The measurement of diesel vehicle exhaust particulate mass is currently accomplished using filter collection methods according to the Code of Federal Regulations (CFR). Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Extensive testing of five different measurement methods has demonstrated that fast response measurements of diesel exhaust particulate mass concentrations, consistent with CFR filter measurements, are feasible using existing technology. The measurement principles of choice are the real time weighing of exhaust samples as implemented in the tapered element oscillating microbalance (TEOM) and the measurement of light scattering from exhaust particles as implemented in the DustTrak nephelometer. Each of these two instruments has distinctive strengths. The TEOM excels in the area of constant calibration, independent of vehicle. For the DustTrak, this calibration varies by vehicle. On the other hand, the DustTrak has an excellent signal-to-noise ratio, freedom from interference due to other exhaust sample properties, good time resolution, and simplicity. The strengths of the two measurement methods are complimentary, so an obvious suggestion is to integrate them. The nephelometer would obtain a fast response signal, with near real time calibration provided by the microbalance.
The measurement of elemental carbon (EC) and organic carbon (OC) mass for particles emitted by diesel vehicles is currently accomplished using particle collection on filters, followed by analysis using the thermal/optical reflectance carbon analysis method (TOR) or one of its variations. Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Testing of five different measurement methods has demonstrated that fast response measurement of diesel exhaust particulate EC and OC concentrations, consistent with TOR filter measurements, is feasible using existing technology. EC mass concentrations are best measured through determination of particulate light absorption with a photoacoustic instrument or determination of light extinction with a smoke meter. The photoacoustic instrument has the better dynamic range and sensitivity, whereas the smoke meter is a simpler instrument. Fast response OC measurements cannot be made with any single instrument tested. However, a combination of real time weighing as implemented in the tapered element oscillating microbalance with the photoacoustic instrument has been shown to be capable of determining OC concentrations with good time response. The addition of a nephelometer to the OC measurement could potentially improve time resolution, freedom from interferences, and sensitivity.
The Las Vegas Valley PM10 Study was conducted during 1995 to determine the contributions to PM10 aerosol from fugitive dust, motor vehicle exhaust, residential wood combustion, and secondary aerosol sources. Twenty-four-hr PM10 samples were collected at two neighborhood-scale sites every sixth day for 13 months. Five week-long intensive studies were conducted over a middle-scale sub-region at 29 locations that contained many construction projects emitting fugitive dust. The study found that the zone of influence around individual emitters was less than 1 km. Most of the sampling sites in residential and commercial areas yielded equivalent PM10 concentrations in the neighborhood region, even though they were more distant from each other than they were from the nearby construction sources. Based on chemical mass balance (CMB) receptor modeling, fugitive dust accounted for 80-90% of the PM10, and motor vehicle exhaust accounted for 3-9% of the PM10 in the Las Vegas Valley.
Psychoimmunology has been credited with using the mind as a way to alter immunity. The problem with this concept is that many of the current psychoimmunology techniques in use are aimed at alleviating stress effects on the immune system rather than at direct augmentation of immunity by the brain. Studies in animals provide a model that permits us to approach the difficulties associated with gaining an understanding of the CNS-immune system connection. A particular advantage of using animals over humans is that psychological and social contributions play a less prominent role for animals than for human subjects, since the animals are all inbred and reared under identical controlled conditions. If the insightful information provided by animal studies is correct, then psychotherapy for the treatment of diseases might be made more effective if some aspect of this knowledge is included in the design of the treatment. We emphasize conditioning as a regimen and an acceptable way to train the brain to remember an output pathway to raise immunity. We propose that a specific drug or perception (mild stress, represented by rotation, total body heating or handling) could substitute and kindle the same output pathway without the need for conditioning. If this view is correct, then instead of using conditioning, it may be possible to use an antigen to activate desired immune cells, and substitute a drug or an external environmental sensory stimulus (perception) to energize the output pathway to these cells. Alternatively, monitoring alterations of body temperature in response to a drug or perception might allow us to follow how effectively the brain is performing in altering immunity. Studies with animals suggest that there are alternative ways to use the mind to raise natural or acquired immunity in man.
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