Michael J. Pilat

Influence of the Atmospheric Aerosol on Albedo

Abstract The possible climatic effects of the secular increase of aerosols from mans activities have been coupled with the microphysics of the aerosol properties. The magnitude of the critical aerosol absorption coefficient to backscatter coefficient, (babs/ bbs)critical, was estimated for a model atmosphere corresponding to cooling or heating of the earth with increasing aerosol concentration. The babs/bbs ratio was calculated with Mie theory assuming a Junge particle size distribution and spherical particles as a function of the imaginary part of the particle refractive index (particle light absorption) and the size distribution slope. Comparing the babs/bbs ratio calculated from Mie theory to the critical babs/ bbs, cooling might ensue if the imaginary part is less than 10−3 while heating may result if it is greater than 0.1.

Size distribution of atmospheric giant particles.

Abstract The size distribution of atmospheric giant particles in the range 5–100 μm radius was measured at three locations in Washington State using a rotary inertial impactor. The size distribution was continuous at the different locations. A significant change in the slope of the dN dlog r vs. r plot of the size distribution generally occurred between 30 and 40 μm radius. The slope B ( dN dlog r = Ar −B ) in the 5–25 μm radius range averaged 2.3 while in the 40 to 100 μm radius range B averaged 6.7. A complete atmospheric aerosol size distribution for the 0.01–100 μm radius range was obtained by combining thermal precipitator (0.01–1 μm) and inertial impaction (5–100 μm) data. It followed from the calculation of the atmospheric aerosol mass distribution (assuming spherical particles of unit density) that approximately 20 per cent of the total mass was in particles of less than 1 μm radius, 35 per cent in the 1–10μm range, 45 per cent in the 10–50 μm range, and less than 1 per cent in the greater than 50 μm radius range.

Plume opacity and particulate mass concentration

Abstract A general theoretical relationship between plume opacity and the properties of particulate air pollutants has been developed. These results are in agreement with previously reported theoretical equations for specific emissions and with the known measurements of plume opacity and particle properties. A parameter K, defined as the specific particulate volume/light extinction coefficient ratio (cm3m−3m), was used to relate the plume opacity to the particle properties. Graphs of Kvs. the particle geometric mass mean radius at geometric standard deviations of 1,1.5, 2, 3,4 and 5 are presented for particles of refractive index 1.33 (water) and 1.95−0.661 (carbon). An example is included illustrating the use of the theoretical results to calculate the maximum allowable particle concentration which will meet a given Ringelmann number.

Calculation of Smoke Plume Opacity from Particulate Air Pollutant Properties

Calculation of smoke plume opacity from the properties of the particulate emission is facilitated with the use of a parameter K (specific particulate volume cm3/m3/extinction coefficient m−1) computed from theory. Graphs of K vs. the geometric mass mean particle radius at geometric standard deviations from 1 (monodisperse) to 10 are presented for particle refractive indices of 1.96–0.66i (carbon), 2.80–0.02i, 1.33 (water) and 1.50 at a wavelength of light of 550 nm. Experimental data of K for various sources are reported. Application to the estimation of the Ringelmann number is discussed and illustrated with an example.

Calculated particle collection efficiencies of single droplets including inertial impaction, brownian diffusion, diffusiophoresis and thermophoresis

Abstract Particle collection efficiencies of a single 100 μm dia. water droplet were calculated with a Runge-Kutta numerical solution for the particle equation of motion. The bulk gas properties were held constant at 65°C and 100 per cent r.h. whereas the water droplet temperature ranged from 10°C (water vapor condensing on the droplet) to 82°C (water evaporating from droplet). Potential flow was assumed for the gas flow profile around the droplet moving at its settling velocity of 30.0 cm s−1. The results show that over the 0.01–10μm particle dia. range, the calculated particle collection efficiency is significantly increased with colder water temperatures and decreased with warmer water temperatures. The calculated results for the case with both the water and gas temperature at 65°C (only inertial impaction and Brownian diffusion mechanisms) compares reasonably with previous reports.

