A new sampling method suitable for the routine monitoring of nitric acid and particulate nitrate ... more A new sampling method suitable for the routine monitoring of nitric acid and particulate nitrate was tested at the Nitrogen Species Methods Comparison Study in Claremont, CA during September 1985. The method is based on prior observations that the internal surfaces of the Dichotomous sampler can efficiently denude nitric acid. A Dichotomous sampler was operated with both fine and coarse filter holders modified to accommodate a Teflon membmne prefilter and nylon membrane after filter. A Tenon-iined AIHL cyclone followed by Teflon and nylon filters in series sampled total fine nitrate. particulate nitrate was determined with the Dichotomous sampler and nitric acid from the cyclone-Dichotomous sampler difference. Over 16 sampling periods, the fine nitrate and nitric acid showed excellent agreement with that obtained with two conventional MgO denuder difference sampling trains. Airborne concentrations of the major ionic species were determined with the Dichotomous sampler and good ion balances were obtained. Coarse nitrate was associated with marine air, consistent with formation by the reaction of nitric acid with sea salt. The resulting hydr~hloric acid was measured by applying the cyclon~Dichotomous sampler difference method to chloride. Thus, the new sampling method is useful for the monitoring of the chemical species important for acid deposition.
The US EPA instituted a ban on most products containing asbestos in 1989; however, automotive dry... more The US EPA instituted a ban on most products containing asbestos in 1989; however, automotive dry friction materials (ADFM) including drum brake linings were subsequently exempted from the ban in 1991. However, there is insufficient knowledge concerning motor vehicle asbestos brake dust emission rates and brake friction material inventories of asbestos, a known carcinogen. Assessment of the potential health effect consequences from asbestos brake friction materials (BFM) requires the identification of the asbestos fiber type and classification of fiber size, as well as, the determination of the asbestos concentration in brake dust emissions. Based on knowledge of the California registered vehicle population and those drum brake vehicles likely to have asbestos containing BFM, a vehicle target list was used to collect used brake shoes for asbestos analysis by polarized light microscopy (PLM). PLM analysis of used asbestos BFM collected from target vehicles currently in operation, det...
The application of forensics to environmental contamination has largely concentrated upon terrest... more The application of forensics to environmental contamination has largely concentrated upon terrestrial matrices including soil, sediments, and water; however, of equal importance are forensics investigations of airborne pollutant particles of anthropogenic origin. The recognition of highly localized community exposures to local sources of toxic aerosol emissions, have increased the burden on local air districts to identify and remediate these pollution sources. Conventional methods of collecting, extracting, and analyzing bulk particulate air samples cannot distinguish the morphology, size, and chemical composition of individual particles, which are often essential to distinguish the fingerprint of specific emission sources. The ability of spectroscopy capable microscopes to characterize both the morphology and composition of single particles and fibers in the air environment, has proven to be essential to deconvolute the sources of air contaminants that pose a threat to community he...
Recent environmental forensics investigations conducted by the Environmental Health Laboratory of... more Recent environmental forensics investigations conducted by the Environmental Health Laboratory of the California Department of Public Health are presented to demonstrate the utility of advanced microscopy techniques. These investigations utilized FTIR and scanning electron microscopy (SEM), image analysis, and Raman microspectroscopy to identify contaminant source materials in environmental samples. Microscopy techniques were developed to provide information about the morphology and composition of up to hundreds of individual particles per sample, which provides the unique fingerprint necessary for source identification for even small amounts of sample. In two investigations of combustion-derived airborne particulate contaminants, a unique passive air sampler designed to double as the microscopy analysis substrate was utilized. First, the passive sampler was used in a rural community to collect ash-like material which had settled on local outdoor surfaces. SEM equipped with energy d...
A simple sulfuric acid aerosol generator which provides a reproducible aerosol of narrow size dis... more A simple sulfuric acid aerosol generator which provides a reproducible aerosol of narrow size distribution has been developed. The method is based on the injection of heated SO, vapor in N, into a stream of humidified air. Particle diameter is adjustable from approximately 0.3 to 1.5pm with a relative standard deviation of between 0.12 and 0.20. The generator is also capable of producing particles of < 0.3 pm and > 1.5 pm under special conditions. The sulfuric acid aerosol size distribution was obtained from optical particle counter data and verified using electron microscopy. The sulfuric acid concentration range of the generator is 0.3-3 mgm-' depending upon the particle size produced.
