Jean Muhlbaier Dasch

Atmospheric concentrations and the deposition velocity to snow of nitric acid, sulfur dioxide and various particulate species

Abstract A study of deposition velocities to snow was conducted during the 1982–1983 and 1983–1984 winters at the University of Michigan Biological Station in northern Michigan. Weekly measurements were made of dry deposition rates to snow and the atmospheric concentrations of the depositing species. SO 2 , with an average concentration of 2.2 ppb, was the dominant atmospheric sulfur containing species. NO 2 , with an average concentration of 1.8 ppb, was the dominant atmospheric nitrogenous species. NO − 3 deposition was due primarily to HNO 3 , which averaged 0.2 ppb. The HNO 3 deposition velocity averaged 1.4cm s −1 . The SO 2 deposition velocity varied with temperature, averaging 0.15 cm s −1 for samples with appreciable exposure time above − 3°C, and 0.06 cm s −1 for samples which remained below an ambient temperature of −3°C. Deposition velocities of Ca 2+ , Mg 2+ , Na + , K + and NH + 4 were 2.1, 1.5, 0.44, 0.51 and 0.10cm s −1 , respectively. The mass median diameters of these species were 4.4, 2.7, 1.8, 0.9 and 0.46 μm, respectively.

Nitrous Oxide Emissions from Vehicles

Nitrous oxide is one of the trace gases that contribute to greenhouse warming as well as stratospheric ozone depletion. The role of vehicular emissions in the global N2O budget is currently in doub...

Retention and release of chemical species by a Northern Michigan snowpack

Snowcore and water samples were collected during the 1981 to 82 winter at two independent sites in Northern Michigan; the Little Pigeon River and McNearney Lake. Acidic and basic species were determined in all samples. Examination of the concentration vs depth profiles of snow cores showed that all species were stable in the snowpack until the spring thaw period. During the thaw, 50 to 70% of the stored acids were released during the first 20% of the snowmelt. However, rainfall during the melt period contributed as much acidity to the environment as the snowmelt. Study of runoff showed that only 30% of the nitrate originally present in the snowpack appeared in the Little Pigeon River. Therefore, H2SO4 dominated the runoff acidity at the Little Pigeon River. Both nitrate and sulfate were responsible for the slight acidification of McNearney Lake during the snowmelt period.

Comparison of annular denuders and filter packs for atmospheric sampling

Filter packs have commonly been used to sample atmospheric gases and particles. However, reactions between the gases and particles can occur, particularly during summer sampling. Recently, annular denuder systems (ADS) have been developed, consisting of denuder tubes that strip the reactive gases from the air, thus leaving the particles to be collected on the ADS filters. We compared the ADS to filter packs in the winter, when the filter packs are most reliable. The species sampled included SO2, HNO3, HCl and particulate NO3−, SO42−, Na+ and Cl−. HNO2 was also sampled with the ADS. Filter packs are far less expensive than ADS and simpler to use in the field. The usual filter pack problem, dissociation of particulate NO3− to gaseous HNO3, was not apparent during winter sampling. However, the open-faced filter packs are more exposed to the elements than the ADS, thus leading to high and variable blank levels—particularly for NaCl where blank levels averaged 40% of measured concentrations. In addition, up to 50% of the SO2 was collected on the backup collector, indicating occasional poor collection efficiency. In contrast, the ADS had low blanks and high collection efficiencies with less than 3% of the SO2 on the backup collector. Measurements between filter packs and the ADS agreed within 10% for particles and hydrochloric acid. However, due to losses of HNO3 in the filter pack and small losses of particles in the denuder sections, HNO3 concentrations appear greater with the ADS than with filter packs. To the extent that the particle loss in the ADS is due to bounce-off from the impactor frit, it can be corrected in future studies. Sulfur dioxide is also 14% greater with the ADS than with the filter pack and reasons for the difference are considered.

Wintertime concentrations and sinks of atmospheric particulate carbon at a rural location in Northern Michigan

Abstract Particulate elemental carbon, organic carbon, and SO 2− 4 wintertime atmospheric concentrations were determined at a rural site in northern Michigan during two winters. Examination of the concentrations, based on both surface-wind direction and backward-trajectory analysis, indicated that concentrations were significantly influenced by the long-range transport of pollutants. Measurements of the wet- and drydeposition rates of elemental carbon showed that it is removed primarily by wet deposition at this site. The dry deposition velocity of elemental carbon to a snow surface averaged −1 during most of the study, but was considerably higher for one period during which it appeared to be influenced by large particles from local sources. A comparison of the scavenging ratios of SO 2− 4 and elemental carbon shows that snow removes SO 2− 4 at least twice as efficiently as elemental carbon. This difference implies that the atmospheric residence time of elemental carbon in the winter will be considerably longer than that of SO 2− 4 , if precipitation occurs. In the absence of precipitation, the estimated residence time of elemental carbon is at least 6 days. These results suggest that elemental carbon can be transported long distances and, thus, may degrade visibility and have other effects over wide regions.

