L. Ronald Johnson

The quartz content and elemental composition of aerosols from selected sites of the EPA inhalable particulate network

Abstract The elemental composition and concentration of quartz in ambient aerosols collected on dichotomous filters from the EPA Inhalable Particulate Network (IPN) in 1980 have been determined by X-ray fluorescence and mass calibration methods of X-ray diffraction (XRD). Quartz concentrations were also determined by reference intensity ratio methods of XRD from high-volume (hi-vol) filters from ten U.S. cities and were compared with data obtained from the dichotomous samples. Twenty five individual sites are represented in the quartz analysis phase of the study. These analyses demonstrate that for all IPN sites, an average of only 4.9 (±2.3) weight per cent of the coarse particle mass as measured by the dichotomous samplers consists of quartz and 0.4 (±0.7) weight per cent as quartz in the fine fraction. Continental interior sites show the highest average quartz content as well as the greatest variability. Except for highly industrialized sites, the Coastal regions and Eastern interior sites reveal the lowest quartz concentrations. The quartz levels observed at Research Triangle Park, NC, Seattle, WA, and Portland, OR, are the lowest of the dichotomous data set, whereas those at Boston, MA, and Five Points, CA, represent the highest levels. The Si concentrations obtained from the quartz analyses were compared with Si measured directly by X-ray fluorescence on the same filters. The complete aerosol X-ray spectra from some samples such as Portland, OR, shows that the Si comes primarily from minerals such as feldspars, whereas the Si in the Buffalo, NY, aerosol comes primarily from quartz. The concentration of quartz combined with elemental composition and other crustal or anthropogenic constituents observed on the filters provides a means for developing unique geographical airshed signatures for use in detailed source apportionment studies.

On the use of various filter substrates for quantitative particulate analysis by X-Ray diffraction

Abstract Seven filter substrates, representing both fiber and membrane construction, have been studied for their utility in quantitative X-ray diffraction analysis. Filter material densities, indices of refraction, specific mass densities, mass absorption coefficients, and various properties relative to X-ray diffraction from the loaded filters have been determined. The degree to which these filters are suitable for quantitative X-ray diffraction is primarily dependent upon (1) interfering background scatter; and (2) the mass per unit area of the paniculate load collected. Teflon filters have proven to be superior to all others for specific mass loadings of less than 200 μg cm −2 . For mass loadings greater than 300μg cm −2 , the ‘quartz’ or glass fiber filters provide the most suitable substrate, primarily because of the better particle retention qualities and the lack of a substrate spectrum in the diffraction pattern.

An Exploratory Analysis of Crop Hail Insurance Data for Evidence of Cloud Seeding Effects in North Dakota

Abstract The basis for the cloud seeding operations of the North Dakota Cloud Modification Project (NDCMP) is first outlined. Then the multiresponse permutation procedures are applied in an analysis of crop hail insurance data for the NDCMP target area and for an upwind control area in eastern Montana. A historical analysis of the annual hail insurance loss ratios for the target area indicates lower hail-loss experience during the NDCMP operational years 1976–88. A corresponding analysis for the control area shows no indication of a difference during those years, suggesting the absence of any significant climatological variation. Analysis of a target–control scatterplot of the loss ratios also indicates that the target area experienced relatively smaller hail losses during the NDCMP period. An inference that the difference can be attributed to the NDCMP seeding operations appears to be justified, and the reduction in hail insurance loss ratios in the target area during the NDCMP years is estimated to be a...

Quantitative Analysis of Mt. St. Helens Ash by X-Ray Diffraction and X-Ray Fluorescence Spectrometry

Abstract A quantitative study by x-ray diffraction, optical polarizing microscopy, and x-ray fluorescence spectrometry of fallout and ambient ash from three Mt. St. Helens eruptions has revealed a consistent picture of the mineralogical and elemental composition. The major components observed are amorphous glass, plagioclase of about An50 composition, minor amounts of quartz and other SiO2 polymorphs, as well as ferromagnesian constituents such as hypersthene, magnetite, etc. Free SiO2 exists in all samples, but in no case (even considering large uncertainties in the cristobalite analyses) does the free SiO2 exceed 8% of the total aerosol mass. The variation in the glass/plagioclase ratio with particle size observed in four samples suggests that much of the crystalline material exists in the finer particle size fraction of the ash. Reduction of the mineralogical constituents to component oxides has made it possible to compare the diffraction results with direct elemental determination by x-ray fluorescenc...

Exploratory analysis of the distribution of condensation nuclei in the Northern Hemisphere upper troposphere and lower stratosphere during the late 1970s

