James B. Wedding

A Wind Tunnel Study of Gaseous Pollutants in City Street Canyons

Steady state mean concentrations of tracer gas were measured in a 400:1 scale model of an idealized city with variable geometry placed within a wind tunnel at various orientations to the mean flow for a free stream velocity of 6.8 ft/sec. The tracer gas was released from two parallel line sources to simulate lanes of traffic in an effort to quantify the persistence of pollution as well as the mean values realized at street levels. An aerodynamically rough turbulent boundary layer of neutral thermal stratification was employed to simulate the atmosphere. Values of concentration measured in the model city were converted to prototype concentrations in ppm and compared to National Ambient Air Quality Standards. It was shown that single isolated structures may cause favorable mixing of pollution downwind but very high concentrations exist in the immediate leeward vicinity of the building. Two favorable geometries for city blocks tested were found to reduce pedestrian exposure to pollution both near heavy traff...

Aerosol deposition on plant leaves

An aerosol generator and wind tunnel system designed for use in aerosol deposition are described. Gross deposition on rough pubescent leaves was nearly seven times greater than on smooth, waxy leaves. Results suggest that aerosol deposition, on a per unit area basis, for single horizontal streamlining leaves is similar to that for arrays of leaves under similar flow conditions. Wind re-entrainment of PbCl2 particles was negligible while 2.54 cm of simulated rainfall was sufficient to remove 85% of recently applied aerosol.

Wind tunnel evaluation of a modified andersen impactor and an all weather sampler inlet

Abstract Modifications were made to a one-cfm (4.72 × 10 −4 m 3 / s ) Andersen impactor to permit the collection of larger particles than previously possible. An All Weather Sampler Inlet was developed for the unit which enables acquisition of unbiased aerosol samples for varying meteorological parameters. When tested with a uranine-tagged oleic acid aerosol in a wind tunnel operated at a speed of 4.6 m/s (15 ft/sec), the standard Andersen design precludes collection of more than 50 percent of particles larger than approximately 7 μm diameter whereas the corresponding particle size for the modified system is 14 μm. Wind tunnel tests with the modified unit show the performance to be relatively unaffected by wind speeds over the range of 5–15 ft/sec or by turbulence with intensities up to eight percent. The geometrical configuration precludes wind directional effects.

Physiological effects, wind reentrainment, and rainwash of lead aerosol particulate deposited on plant leaves.

Leaves of soybean (Glycine max L.) were experimentally fumigated with PbCl/sub 2/ aerosol particulates. No indication was found for either an effect of Pb on photosynthesis or for intraplant movement of topically applied Pb. Reentrainment wind speeds up to 6.7 m s/sup -1/ had no effect in removing aerosol particulate, whereas simulated rainfall removed up to 95% of the topically applied Pb. The mechanism of dissolution or suspension and subsequent runoff appeared to predominate over that of bombardment and resultant splashoff for rain water removal of PbCl/sub 2/ particulate from soybean leaves. 25 references, 2 figures, 2 tables.

A 10-.mu.m cutpoint inlet for the dichotomous sampler

Pa (9) Horzempa, L. M.; Di Toro, D. M. Water Res., in press. (10) Huang, J.-C.; Liao, C. J. Sanit. Eng. Diu., ASCE 1970,19, Ta = (A241 1057-1078. 1 + m(r, a,) It should be noted that these relationships can be easily (11) Pierce, R. H.9 Jr.; O h Y , C. E.; Felbeck, G. T.9 Jr. Geochim. corrected for the mass associated with the residual supernatannt if its volume is known by simply adding that mass to the left-hand side of eq A14. (12)

A quantitative technique for determining the impact of non-ideal Ambient sampler inlets on the collected mass

An analytical technique has been developed which provides the basis for the upcoming Federal Reference Method delineating acceptable performance specifications for Ambient Aerosol Sampler Inlets. With the anticipated promulgation of a new Air Quality Standard based upon a size specific fraction of atmospheric aerosol, criteria must be established to allow the quantification of the non-ideal nature of inlets in terms of mass collected. The capability of inlets to collected mass with ±10% of the thoracic region of the respiratory tract was assessed by examining effectiveness curves having different slopes with various D50 values. The impetus for this criterion came from ISO TC 146 which further proposed restrictions on the shape of the inlet performance curve. Results for three typical ambient mass distributions revealed that collected mass is influenced in order of decreasing performance by the particle size associated with a sampling effectiveness of 50 per cent (D50) and the ratios D16D50 (σ16) and D50D84 (σ84).

