Atmospheric and Aerosol Chemistry
Drs. Don Stedman and Gary Bishop are involved in furthering the application of their instrument, the Fuel Efficiency Automobile Test (FEAT) device. The FEAT is an instrument capable of remotely measuring tailpipe emissions from vehicles as they drive on the road. As such it is often referred to as a remote sensor. In 1987 with a grant from the Colorado Office of Energy Conservation the first successful FEAT was made and used to test light-duty vehicles in Colorado.
The FEAT was designed to emulate the results one would obtain using a conventional garage-type exhaust gas analyzer. An infrared and ultraviolet source are shined across a roadway onto multiple detectors which detect changes in the atmospheric concentrations of carbon dioxide (CO2), carbon monoxide (CO), unburned hydrocarbons (HC) and nitric oxide (NO) before and after the vehicle (figure to the right). A video picture of the back of the vehicle is simultaneously recorded. Because the effective plume path length and amount of plume seen depend on a number of factors the FEAT reports mass ratios of CO, HC, or NO to CO2 or gram of pollutant/kg or gallon of fuel consumed. Using these measured ratios as inputs to a standard combustion equation for gasoline many components of the vehicle operating characteristics can be determined including the instantaneous air/fuel ratio and the %CO, %HC, and %NO which would be read by a tailpipe probe.
The FEAT has been shown in double blind comparisons to be accurate to ±5% for CO and ±15% for HC. The NO channel is comparable to CO with a best case noise limit of 20 ppm, but has yet to be evaluated in a double blind experiment. The video picture allows vehicle information from DMV to be correlated with the emission measurements. The FEAT completes the entire measurement process in less than a second and is capable of measuring in excess of 2000 vehicles per hour at a busy location. It is primarily used in single lane environments but has been successfully used on two lane interstates. The car in the photo was found in 1991 by the FEAT emitting 10.35% CO, 0.361% HC (3610 ppm) and 7.69% CO2!
Dr. Amy Bauer and her group are involved in the detection and generation of large aerosol (0.5-250 µm in diameter) particles. On-going work involves the development of a direct-ablation plasma method for the monitoring of ambient air for the presence of hazardous biological aerosols. The detection method used for this instrument is spark-induced breakdown spectroscopy (SIBS), which yields nearly instantaneous information about the elemental composition of the sampled particles. This technique was developed by Dr. Bauer and co-workers during her tenure at Physical Sciences, Inc, a small business concern in Andover, MA. PSI and DU/Denver Research Institute are collaborating on this work. A photograph of the first field prototype can be seen below to the right. 
Other ongoing work in the aerosol field relates to the generation of standards for explosives monitoring instruments such as those commonly seen at airport security checkpoints. Calibration of these devices is currently hindered by the crudeness with which the standards are made, which results in materials without controlled size distributions. Because of transport constraints, large particles will generally be detected with different efficiencies than will smaller particles.
Dr. Dwight Smith’s research group has spent many years studying the chemical and physical properties of carbonaceous particles (aka soot or black carbon [BC]) produced through fossil fuel and biomass combustion. Ubiquitous in our biosphere, this material is of natural and anthropogenic origins, and has several impacts including its effects on the earth’s radiation balance, atmospheric chemistry, and human health. Most recently, Dr. Smith and his colleague Dr. Abdul Chughtai have been applying the results of their previous research on the structure and reactivity of BC particles to the deleterious health effects resulting from their inhalation. Other research has involved in vivo experiments in which the effects of controlled addition of principal components of the particulate from diesel fuel combustion are assessed. Current work is directed toward early identification of oxidative stress-related disease markers in breath. Implications of the research include the understanding of mechanisms underlying disease processes such as asthma.
June 10, 2008