Special appreciation is expressed to Ralph Propper, California Air Resources Board (CARB) Project... more Special appreciation is expressed to Ralph Propper, California Air Resources Board (CARB) Project Officer, for his early recognition of the necessity for improved methods for assessing the emissions of asbestos fibers from on the road vehicles, and his support of their development through approval of the interagency research agreement. Both Kevin Cleary and Alberto Ayala of CARB are acknowledged for their flexible problem solving management approach, which allowed the incorporation of new technological improvements during the course of the project. Appreciation is expressed to Joe De Vita, CARB El Monte, for his guidance in focusing the research and providing statistical data on the distribution of vehicles currently in use on California roadways. Gratitude is also expressed to Drs. Jeff Wagner and Donald Scales, Environmental Health Laboratory Branch (EHLB) Research Scientists for the development and application of a new integrated methodology for the analysis of asbestos fibers by light microscopy and electron microscopy techniques. Diamon Pon, EHLB Senior Supervising Chemist, and Frank DiGenova, Sierra Research Incorporated (SRI), are gratefully acknowledged for their crucial participation in the brake emission measurements conducted on the SRI chassis dynamometer. Student assistants Ernest Liu, Daniel Hon, and Nathan Wood are acknowledged for their hard work during the different phases of the project and their creative enthusiasm in helping to attain the project objectives. This report was submitted in fulfillment of the CARB Interagency Agreement No. 01-333 by the EHLB of the California Department of Health Services under the sponsorship of the CARB. Although over the last few years domestic manufacturers have apparently eliminated asbestos as an ingredient in BFM formulations, friction material manufacturers were considering an increase in the production of asbestos-based products. In addition, the asbestos-free BFM formulations need to be thoroughly investigated to determine the presence of substitute friction modifiers, such as crystalline silica or carbon fiber, which may present as great a health hazard as asbestos. Mitigation of the current health hazard associated with airborne asbestos exposure could utilize an early brake replacement program for target vehicles likely to employ asbestos BFM.
Although a number of models have been proposed to describe the adhesion of particles to surfaces,... more Although a number of models have been proposed to describe the adhesion of particles to surfaces, most theories are restricted to the case of the removal of precollected particles from a surface. This provides an estimate only of adhesion surface energy between the particle and substrate. In the dynamic case of an impact, it is necessary to consider the adhesion surface energy and the loss of impact kinetic energy as well as the interaction between the two mechanisms. Data from laser-Doppler measurements of kinetic energy loss were used to evaluate the few available impact-adhesion models from low impact velocities, where the major influence of adhesion surface energy is expected, up to high velocities, where plastic deformation dominates the impact.
Background The inlet is a vital component of a sampler; unfortunately, this aspect of sampler des... more Background The inlet is a vital component of a sampler; unfortunately, this aspect of sampler design has not received adequate attention. Furthermore, few samplers are equipped with inlets which have been rigorously tested. The Hi-volume sampler (I) is typical of many ...
A Laser Settling Velocimeter (LSV) has been developed for the measurement of large particle aerod... more A Laser Settling Velocimeter (LSV) has been developed for the measurement of large particle aerodynamic diameters and has been applied in the range 10—20 μm. A vertical settling tube is illuminated along the axis by a 5 mW He—Ne laser beam to permit manual timing of falling particles. Measurements on DOP particles from a vibrating orifice generator agree with diameters
Incoming and rebounding particle velocities were measured to within several particle diameters of... more Incoming and rebounding particle velocities were measured to within several particle diameters of the impaction surface using laser Doppler velocimetry. Impacts occurred normal to the surface and ranged from 1 m / s , near the threshold for particle hounce, to 100 m/s, well into the plastic damage regime. Monodisperse ammonium fluorescein spheres, 2.6-6.9 p m in diameter, impacted target surfaces including polished molybdenum and silicon, cleaved mica, and a fluorocarbon polymer. The incident kinetic energy recovered on rebound depended on particle size and target composition at low velocity ( < 20 m/s), where the adhesion surface energy is important. No dependence on target composition was found at higher velocities where up to half of the impact energy was lost to plastic deformation. Plastic deformation was a significant component of energy loss even at impact velocities near critical velocity. Critical velocities for the onset of hounce decreased with a stronger power-law dependence on particle diameter than expected from classical adhesion theory or the elastic flattening model proposed by Dahneke. This is consistent with kinetic energy loss contributions from both plastic deformation and surface forces. Auxiliary experiments conducted with and without continuous discharge of the impact surface indicated the absence of a significant electrostatic contribution to particle adhesion.