Physical and Chemical Characterization of Airborne Particles from Welding Operations in Automotive Plants

Airborne particles were characterized from six welding operations in three automotive plants, including resistance spot welding, metal inert gas (MIG) welding and tungsten inert gas (TIG) welding of aluminum and resistance spot welding, MIG welding and weld-through sealer of galvanized steel. Particle levels were measured throughout the process area to select a sampling location, followed by intensive particle sampling over one working shift. Temporal trends were measured, and particles were collected on filters to characterize their size and chemistry. In all cases, the particles fell into a bimodal size distribution with very large particles >20 μm in diameter, possibly emitted as spatter or metal expulsions, and very small particles about 1 μm in diameter, possibly formed from condensation of vaporized metal. The mass median aerodynamic diameter was about 1 μm, with only about 7% of the particle mass present as ultrafine particles <100 nm. About half the mass of aluminum welding particles could be accounted for by chemical analysis, with the remainder possibly present as oxygen. Predominant species were organic carbon, elemental carbon, iron, and aluminum. More than 80% of the particle mass could be accounted for from steel welding, primarily present as iron, organic carbon, zinc, and copper. Particle concentrations and elemental concentrations were compared with allowable concentrations as recommended by the Occupational Safety and Health Administration and the American Conference of Governmental Industrial Hygienists. In all cases, workplace levels were at least 11 times lower than recommended levels.

Measurement of dry deposition to surfaces in deciduous and pine canopies

The importance of dry deposition was assessed at perimeter and interior locations in two vegetative canopies. Dry deposition was measured directly by washing particles from leaves. Ambient particles and gases were also collected at both locations within the canopies. Ambient concentrations on the canopy interior were decreased relative to perimeter concentrations due to dry deposition scavenging by the canopy. The least scavenging was found for SO(4)(2-) and NH(4)(+) and the highest scavenging was found for HNO(3). Dry deposition of all species was higher to perimeter vegetative and surrogate surfaces than to interior surfaces, due both to the lower concentrations and the lower wind speeds in the sheltered interior. Deposition velocities compared well with other experimental and theoretical values.

Northern Michigan snowpack—a study of acid stability and release

Abstract Weekly samples of wet deposition, dry deposition, and the snowpack were collected during the 1981–1982 winter at the University of Michigan Biological Station which is located near Pellston, Michigan. All the major acidic and basic species were determined. Comparison of the cumulative wet deposition acid loading to the snowpack loading as well as an examination of concentration vs depth profiles showed that all species were stable in the snowpack until the spring thaw period. During the spring thaw, approximately 50% of the acids were contained in the first 20 % of the snowmelt. Rainfall during the thaw period deposited as much nitrate and acid and more than double the amount of sulfate as was released from the snowpack. It was also concluded that dry deposition to snow at this location was not significant.

Assessing Potential Nanoparticle Release During Nanocomposite Shredding Using Direct-Reading Instruments

This study was conducted to determine if engineered nanoparticles are released into the air when nanocomposite parts are shredded for recycling. Test plaques made from polypropylene resin reinforced with either montmorillonite nanoclay or talc and from the same resin with no reinforcing material were shredded by a granulator inside a test apparatus. As the plaques were shredded, an ultrafine condensation particle counter; a diffusion charger; a photometer; an electrical mobility analyzer; and an optical particle counter measured number, lung-deposited surface area, and mass concentrations and size distributions by number in real-time. Overall, the particle levels produced were both stable and lower than found in some occupational environments. Although the lowest particle concentrations were observed when the talc-filled plaques were shredded, fewer nanoparticles were generated from the nanocomposite plaques than when the plain resin plaques were shredded. For example, the average particle number concentrations measured using the ultrafine condensation particle counter were 1300 particles/cm3 for the talc-reinforced resin, 4280 particles/cm3 for the nanoclay-reinforced resin, and 12,600 particles/cm3 for the plain resin. Similarly, the average alveolar-deposited particle surface area concentrations measured using the diffusion charger were 4.0 μm2/cm3 for the talc-reinforced resin, 8.5 μm2/cm3 for the nanoclay-reinforced resin, and 26 μm2/cm3 for the plain resin. For all three materials, count median diameters were near 10 nm during tests, which is smaller than should be found from the reinforcing materials. These findings suggest that recycling of nanoclay-reinforced plastics does not have a strong potential to generate more airborne nanoparticles than recycling of conventional plastics.

Characterization of Fine Particles from Machining in Automotive Plants

Sampling of the full range of particle sizes was carried out on 16 processes in six different General Motors plants over a period of 2.5 years. This article deals with particle characterization from five of the processes that relate to machining, specifically, wet machining with water-based fluids from old and new technology processes, grinding with straight oils from old and new technology processes, and dry machining. The concentrations measured by different instruments were in reasonable agreement, although the light-scattering instrument generally produced higher values than filters. Of the processes studied, the old technology grinding using straight oils generated the highest particle concentrations. The new technology controls (enclosed, vented machines) were highly effective but more so for large particles than small particles. The particle size distribution was shifted to smaller particles with enclosed processes. Dry machining generated the largest particles of all processes studied.