Impactor Measurements Research Articles

Characterization of Dusts Collected from Swine Confinement Buildings

As part of a project to evaluate health hazards for workers in swine confinement buildings, the air in 21 different buildings was sampled with 37 mm cassette filters with and without cyclone preselectors and with cascade impactors. Filter results yielded a mean total aerosol of 6.3 mg/m3, a mean respirable aerosol of 0.5 mg/m3; the geometric mean diameter was 2.9 microns. Cascade impactor measurements revealed a mean total aerosol of 7.6 mg/ m3, a respirable aerosol of 2.5 mg/ m3 and a mass median diameter of 9.6 microns. The two major constituents in these aerosols were grain particles and dried fecal matter. The grain particles were larger than fecal particles and proportionately more abundant in finishing buildings where 50 kg-100 kg animals are housed. Therefore the respirable fraction was less in finishing buildings than in farrowing and nursery buildings. Culturing of settled dusts yielded six different mold species, with the highest counts for Verticillium sp. (5 × 102 cfu/mg dry dust) grown at 37° C. Thermophilic Actinomycetes and both gram negative and gram positive bacteria were isolated. Azocasein proteinase activity was found in most dust samples analyzed. This dust had a protein content of about 23% and a mean adsorbed ammonia content of 0.4%.

Vertical distribution of aerosol strong acid and sulfate in the atmosphere

Vertical profiles are reported for sulfate, for strong acid‐to‐sulfate molar ratios, and for related species. Data were obtained in the northeastern United States by airborne filter‐pack sampling at multiple altitudes with some concurrent ground measurements and by impactor measurements on the ground and aloft, using semiquantitative FTIR spectroscopic analyses. Filter‐pack and impactor approaches were compared during one experimental period. Vertical profile data demonstrate that acid‐to‐sulfate ratios in ambient aerosols usually increase with altitude (Z) in the lower troposphere, occasionally remain constant with Z, and almost never decrease with Z. The sum of nitrate and nitric acid decreases with Z, but the fraction as nitric acid increases with Z, consistent with the aerosol acidity data. Urban effects on the acid‐to‐sulfate ratios in aerosols are demonstrated. The results strongly suggest that reequilibration of the aerosol nitric acid‐ammonia system must be occurring rapidly and that strong acids (in aerosols and gases) may be available for long‐distance transport in the lower troposphere.

PADRE: A Computerized Data Reduction System for Cascade Impactor Measurements

An interactive computer resource for analyzing, evaluating, and archiving particle size distributions as determined by cascade impactors for environmental measurement is decribed. The Particle Data Reduction (PADRE) computer program assists users in obtaining high quality size-mass distribution data for archival in the Fine Particle Emissions Information System (FPEIS). PADRE users interactively store, edit, reduce, and analyze observed impactor data from anywhere in the continential United States. Extensive data quality checks and computer- prompted, user-directed program operations assist users in obtaining meaningful information within minutes of entering impactor data. Design goals, program operation, sample sessions and plans for future system development are discussed.

Reducing Blowoff in Cascade Impactor Measurements

Fourteen fly-ash-size distributions were obtained with Meteorology Research, Inc. (MRI) cascade impactors at the outlet of a coal-fired utility boiler. To reduce errors due to particles blowing off or bouncing off larger particle impactor stages and collecting on following stages, jet velocities were kept low, sampling times were kept short, and a duplicate sixth stage was used between the usual sixth and seventh (last) stages. Significant collection of oversized particles was evident only on the last stage; this collection was highly correlated with jet velocity. Since considerable material was collected by the duplicate stage, the error in particle mass on the last stage would probably have been significantly worse without the duplicate stage.

Southern scandinavian aerosol composition and elemental size distribution characteristics dependence on air-mass history

The influence of aerosol long range transport in southern Sweden was investigated from a data base consisting of simultaneous cascade impactor measurements at three sampling stations, two coastal and one inland rural location. The study focused on S and heavy metals determined by particle induced X-ray emission (PIXE) analysis. The influence of local emissions was minimized by eliminating samples which were strongly suspected to be contaminated. These were identified through size distribution alterations in combination with the concentration levels obtained. Based on air mass back trajectories the samples were classified into either a southern, a northern or an eastern sector or into one of the buffer sectors located in between the sectors mentioned above. Sector S elemental concentrations were generally one order of magnitude higher than those of sector N, while intermediate concentrations were found in the E sector. Intercomparisons of simultaneous fine mode elemental concentration measurements classified into sectors S and N, respectively, provides a method for calculating the sector S foreign contribution of the elemental concentrations in southern Sweden. These calculations, not based on emission data, result in a foreign contribution of the order of 50–90 % (lowest for components like V and Ni and highest for Ti, Mn and Zn) to the metal concentrations. The multivariate statistical method SIMCA revealed that the sector S aerosol elemental composition was dependent on particle size in the accumulation mode. Elements such as S and V (or Ni) normally assumed to originate mainly from the same sources (fossil fuel combustion) were clearly separated and instead S clustered with K, Mn and Zn. This indicates that the transformation processes are more important for the covariation of S with other elements than the source origin. Transformation of SO 2 in hygroscopic particles rich in K., Mn and Zn (compared with less hygroscopic particles rich in V and Ni) is a possible mechanism which would explain the results found.