A new sampling method suitable for the routine monitoring of nitric acid and particulate nitrate ... more A new sampling method suitable for the routine monitoring of nitric acid and particulate nitrate was tested at the Nitrogen Species Methods Comparison Study in Claremont, CA during September 1985. The method is based on prior observations that the internal surfaces of the Dichotomous sampler can efficiently denude nitric acid. A Dichotomous sampler was operated with both fine and coarse filter holders modified to accommodate a Teflon membmne prefilter and nylon membrane after filter. A Tenon-iined AIHL cyclone followed by Teflon and nylon filters in series sampled total fine nitrate. particulate nitrate was determined with the Dichotomous sampler and nitric acid from the cyclone-Dichotomous sampler difference. Over 16 sampling periods, the fine nitrate and nitric acid showed excellent agreement with that obtained with two conventional MgO denuder difference sampling trains. Airborne concentrations of the major ionic species were determined with the Dichotomous sampler and good ion balances were obtained. Coarse nitrate was associated with marine air, consistent with formation by the reaction of nitric acid with sea salt. The resulting hydr~hloric acid was measured by applying the cyclon~Dichotomous sampler difference method to chloride. Thus, the new sampling method is useful for the monitoring of the chemical species important for acid deposition.
The US EPA instituted a ban on most products containing asbestos in 1989; however, automotive dry... more The US EPA instituted a ban on most products containing asbestos in 1989; however, automotive dry friction materials (ADFM) including drum brake linings were subsequently exempted from the ban in 1991. However, there is insufficient knowledge concerning motor vehicle asbestos brake dust emission rates and brake friction material inventories of asbestos, a known carcinogen. Assessment of the potential health effect consequences from asbestos brake friction materials (BFM) requires the identification of the asbestos fiber type and classification of fiber size, as well as, the determination of the asbestos concentration in brake dust emissions. Based on knowledge of the California registered vehicle population and those drum brake vehicles likely to have asbestos containing BFM, a vehicle target list was used to collect used brake shoes for asbestos analysis by polarized light microscopy (PLM). PLM analysis of used asbestos BFM collected from target vehicles currently in operation, det...
The application of forensics to environmental contamination has largely concentrated upon terrest... more The application of forensics to environmental contamination has largely concentrated upon terrestrial matrices including soil, sediments, and water; however, of equal importance are forensics investigations of airborne pollutant particles of anthropogenic origin. The recognition of highly localized community exposures to local sources of toxic aerosol emissions, have increased the burden on local air districts to identify and remediate these pollution sources. Conventional methods of collecting, extracting, and analyzing bulk particulate air samples cannot distinguish the morphology, size, and chemical composition of individual particles, which are often essential to distinguish the fingerprint of specific emission sources. The ability of spectroscopy capable microscopes to characterize both the morphology and composition of single particles and fibers in the air environment, has proven to be essential to deconvolute the sources of air contaminants that pose a threat to community he...
Recent environmental forensics investigations conducted by the Environmental Health Laboratory of... more Recent environmental forensics investigations conducted by the Environmental Health Laboratory of the California Department of Public Health are presented to demonstrate the utility of advanced microscopy techniques. These investigations utilized FTIR and scanning electron microscopy (SEM), image analysis, and Raman microspectroscopy to identify contaminant source materials in environmental samples. Microscopy techniques were developed to provide information about the morphology and composition of up to hundreds of individual particles per sample, which provides the unique fingerprint necessary for source identification for even small amounts of sample. In two investigations of combustion-derived airborne particulate contaminants, a unique passive air sampler designed to double as the microscopy analysis substrate was utilized. First, the passive sampler was used in a rural community to collect ash-like material which had settled on local outdoor surfaces. SEM equipped with energy d...
A simple sulfuric acid aerosol generator which provides a reproducible aerosol of narrow size dis... more A simple sulfuric acid aerosol generator which provides a reproducible aerosol of narrow size distribution has been developed. The method is based on the injection of heated SO, vapor in N, into a stream of humidified air. Particle diameter is adjustable from approximately 0.3 to 1.5pm with a relative standard deviation of between 0.12 and 0.20. The generator is also capable of producing particles of < 0.3 pm and > 1.5 pm under special conditions. The sulfuric acid aerosol size distribution was obtained from optical particle counter data and verified using electron microscopy. The sulfuric acid concentration range of the generator is 0.3-3 mgm-' depending upon the particle size produced.
