James T. Kelly

Particle Deposition in Human Nasal Airway Replicas Manufactured by Different Methods. Part II: Ultrafine Particles

Information on the deposition efficiency of aerosol particles in the nasal airways is used for optimizing the delivery of therapeutic aerosols into the nose and for risk assessment of toxic airborne pollutants inhaled through the nose into the respiratory system. Nasal particle deposition is often studied using plastic replicas of nasal airways. Deposition efficiency in a nasal replica manufactured by stereolithography has not been reported to date. We determined the inertial particle deposition efficiency of two replicas of the same nasal airways manufactured by different stereolithography machines and compared results with deposition efficiencies reported for models manufactured by other techniques from the same magnetic resonance imaging scans. Deposition in the replicas was measured for particles of aerodynamic diameter between 1 and 10 μm and constant inspiratory flow rates ranging from 20–40 Ipm. Deposition efficiency of the replicas increased from nearly 0–100% with increasing particle inertia. For a range of particle inertias, particle deposition in the replica made with higher resolution stereolithography machine was slightly less than in the replica made with a lower resolution stereolithography process. These data showed lower deposition efficiency when compared with other deposition studies in nasal replicas based on the same magnetic resonance imaging data. The differences in deposition efficiency can be attributed in part to differences in methods used to manufacture the replicas. There was little or no difference in deposition due to cutting tool size, some difference due to the use of assembly plates, and some difference due to surface roughness. These associations suggest that inertial nasal particle deposition is significantly influenced by small differences in nasal airways.

Fine-scale simulation of ammonium and nitrate over the South Coast Air Basin and San Joaquin Valley of California during CalNex-2010

National ambient air quality standards (NAAQS) have been set for PM_2.5 due to its association with adverse health effects. PM_2.5 design values in the South Coast Air Basin (SoCAB) and San Joaquin Valley of California exceed NAAQS levels, and NH^(+)_(4) and NO^(-)_(3) make up the largest fraction of total PM2.5 mass on polluted days. Here we evaluate fine-scale simulations of PM_(2.5) NH^(+)_(4) and NO^(-)_(3) with the Community Multiscale Air Quality model using measurements from routine networks and the California Research at the Nexus of Air Quality and Climate Change 2010 campaign. The model correctly simulates broad spatial patterns of NH^(+)_(4) and NO^(-)_(3) including the elevated concentrations in eastern SoCAB. However, areas for model improvement have been identified. NH_3 emissions from livestock and dairy facilities appear to be too low, while those related to waste disposal in western SoCAB may be too high. Analyses using measurements from flights over SoCAB suggest that problems with NH3 predictions can influence NO^(-)_(3) predictions there. Offline ISORROPIA II calculations suggest that overpredictions of NH_x in Pasadena cause excessive partitioning of total nitrate to the particle phase overnight, while underpredictions of Na^+ cause too much partitioning to the gas phase during the day. Also, the model seems to underestimate mixing during the evening boundary layer transition leading to excessive nitrate formation on some nights. Overall, the analyses demonstrate fine-scale variations in model performance within and across the air basins. Improvements in inventories and spatial allocations of NH_3 emissions and in parameterizations of sea spray emissions, evening mixing processes, and heterogeneous ClNO_2 chemistry could improve model performance.

Inertial Particle Deposition in a Monkey Nasal Mold Compared with that in Human Nasal Replicas