Collection of aerosol particles by electrostatic droplet spray scrubbers

Theoretical calculations and experimental measurements show that the collection of small aerosol particles (0.05 to 5 micron diameter range) by water droplets in spray scrubbers can be substantially increased by electrostatically charging the droplets and particles to opposite polarity. Measurements with a 140 acfm two chamber spray scrubber (7 seconds gas residence time) showed an increase in the overall particle collection efficiency from 68.8% tit uncharged conditions to 93.6% at charged conditions, with a dioctyl phthalate aerosol (1.05 μm particle mass mean diameter and 2.59 geometric standard deviation). The collection efficiency for 0.3 μm particles increased from 35 to 87% when charged. During 1973–1974 a 1000 acfm pilot plant electrostatic scrubber was constructed inside a 40 ft trailer for evaluation on controlling particu-late emissions from pulp mill operations (funded by Northwest Pulp and Paper Association). Field tests performed on the particle emissions exhausting from SO2 absorption tower...

Effect of Diffusiophoresis and Thermophoresis on the Overall Particle Collection Efficiency of Spray Droplet Scrubbers

The overall particle collection efficiencies of spray scrubbers using monodisperse droplets of 100,500, and 1000 microns diameter were calculated for the cases of evaporating and condensing droplets. The properties of the gas at the inlet to the spray scrubber were maintained constant at 150°F, 100% relative humidity, and 1 atmosphere pressure. At the liquid entrance to the spray scrubber, the water droplet temperature was 50° F for the condensing case and 180° F for the evaporating case. The liquid to gas flow rate ratio for all the calculations was held constant at 4 gal/1000 acf. The gas velocity in the co-current spray tower was 1 ft/sec in the downwind direction. The calculation results show that for the particles in the 0.01 to 10 Mm diameter range, the overall spray scrubber particle collection efficiency is greater with the cooler 50°F water (condensing case) than with the warmer 180°F water (evaporating case). The effect of diffusiophoresis and thermophoresis is noticeable for all the water dropl...

Calculated particle collection efficiencies by single droplets considering inertial impaction, Brownian diffusion and electrostatics

Particle collection efficiencies in the size range of 0.1–20/μm dia. by a single droplet, were calculated using Runge-Kutta numerical solution techniques for the particle equation of motion. Calculations were done for two droplet diameters, 50 and 200μm with sedimentation velocities of 7.55 and 100 cm s−1 respectively. The droplets and the particle gas stream were assumed to be at 38°C. In all the calculations, the particle was assumed to be charged negative and the droplet charged positive. The collection mechanisms considered were the inertial impaction, Brownian diffusion and electrostatic forces. The electrostatic forces considered were the Coulombic force of attraction between the droplet and particle, the charged-particle image force and the charged-collector image force. From the calculations it was observed that among the electrostatic forces, the Coulombic force of attraction was the predominant force. The calculations predicted that in the 0.1–20 μm dia. particle range, the collection efficiencies were significantly increased when electrostatic forces were added. The calculations also predicted that when electrostatic forces were present, the 50 μm dia. droplet gave much higher collection efficiencies than the 200 μm dia. droplet for the particle size range considered.

Comparison between the light extinction aerosol mass concentration relationship of atmospheric and air pollutant emission aerosols

Abstract A comparison between the measured and calculated light extinction-aerosol mass concentration relationship for atmospheric and source emission aerosols is presented. A parameter K , defined as the specific particulate volume/light extinction coefficient ratio (cm 3 m −3 /m −1 ) is used in the comparison. The measured magnitudes range from 0·256 to 0·487 for averaged atmospheric K s and from 0.06 to 0.78 for individual source emission K s. Additional K data for source emissions and background atmospheric aerosols would be useful for estimating the contribution of various aerosol sources to atmospheric visibility reduction.

Effect of diffusiophoresis on particle collection by wet scrubbers

Abstract The effects of diffusiophoresis on participate collection by wet scrubbers are considered. Single droplet collection efficiencies are calculated for particle collection by the combined mechanisms of inertial impaction and diffusiophoresis. The resulting single droplet particle collection efficiencies are used to calculate overall scrubber efficiencies for three cases, positive, negative and zero diffusiophoresis. The calculations indicate that negative diffusiophoresis (droplet evaporation) can cause poor scrubber performance, especially for small particles, whereas positive diffusiophoresis (condensation) can result in greatly improved particulate collection.