The wedding ambient aerosol sampling inlet (D50 = 10 μm) for the high-volume sampler

Abstract The Wedding Inlet has a nominal cutpoint of 10 μm at the flow rate of the High-Volume Sampler (40 cfm, 1.13 m3 min−1) and fits existing samplers. Tests were conducted in both the wind tunnel and the field essentially as specified by 40 CFR, Part 53, Subpart D delineating performance tests for “PM-10” samplers. The results of these and additional tests were: 1. (1) D50 values ranged from 9.6 to 9.9 μm over a wind speed range of 2–48 km h−1 with only σ16 changing slightly at the 48 km h−1 condition 2. (2) D50 was essentially invariant with a volumetric flowrate change of ±10% 3. (3) particles do not reach the collection substrate when the sampler is inoperative 4. (4) D50 was essentially invariant with angle of attack (tilt) of approaching wind flow of ±21° 5. (5) effectiveness at 20 μm for solid ammonium fluorescein was 3% as compared with 1% for oleic acid particles 6. (6) a consistent D0 ≤ 25 μm was observed in field tests 7. (7) the sampler duplicates the performance of the EPA “ideal Sampler” within 5%.

Mass transfer from water droplets under simulated free-fall conditions

Abstract An experimental study was conducted to measure the rates of mass transfer from droplets of water under simulated free-fall conditions. These droplets were captured on a wire and air that was conditioned at various temperatures and relative humidities was passed by the pendant droplet in a closed loop wind tunnel facility. Droplets having nominal diameters of 100, 250, and 400 μm generated using a vibrating reed aerosol generator were sized at each time step and the wind tunnel velocity adjusted to the corresponding terminal settling velocity. The droplet diameter was determined using a specially designed, long focal length microscope, with the droplet image projected on to a solid state camera with data acquired and reduced using an on-line microcomputer. The data were used to obtain an equation of the Sherwood number ( Sh ) as a function of the Reynolds ( Re ) and Schmidt ( Sc ) numbers. The resulting correlation equation, Sh = 1.755 + 0.535 (Re 1 2 Sc 1 3 ) agreed well with data from previous studies, and it is noted that the intercept value is less than that predicted by theory.

Wedding ambient aerosol sampling inlet for an intermediate flow rate (4 cfm) sampler.

rn An ambient air inlet for an intermediate flow rate sampler has been designed, fabricated, and performance tested. The device is presently designed to operate a t 4 cfm and have an aerodynamic particle size of 10 pm associated with a 50% effectiveness value (D50), which is commensurate with the anticipated changes in the National Ambient Air Quality Standards under consideration by the U.S. Environmental Protection Agency. However, the system can be easily modified to meet any DW value ultimately selected by the Administrator. It is cost effective and potentially more accurate to collect a greater amount of mass than is possible with the current dichotomous sampler in the same 24-h period. Determination of mass may then be performed on a five-place analytical balance. A suitable filter substrate can be employed such as Teflon or microquartz, which do not have an artifact problem as observed with the standard Hi-Vol glass fiber filter. The system is independent of all environmental Conditions, including windspeed and wind direction. The inlet employs a unique, omnidirectional cyclone fractionator. The nature of the cyclonic forces in conjunction with the tortuous pathway that the transmitted particles must follow to reach the exit plane of the inlet precludes the bouncing or reentrainment of particles experienced with all impaction-type devices.

Evaluation of the Sierra-Andersen 10-μm inlet for the high-volume sampler

Abstract Wind tunnel and field tests were conducted on the Sierra-Andersen Model 321-A nominal 10 μm inlet for the High-Volume Sampler. In the wind tunnel, the inlet displayed substantial sensitivity to wind velocity, particularly with respect to serious oversampling at high wind speeds. The unit displays continuing problems of solid particle bounce which were decreased in the field by coating the collecting surfaces with oil. This performance raises questions, both about the adequacy of the sampler and of the test protocol presently prescribed by EPA, which would fail to detect these problems.