3K parts cost) instruments that will provide high frequency, quantitative concentrations of the gas and particulate semi-volatile compound concentrations.
The heart of these instruments is a 2D ion mobility spectrometer able to perform continuous gas-phase chemical analysis. The mobility cell separates ions in space, as does a DMA. The resulting spatial current distribution is recorded by a linear array of electrometers. Key to the viability of the mobility spectrometer is recent progress in CMOS active pixel sensors and multiplexed electrometer arrays. Arrays of 1000 electrometers are commercially available with sensitivities down to hundreds of electrons. Hamamatsu or another vender will provide these multiplexed electrometer arrays modified from their linear image sensors. Thus, the ion mobility cell and electrometer array are able to measure the concentration of gas phase components with 1-10 s temporal resolution. Pre-conditioning the sample enables particulate and gaseous analysis.
For PM analysis, ambient air is sampled through PM2.5 or PM10 cyclones. Sample air flow is carefully controlled to provide reliable cut point precision. The sample is then drawn through silica gel and activated carbon denuders where the gas phase components are removed. The sample is then heated to evaporate semi-volatiles. These vapors and the non-volatile particle components are drawn through a 63Ni beta source where the vapors are ionized. The sample is then drawn into an ion mobility cell where the ions are analyzed. The remaining particle components leave the ion mobility cell and are available for further composition analysis.
In summary, a 2D ion mobility spectrometer will be combined with standard PM and gaseous sampling components to develop instruments for analyzing gas phase precursors and the semi-volatile organic and inorganic composition of PM with 10 second temporal resolution – much faster than current instruments enabling analysis of pollutant transients that may be extremely detrimental to health.