Special appreciation is expressed to Ralph Propper, California Air Resources Board (CARB) Project... more Special appreciation is expressed to Ralph Propper, California Air Resources Board (CARB) Project Officer, for his early recognition of the necessity for improved methods for assessing the emissions of asbestos fibers from on the road vehicles, and his support of their development through approval of the interagency research agreement. Both Kevin Cleary and Alberto Ayala of CARB are acknowledged for their flexible problem solving management approach, which allowed the incorporation of new technological improvements during the course of the project. Appreciation is expressed to Joe De Vita, CARB El Monte, for his guidance in focusing the research and providing statistical data on the distribution of vehicles currently in use on California roadways. Gratitude is also expressed to Drs. Jeff Wagner and Donald Scales, Environmental Health Laboratory Branch (EHLB) Research Scientists for the development and application of a new integrated methodology for the analysis of asbestos fibers by light microscopy and electron microscopy techniques. Diamon Pon, EHLB Senior Supervising Chemist, and Frank DiGenova, Sierra Research Incorporated (SRI), are gratefully acknowledged for their crucial participation in the brake emission measurements conducted on the SRI chassis dynamometer. Student assistants Ernest Liu, Daniel Hon, and Nathan Wood are acknowledged for their hard work during the different phases of the project and their creative enthusiasm in helping to attain the project objectives. This report was submitted in fulfillment of the CARB Interagency Agreement No. 01-333 by the EHLB of the California Department of Health Services under the sponsorship of the CARB. Although over the last few years domestic manufacturers have apparently eliminated asbestos as an ingredient in BFM formulations, friction material manufacturers were considering an increase in the production of asbestos-based products. In addition, the asbestos-free BFM formulations need to be thoroughly investigated to determine the presence of substitute friction modifiers, such as crystalline silica or carbon fiber, which may present as great a health hazard as asbestos. Mitigation of the current health hazard associated with airborne asbestos exposure could utilize an early brake replacement program for target vehicles likely to employ asbestos BFM.
Although a number of models have been proposed to describe the adhesion of particles to surfaces,... more Although a number of models have been proposed to describe the adhesion of particles to surfaces, most theories are restricted to the case of the removal of precollected particles from a surface. This provides an estimate only of adhesion surface energy between the particle and substrate. In the dynamic case of an impact, it is necessary to consider the adhesion surface energy and the loss of impact kinetic energy as well as the interaction between the two mechanisms. Data from laser-Doppler measurements of kinetic energy loss were used to evaluate the few available impact-adhesion models from low impact velocities, where the major influence of adhesion surface energy is expected, up to high velocities, where plastic deformation dominates the impact.
Background The inlet is a vital component of a sampler; unfortunately, this aspect of sampler des... more Background The inlet is a vital component of a sampler; unfortunately, this aspect of sampler design has not received adequate attention. Furthermore, few samplers are equipped with inlets which have been rigorously tested. The Hi-volume sampler (I) is typical of many ...
A Laser Settling Velocimeter (LSV) has been developed for the measurement of large particle aerod... more A Laser Settling Velocimeter (LSV) has been developed for the measurement of large particle aerodynamic diameters and has been applied in the range 10—20 μm. A vertical settling tube is illuminated along the axis by a 5 mW He—Ne laser beam to permit manual timing of falling particles. Measurements on DOP particles from a vibrating orifice generator agree with diameters
Incoming and rebounding particle velocities were measured to within several particle diameters of... more Incoming and rebounding particle velocities were measured to within several particle diameters of the impaction surface using laser Doppler velocimetry. Impacts occurred normal to the surface and ranged from 1 m / s , near the threshold for particle hounce, to 100 m/s, well into the plastic damage regime. Monodisperse ammonium fluorescein spheres, 2.6-6.9 p m in diameter, impacted target surfaces including polished molybdenum and silicon, cleaved mica, and a fluorocarbon polymer. The incident kinetic energy recovered on rebound depended on particle size and target composition at low velocity ( < 20 m/s), where the adhesion surface energy is important. No dependence on target composition was found at higher velocities where up to half of the impact energy was lost to plastic deformation. Plastic deformation was a significant component of energy loss even at impact velocities near critical velocity. Critical velocities for the onset of hounce decreased with a stronger power-law dependence on particle diameter than expected from classical adhesion theory or the elastic flattening model proposed by Dahneke. This is consistent with kinetic energy loss contributions from both plastic deformation and surface forces. Auxiliary experiments conducted with and without continuous discharge of the impact surface indicated the absence of a significant electrostatic contribution to particle adhesion.
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