Lidar and Balloon-Borne Cascade Impactor Measurements of Aerosols: A Case Study

Aerosol size distributions, elemental components, complex refractive indices, extinction profiles and extinction-to-backscatter ratios have been measured and inferred from balloon-borne cascade impactor and lidar observations made during a cooperative joint experiment conducted during the period 4–10 April, 1980 in Tucson, AZ. Size distributions obtained from quartz crystal microbalance (QCM) cascade impactor measurements at different heights (1 to 1000 m) and times over a period of several days were fairly similar in form, being clearly bimodal in their mass distributions with the coarse particle mode being dominant. Electron microscope and energy dispersive X-ray analyses of particles deposited on the QCM stages over the particle radii range ∼0.5–4.0 μm revealed that the particle samples were elementally dominated by both sulfur and crustal type (Al, Ca, Mg and Si) elements. Complex refractive index estimates for a wavelength of 649 nm were obtained by comparing the lidar inferred aerosol extinction-to-...

Origins of aerosol sulfur size distributions in the Los Angeles basin

Low pressure impactor measurements show two distinct types of fine particle sulfur size distributions in Los Angeles, California. These two types of aerosol sulfur have mass median diameters of 0.54 ± 0.07μm and 0.20 ± 0.02 μm, respectively. Factors which may account for the two distribution types, including effects of relative humidity, coagulation, fogs and formation mechanisms, are discussed. Calculations show the 0.5 μm sulfur is consistent with chemical reactions in the aerosol phase, whereas the 0.2 μm sulfur results from homogeneous gas phase SO 2 oxidation. While the growth of the total aerosol volume distribution is not too sensitive to the mechanism, the chemical species distribution strongly depends on the growth law, and can be used to establish its form.

Data inversion for cascade impactors: Fitting sums of log-normal distributions

The processing of data from cascade impactors is discussed and the effects of non-ideal response characteristics on impactor measurements are shown. Since atmospheric particle size distributions may contain two or three modes, the sparse data from an impactor cannot give detailed information about the shape of individual peaks. Thus a shape must be assumed, and it is suggested that a log-normal form is appropriate. A procedure is described which fits sums of log-normal distributions to impactor data, taking account of the detailed response functions. This procedure has been tested with simulated data including random errors, where it is found to reproduce the input distributions satisfactorily, and with actual atmospheric data.

Physical characterization of diesel exhaust particles in exposure chambers

Since the deposition of particulate in the respiratory system is strongly influenced by particle size, a correct assessment of this parameter is important for any inhalation experiment studying the potential health effects of air pollutants. Measuring the distribution of particles according to their aerodynamic diameter and mechanical mobility diameter is crucial in analyzing the deposition of submicron particles in the lower respiratory system. Cascade impactor measurements of diluted diesel exhaust in 12.6 m 3 animal exposure chambers in the GMR Biomedical Science Department showed that the mass median aerodynamic diameter of the aerosol was 0.2 μm with 88% of the mass in particles smaller than 1 μm. Diffusion battery measurements showed that the mass median mechanical mobility diameter was about 0.11 μm. Transmission electron micrographs of particles deposited on chamber surfaces revealed both agglomerates and nearly spherical particles. The particles in these chambers are similar in size and shape to diesel particles described elsewhere. The flux of diesel particles to food surfaces was measured. Calculations of the expected daily dose by inhalation and by feeding showed that the “worst case” dose by feeding was only about one-tenth the dose by breathing.

Determination of the density and morphology of submicron ammonium chloride particles

A procedure using transmission electron microscopy in combination with a microphotometer is described to determine the density of individual ammonium chloride particles. The particles, formed by homogeneous nucleation from the gas phase, were very porous and showed an average density of 0.146 ± 0.013 g cm −3. Experiments in which the total exposure to the electron beam was increased indicated that the energy absorbed did not cause significant sublimation of the particles during the electron microscopy. Furthermore, cascade impactor measurements of the particle size confirmed this low density.

Cascade impactor measurements of the size distribution of the major classes of organic pollutants in atmospheric particulate matter

Airborne particulate matter from a suburban area was fractionated in a 6-stage high volume cascade impactor and analysed for about 60 organic pollutants by programmed multiple ion detection gas chromatography-mass spectrometry. The distribution, as a function of particle size, has been measured for the aliphatic hydrocarbons, carboxylic acids, polynuclcar aromatic hydrocarbons (PAH) as well as some aza-heterocyclic polyaromatics. The observed distribution patterns are very similar. Most aliphatic hydrocarbons (85–90°) are found on particles below 3μm. The carboxylic acids are found for 90–95% below 3 μm. The PAH distribution is strongly subjected to seasonal variations : 95–98% below 3 μm and 70–80% below 1μm in winter. For the PAH eight different, but closely related types of distributions were measured. In winter, the distributions shift toward the smaller particles. Indications for artefacts produced by volatilisation are advanced : the lower PAH show a flatter distribution in the smaller size range. Also, the alternating concentration levels of even and uneven n-alkenes could be due to selective losses for the even alkenes, since there is a correlation with the molar heat of vaporisation of the homolog series.

Comparison of volume and mass distributions for denver aerosols

Using data of the Denver 1971 aerosol characterization study, volume concentration distributions calculated from size distribution measurements by the Minnesota Aerosol Analyzing System (MAAS) are compared to mass concentration distributions measured by 8-stage Andersen impactors. In this study, the upper mode was confirmed by the impactor measurements. The lower mode was not confirmed, probably due to poor resolution resulting from impaction onto the glass fiber filters used as impaction surfaces. However, the total mass in the lower impactor mode was in agreement with the mass inferred from the volume of the lower MAAS mode. In the submicron range, estimates of densities of 1.6–1.8 g cm −3 are inferred for background aerosols and 1.1–1.5 g cm −3 for pollution aerosols.

On the Size Distribution of Raindrops in Hurricane Ginger

Abstract Airborne foil impactor measurements in Atlantic Hurricane Ginger (1971) show a raindrop size spectrum which is well represented by an exponential relation of the Marshall-Palmer type. No difference was observed between the spectral characteristics of the rainbands and those of the eyewall, but some dependence of the slope-rainfall rate relation on rainwater content was noted.