David S. Ensor

Angular truncation error in the integrating nephelometer

Abstract The atmospheric light scattering extinction coefficient measured with an integrating nephelometer has a systematic error resulting from light lost at the angular extremes of the physical integration of scattered light. This error was calculated for typical atmospheric aerosols for the Ahlquist and Charlson instrument (integration range is 8° to 170°). The range of error resulting from angular truncation was from 0 to 22 per cent and depended primarily on the exponent of the Junge panicle size distribution and the large particle size cut-off. The error was essentially independent of the particle refractive index, small particle cut-off below 0.1 μm and the wavelength of light (436–600 nm). The calculated typical error of about 10 per cent agreed with previously published empirical and calculated results.

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.

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.

Blue moon: is this a property of background aerosol?

Stellar extinction measurements made at three astronomical observatories showed that on ~50% of the nights the extinction due to aerosol light scattering increased rather than decreased with increasing wavelength (anomalous extinction) for wavelengths close to 500 nm. This extinction behavior is analyzed in this paper and limits are established for the aerosol characteristics necessary for this phenomenon to exist, including geometric standard deviations, imaginary part of refractive index, mean radius, and gaseous NO(2).

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.

Visibility of Distant Mountains as a Measure of Background Aerosol Pollution

A relationship is developed between the visibility of distant mountains seen from an aircraft and a level of background aerosol pollution for a model atmosphere. It is found that the distance at which Mt. Rainier can be seen on clean-air days, which are typical of background aerosol levels, is consistent with the level of aerosol light-scattering measurements in other background situations.

The effect of particle size distribution on light transmittance measurement.

Light transmittance by clouds of small particles has long been used as a method to measure particle properties such as size or concentration. However, this application of light scattering has resulted in empirical data dependent on the specific instrument. Deviations from light extinction theory result when scattered light enters the detector, increasing the apparent transmittance. Previous studies of light extinction measurements have mainly considered error as a function of particle size with only limited analysis of polydispersed particle size distributions. The ratio of the expected extinction coefficient to the theoretical extinction coefficient is reported as a function of the log-normal size distribution parameters, geometric mass mean radius, and geometric standard deviation, for various detector acceptance angles.

Cascade Impactor for Sizing Particulates in Emission Sources

A cascade impactor has been designed, constructed, and evaluated for measuring the size distribution of particulates in stacks and ducts. The University of Washington cascade impactors have been used to measure the size distribution of particles emitted by a coal-fired power plant, a kraft pulp mill recovery furnace, a fluidized bed sewage sludge incinerator, and a plywood veneer drier. The University of Washington cascade impactor appears to most closely fulfill the requirements of a source test particle-size measuring system which includes isokinetic sampling capabilities, preventon of wall losses and water vapor condensation, structural ruggedness, and the ability to determine the aerosol size distribution with a minimum of effort and expense.

Trace element loss onto polyethylene container walls from impinger solutions from flue gas sampling

Trace element loss between collection and analysis from liquid environmental samples may be large. This paper describes losses to polyethylene container walls of As, Hg, Sb, Se, Cd and Zn, elements likely to be present in the vapor phase in flue gas from pulverized coal utility boilers. Losses were measured in four types of impinger solutions commonly used to absorb volatile elements. Adsorption losses were measured by adding radiochemical tracers to the selected impinger solutions (double distilled H/sup 2/O, and 10% solutions of H/sup 2/O/sup 2/, Na/sup 2/CO/sup 3/ and ICI) and measuring the amounts adsorbed onto their container walls over a period of up to 100 days. Arsenic, Sb, and Se showed only small losses. Zinc, Cd, and Hg were stable in some solutions and unstable in others. Freeze dried samples had no measurable losses.