Development and characterization of a mobile photoacoustic sensor for on-line soot emission monitoring in diesel exhaust gas.

Upcoming regulations for vehicle exhaust emission demand substantial reduction of particle emission in diesel exhaust. To achieve these emission levels, the car manufacturing industry is developing new combustion concepts and exhaust after-treatment techniques such as the use of catalysts and particle filters. Many of the state-of-the-art analytical instruments do not meet the required detection limits, in combination with a high temporal resolution necessary for engine optimization. This paper reports a new detection system and the first results of its application to on-line diesel exhaust soot measurements on a engine test bench (MAN diesel engine facility Nürnberg, Germany). The instrument is based on differential photoacoustic (PA) spectroscopy of black carbon aerosol. It contains two identical PA cells, one for the measurement of the aerosol particles and one which analyses the particle-free gas. Thus, a potential cross-sensitivity to gaseous absorbers in the exhaust gas can be excluded. The PA cells were characterized in a laboratory set-up, with water vapor as reference gas and artificial soot generated by a spark discharge generator. The detection limit was found to be 2 microg m(-3) BC (for diesel soot) with a sampling rate of 3 Hz. The temporal response of the system was found to be in the order of 1 s. After full characterization of the cells, the system was transferred into a mobile 19"-rack. Characterization of the mobile sensor system under real-world conditions was performed during several measurement campaigns at an engine test bench for heavy-duty diesel engines. Results for the limit of detection, the time resolution, accuracy, repeatability, and robustness of the sensor system are very promising with regards to a routine application of the system in engine development.

Screening of pentachlorophenol-contaminated wood by thermodesorption sampling and photoacoustic detection.

The still-remaining high amounts of pentachlorophenol (PCP), used as wood preservative, in buildings and in waste wood are a potential risk for humans and the environment. To ensure a fast and selective measurement of PCP, a screening tool was developed, which is not only sensitive, but, unlike conventional methods, it requires no added chemicals, is simple, cost-effective, mobile, and capable of on-site operation. The instrument combines light-induced thermodesorption sampling followed by an external cavity diode laser based photoacoustic detector. Measurements on wood samples proved that the system can determine PCP to as low as a concentration of 10 microg/cm2 within minutes without destruction of the sample. The system was calibrated with reference to the concentration of PCP impregnated on the wood surface. It is demonstrated that measurements are not influenced by moisture content of the wood samples.

Early reversal of postoperative hypoxemia.

Peridural analgesia was combined with the respiratory-stimulant effect of doxapram for intermittent hyperinflation of the lungs to reverse early postoperative (PO) hypoxemia following inhalation anesthesia for upper abdominal operations. Twenty unpremedicated men undergoing upper abdominal operations were studied for 5 hours in the recovery room. Ten of these patients received doxapram plus peridural analgesia; the other 10, doxapram plus morphine analgesia. Rectal temperature, PaO2, PaCO2, respiratory rate, exhaled minute ventilation (VE), tidal volume (VT), and blood pressure and pulse were measured. The mean increase from control for VE was 9.6 L/min and for VT, 356 ml/breath during doxapram therapy for the morphine group. Corresponding values for the peridural group were 14.4 L/min for VE and 660 ml/breath for VT. Mean PaO2 for the morphine group decreased significantly from the corresponding preoperative value (p less than 0.005). Lack of significant change between preoperative and PO values for PaO2 for the peridural group would indicate that under the conditions of this study, early PO hypoxemia can be reversed by the combination of peridural analgesia with doxapram therapy.

Spinal anesthesia: bupivacaine versus tetracaine.

The clinical effects of equal hyperbaric doses of bupivacaine HCl and tetracaine HCl were studied and compared in 99 adult men undergoing spinal anesthesia for similar surgical procedures. The spinal anesthetic agents were used in random order in various dosages. Comparisons were made of (1) amount of anesthetic agent used, (2) elapsed time for onset of analgesia, (3) elapsed time for obtaining maximum anesthesia, (4) cephalad dermatome level of anesthesia, (5) incidence of motor blockade, and (6) duration of anesthesia. Results with the 2 drugs in equal dose, volume, and specific gravity were almost identical. However, tetracaine provided a motor block in a significantly greater number of patients than did pubivacaine (100 versus 42%, rho less than 0.001) when both drugs were used at the 9.75-mg dose level.