Data obtained from the Global Atmospheric Sampling Program (GASP) during the late 1970s are used to evaluate the hypothesis that particulate emissions by aircraft are a significant source for the upper tropospheric/lower stratospheric fine and ultrafine aerosol. Measurements of condensation nuclei (CN) were acquired above 6 km mean sea level as part of GASP from October 1977 through June 1979, using automated packages on up to four commercial airliners simultaneously flying their normal daily routes. These routes spanned much of the midlatitude Northern Hemisphere, with the notable exceptions of the former Soviet Union and China. The GASP measurements are analyzed to determine the vertical, geographical, and seasonal distribution of upper tropospheric/lower stratospheric CN in clear air, spanning an altitude range from several kilometers above to several kilometers below the tropopause. The general lack of vertical gradients in median CN mixing ratio at altitudes in the troposphere suggests that CN in the clear troposphere are generally well mixed. CN mixing ratios decrease with distance above the tropopause, consistent with a tropospheric source for stratospheric CN. Median CN mixing ratios for selected regions were compared to the Northern Hemisphere median, by altitude and season. Regional median CN mixing ratios can differ from the hemispheric median by more than a factor of 2 but never an order of magnitude. The lack of vertical variation of CN concentrations in the troposphere is not at all consistent with the vertical variation of fuel consumed by aircraft, which peaks at altitudes near the tropopause. The observations of CN show some regional medians exceeding Northern Hemisphere medians in some seasons and not others, but the regions with the highest medians are not always those with the highest aircraft fuel consumption. We conclude that aircraft emissions are not a major component of the global clear air background CN measured during GASP.

Limits of detection and artifact formation of sulfates and nitrates collected with a triple-path denuder

Abstract Ammonium sulfate and nitrate aerosols were generated and sampled on Teflon (PTFE) filters in a triple-path denuder (TPD) at the Research Triangle Institute. Lower limits of detection and quantitative analysis of the resulting samples were completed by X-ray diffraction at the South Dakota School of Mines and Technology. Denuder coatings included oxalic acid for removal of ammonia, and NaCl for capture of nitric acid; a third path was left uncoated. Primary aerosol concentrations of 17 and 79 μg m−3 for (NH4)2SO4 (mascagnite), and 10 μg m−3 for NH4NO3 were generated by a nebulizer and introduced to the instruments PM10 sampling inlet under a Tedlar chamber. Monitoring of generated species during collection at RTI was conducted using ion chromatography. Lower limits of detection (LLD, as wt%) for the sulfate and nitrate collections on the filters varied from 0.9 to (as high as) 22 for extremely light filter loadings. Spalling of the oxalic acid coating along denuder A and contamination of the aerosol in the collection cassette resulted in an initially rapid but decaying rate of artifact reaction of the mascagnite to letovicite (NH4)3H(SO4)2 over several months of laboratory storage. No analogous reaction was observed for the NH4NO3 aerosol samples.

A Triple-Path Denuder Instrument for Ambient Particulate Sampling and Analysis

Abstract A field instrument for sampling sulfate and nitrate particulate matter in a controlled chemical environment has been constructed and field tested. The instrument contains HNO3 and NH3 denuders and an ambient air path, all connected by manifold to a PM-10 size-selective inlet. Ambient aerosols are collected on acid-washed quartz filters mounted in the front compartment of dual stainless steel cassettes. The rear cassette chamber contains backup filters which allow denuder breakthrough detection and specific gas measurements. The aerosol collection system has been designed specifically for use with x-ray diffraction analysis methods. An investigation of denuder coating reactions reveals that multistage reactions take place with ammonia absorbed by oxalic acid, and that nitromagnesite is formed by reaction of nitric acid with magnesium oxide coatings. Reference intensity constants needed for quantitative x-ray diffraction analysis of denuder reactions, filter pack reactions, and ambient atmospheric ...

Provenance Factor Analysis of Fugitive Dust Produced in Rapid City, South Dakota

A study of the fugitive dust sources in Rapid City, South Dakota, has resulted in the definition of four distinct geographic regions from which 11 different natural mineral compounds and industrial by-products have been quantified by recently developed x-ray diffraction methods. The results of a mass-balance analysis of the data reveal that limestone quarry operations, reentrained street dust, and construction are the major contributors to the fugitive dust levels in the city.

A Modified ATI Technique for Nowcasting Convective Rain Volumes over Areas

This paper explores the applicability of the area-time-integral (ATI) technique for the estimation of the growth portion only of a convective storm (while the rain volume is computed using the entire life history of the event) and for nowcasting the total rain volume of a convective system at the stage of its maximum development. For these purposes, the ATIs were computed from the digital radar data (for 1981-1982) from the North Dakota Cloud Modification Project, using the maximum echo area (ATIA) no less than 25 dBz, the maximum reflectivity, and the maximum echo height as the end of the growth portion of the convective event. Linear regression analysis demonstrated that correlations between total rain volume or the maximum rain volume versus ATIA were the strongest. The uncertainties obtained were comparable to the uncertainties which typically occur in rain volume estimates obtained from radar data employing Z-R conversion followed by space and time integration. This demonstrates that the total rain volume of a storm can be nowcasted at its maximum stage of development.

On the distribution of condensation nuclei (CN) in the upper troposphere/lower stratosphere and the nature of CN sources and sinks

Condensation nuclei (CN) concentrations in the upper troposphere/lower stratosphere were measured for 15 months in the late 1970’s during the Global Atmospheric Sampling Program. Automated instrument packages on 4 commercial transport aircraft recorded CN concentrations several times per hour during routine passenger-carrying operations above 6 KM MSL over much of the Northern Hemisphere. These data show clear evidence that CN are well-mixed in cloud-free tropospheric regions, that the dominant sources of CN are in the troposphere or at the earth’s surface, and that the cold trap at the tropopause is a region of primary CN nucleation or a region where otherwise undetectable CN are caused to grow to sizes detectable by the GASP CN instrumentation.