Welcome to the Silva Group WebPage!

The Silva Group at Utah State University uses chemical analysis methods to analyze aerosol particles.  Both the size and chemical composition of particles are important for understanding atmospheric chemistry that goes on and the physics of the processes.  The Silva lab at USU currently has several members.  Phil Silva just finished his 4th year as an Assistant Professor of analytical chemistry at USU.  Mark Erupe is a 3rd year graduate student studying ambient and laboratory organic aerosols.   Sileola Akinsiku is a 1^st year graduate student who just joined the research group and will be looking at agricultural emissions of particles and gas-phase precursors. Derek Price is a junior who is working on ambient analysis of particles with a focus on combustion aerosols. John Elias is a student from Rice University who is working this summer as a research assistant synthesizing some organic nitrogen compounds that we suspect we are detecting in particles but aren’t available commercially. We currently have openings for undergraduate researchers for the coming academic year (2006).

Silva Group Alumni

Eric Vawdrey (2003-2006) graduated from USU this spring with a BS in Chemistry (Life Science emphasis) and is currently enrolled at the UofU Pharmacy program.

Rachel Cummings (2005-2006) graduated from USU this spring with a BS in Industrial Hygiene and is working for Kennecott.

The AMS:

Our main instrumentation is the aerosol mass spectrometer (AMS), seen at left.  The AMS was developed by Aerodyne Research, Inc .  We are currently using the AMS to analyze airborne particles in the Cache Valley, where USU is located.  The AMS obtains both size and chemical composition information on the non-refractory components within particulate matter.  For more information about our research using the AMS, follow the links below.  To find out about other research being performed throughout the world with the AMS, and details about how it works, you can see the page maintained by Professor Jose Jimenez at the University of Colorado.

We have mostly used the AMS for analysis of ambient air particles in Logan (the Cache Valley).  The Cache Valley is in danger of being classified as a non-attainment area for PM_2.5 (all particles less than 2.5 µm) by the EPA.  As of right now, we are still in compliance with federal health standards (barely).

Previous Studies involving the AMS:

January-March 2004: Cache Valley Chemistry Study (Logan, UT)

January-February 2005: Cache Valley Indoor/Outdoor Comparison Study (Logan, UT and Smithfield, UT)

March 2005: Semivolatile Organic Comparison Study (Lindon, UT)

July 2005: Fireworks Study (Ogden, UT and Cache Valley)

August/Septemeber 2005: Agricultural Emissions Study (Ames, Iowa)


Upcoming Studies involving the AMS:

San Joaquin Valley Agricultural Emissions Study (August-October 2006)


We have several other projects going on in our laboratory and instruments that we use for analysis of particles.


    To the left is our Cahn microbalance, used to weigh filters from particle samples.  The microbalance can weight to seven significant digits past the decimal point (0.1 µg).  We use this for weighing ambient mass samples and for some laboratory experiments.

     We have several devices that use filters for collecting particles.   At the right is a Marple Impactor.  This is a cascade impactor that separates particles into different cuts based on size.  The Marple is an 8-stage impactor and is actually designed for personal exposure surveys, but we have used it for ambient sampling as well since we do not have a full sized impactor.                                                            




   As some of the most interesting chemistry we observe in Logan involves organic compounds, we are starting to use chromatography for analysis of molecular species in PM_2.5.  At left is a gas-chromatograph with both an FID and an ECD detector.  The FID is used for analysis of conventional organic compounds, while we hope to use the ECD for detecting organic-nitrates.

   At right is a conventional liquid chromatograph for analyzing some of the more oxidized organic compounds.

At left is our MALDI prep station.  We have been experimenting with using MALDI (Matrix-Assisted Laser Desorption/Ionization) to analyze particles collected on filters.  This apparatus allows us to prep 47 mm filters with a matrix of choice to perform MALDI analysis.  We think that MALDI can help analyze some of the very non-volatile organic compounds that are not easily amenable to chromatography (especially GC).

At right is a Differential Mobility Analyzer (DMA).  A DMA allows you to take an input of polydisperse (many sized) particles and select out a monodisperse (single size) particle.  It operates by charging the particles going in and than selecting a voltage on the long rod that allows only one size-to-charge ratio out the other end.  It is useful for making calibration particles.

This page was last updated:  July 7, 2006
Please send your comments and suggestions