The iron lung: a device for the continuous delivery of fine particulate matter.

In aerosol research, bag-sampling techniques are commonly used for temporary storage of aerosols. They have been used for aging studies and to integrate over fluctuations in aerosol properties and concentrations. Here, we describe the design and operation of an iron lung aerosol sampler consisting of a large volume (∼277 l) drum and a conductive drum liner. This iron lung is used for the continuous delivery of fine particulate matter. Its performance for storage and sampling of fine particulate matter has been evaluated with soot from a kerosene lamp by characterizing the change of particle number and size distribution as function of time with a scanning mobility particle sizer. Changes in these properties have been shown to be smooth, demonstrating the utility of the iron lung described here.

Time-resolved characterization of diesel particulate emissions. 2. Instruments for elemental and organic carbon measurements.

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.

Time resolved characterization of diesel particulate emissions. 1. Instruments for particle mass measurements.

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.

Particulate emission rates for unpaved shoulders along a paved road.

This paper reports the first empirical estimate of particle emissions from unpaved shoulders along paved roads. Its objectives are to develop and demonstrate an emission rate measurement methodology that can be applied in different areas; identify the mechanisms that suspend dust from unpaved shoulders and the observables related to this suspension process; and quantify PM10 mass emissions in the form of an emission rate. To achieve these objectives, fast-response observations from nephelometers and a sonic anemometer were used to characterize short-lived dust plumes generated by passing vehicles. In addition, detailed soil surface measurements determined the mechanical properties of the shoulder surfaces. Large traffic-induced turbulence events that led to significant dust entrainment were almost exclusively caused by "large" vehicles such as trucks, semis, and vehicles pulling trailers, all traveling 50-65 mph. PM10 emission rates for these large, fast-traveling vehicles were determined to be 8 +/- 4 grams per vehicle kilometer traveled under dry conditions. Emissions due to smaller vehicles such as cars, vans, and sport utility vehicles were negligible for normal on-road driving. These results indicate that the majority of PM10 emissions from unpaved shoulders is caused by relatively few vehicles.

Continuous-Wave, All-Solid-State, Single-Frequency 400-mW Source at 589 nm Based on Doubly Resonant Sum-Frequency Mixing in a Monolithic Lithium Niobate Resonator.

Sum-frequency mixing of two cw single-mode Nd:YAG lasers in a doubly resonant congruent lithium niobate resonator generated two TEM(00) beams of single-frequency 589-nm radiation. The primary beam had a power of 400 mW and the secondary beam of approximately 15 mW by use of 320 mW of 1319-nm and 660 mW of 1064-nm Nd:YAG radiation incident on the lithium niobate resonator. This corresponds to an optical power conversion efficiency of more than 40%.

Sum-frequency generation of continuous-wave sodium D(2) resonance radiation.

Sum-frequency generation utilizing two cw single-mode Nd:YAG lasers and a congruent lithium niobate crystal yielded 3.4 mW of very narrow-band (10 kHz over 1 ms) tunable 589-nm cw radiation. This simple solid-state light source is well suited for high-resolution spectroscopy of the sodium D(2) line, as was demonstrated with both conventional and FM-modulated saturation spectroscopy.

Combined Raman-elastic backscatter lidar method for the measurement of backscatter ratios.

A variation of the conventional combined Raman-elastic backscatter lidar method, the 1-2-3 lidar method, is described and analyzed. This method adds a second transmitter wavelength to the conventional combined Raman-elastic backscatter lidar. This transmitter wavelength is identical to that of the Raman receiver. One can generate the transmitted beam at this wavelength by Raman shifting the laser radiation in molecular nitrogen or oxygen. Measuring a second elastic lidar signal at the Raman-shifted wavelength makes it possible to eliminate differential transmission effects that can cause systematic errors in conventional combined Raman-elastic backscatter lidar.

Folded Jamin interferometer: a stable instrument for refractive-index measurements.

A novel two-beam interferometer for the measurement of a refractive index or its induced changes is described. This interferometer consists of only two optical elements and is largely insensitive to their movement. A laboratory prototype has been built. It uses a polarized version of the folded Jamin interferometer to allow for convenient phase adjustment.

Distortion of particulate extinction profiles measured with lidar in a two-component atmosphere.

Distortions of particular extinction-coefficient profiles measured with lidar in a two-component (molecular and aerosol) scattering atmosphere are analyzed. The error of the extinction coefficient measured at range r depends on the location of the point r(b), where a boundary value is specified, and the particulate optical depth of the atmosphere between r and r(b); the particulate backscatter-to-extinction ratio; and the ratio of particulate and molecular scattering extinction. If the near-end solution is used, small measurement errors can produce a significant divergence between the actual and the retrieved extinction-coefficient profiles, even if the boundary value and the particulate backscatter-to-extinction ratio are specified accurately. This effect is exacerbated at small values of the particulate scattering coefficient and the backscatter-to-extinction ratio. When reasonable criteria are used, feasible minimum and maximum boundary values can be specified to restrict the range of lidar equation solutions from below and from above.

Two-component velocity measurements in a supersonic nitrogen jet with spatially resolved inverse Raman spectroscopy.

Using inverse Raman spectroscopy (IRS), we directly measured two perpendicular velocity components by crossing two probe laser beams symmetrically with the pump laser beam. Because of the crossing, the spatial resolution was improved by more than 1 order of magnitude compared with that obtained with previous IRS measurements. This made it possible to map out the planar velocity and temperature distributions in a supersonic N(2) jet. The measured distributions are in good agreement with theoretical calculations. Extension to the measurement of all three velocity components is discussed.

Flow velocity measurements with stimulated Rayleigh-Brillouin-gain spectroscopy.

Using stimulated Rayleigh-Brillouin-gain spectroscopy, we report velocity measurements in an atmospheric-pressure subsonic nitrogen flow with 10% uncertainty. It is shown that the accuracy of the velocity measurements increases with gas pressure, making this spectroscopic technique ideal for measuring velocity and other parameters of high-pressure (>1-atm) atomic or molecular flows.