Information on nasal particle deposition is used in risk assessments for exposure to airborne particulate pollutants and for optimizing the delivery of therapeutic aerosols. Monkeys are commonly used to assess the therapeutic potential of inhaled substances and to a lesser extent the toxicity of inhaled xenobiotics. Yet no reliable measurements of the deposition efficiency of monkey nasal airways for particles >1 μm have been reported to date. The goals of this study were to measure the deposition efficiency (>1 μm) of a replica of monkey nasal airways and to investigate potential differences in nasal deposition between humans and monkeys by comparing results with similar measurements recently reported for human nasal replicas. The monkey nasal replica was an acrylic mold made from a postmortem cast of the nasal airways of a 12-kg, male rhesus monkey. Particle deposition in the monkey nasal mold was measured for monodisperse aerosols between 1 and 10 μm and constant inspiratory flow rates between 2 and 7 lpm. Total deposition efficiency increased from nearly 0 to 100% with increasing particle inertia and was uniquely determined by values of an inertial impaction parameter. The deposition efficiencies of the monkey replica agreed well with those of human nasal replicas when compared according to equivalent Stokes numbers based on minimum cross-sectional area. Results from this study could improve monkey-to-human extrapolation models and interpretations of data from particle toxicity and therapeutic aerosol studies using monkeys.

Measurements and modeling of the inorganic chemical composition of fine particulate matter and associated precursor gases in California's San Joaquin Valley during CalNex 2010

A modified Ambient Ion Monitor-Ion Chromatograph was utilized to monitor the composition of water-soluble fine particulate matter (PM2.5) and precursor gases at the Bakersfield, CA, supersite during Research at the Nexus of Air Quality and Climate Change (CalNex) in May and June of 2010. The observations were used to investigate inorganic gas/particle partitioning, to derive an empirical relationship between ammonia emissions and temperature, and to assess the performance of the Community Multiscale Air Quality (CMAQ) model. The water-soluble PM2.5 maximized in the morning and in the evening because of gas/particle partitioning and possibly regional transport. Among the PM2.5 constituents, pNO3− was the dominant chemical species with campaign average mass loading of 0.80 µg m−3, and the mass loadings of pNH4+ and pSO42− were 0.46 µg m−3 and 0.53 µg m−3, respectively. The observed HNO3 (g) levels had an average of 0.14 ppb. Sub-ppb levels of SO2 (g) were measured, consistent with the absence of major emission sources in the region. Measured NH3 (g) had an average of 19.7 ppb over the campaign and demonstrated a strong relationship with temperature. Observations of ammonia were used to derive an empirical enthalpy for volatilization of 30.8 ± 2.1 kJ mol−1. The gas/particle partitioning of semivolatile PM2.5 composition was driven by meteorological factors and limited by total nitrate (TN) in this region. CMAQ model output exhibited significant biases in the predicted concentrations of pSO42−, NH3 (g), and TN. The largest model bias was in HNO3 (g), with an overprediction of an order of magnitude, which may be due to missing HNO3 (g) sinks such as reactive uptake on dust in the CMAQ framework.

Modeling community asbestos exposure near a vermiculite processing facility: Impact of human activities on cumulative exposure

Contaminated vermiculite ore from Libby, Montana was processed in northeast Minneapolis from 1936 to 1989 in a densely populated urban residential neighborhood, resulting in non-occupational exposure scenarios from plant stack and fugitive emissions as well as from activity-based scenarios associated with use of the waste rock in the surrounding community. The objective of this analysis was to estimate potential cumulative asbestos exposure for all non-occupationally exposed members of this community. Questionnaire data from a neighborhood-exposure assessment ascertained frequency of potential contact with vermiculite processing waste. Monte Carlo simulation was used to develop exposure estimates based on activity-based concentration estimates and contact durations for four scenarios: S1, moved asbestos-contaminated waste; S2, used waste at home, on lawn or garden; S3, installed/removed vermiculite insulation; S4, played in or around waste piles at the plant. The simulation outputs were combined with air-dispersion model results to provide total cumulative asbestos exposure estimates for the cohort. Fiber emissions from the plant were the largest source of exposure for the majority of the cohort, with geometric mean cumulative exposures of 0.02 fibers/cc × month. The addition of S1, S2 and S3 did not significantly increase total cumulative exposure above background exposure estimates obtained from dispersion modeling. Activity-based exposures were a substantial contributor to the upper end of the exposure distribution: 90th percentile S4 exposure estimates are ∼10 times higher than exposures from plant emissions. Pile playing is the strongest source of asbestos exposure in this cohort, with other activity scenarios contributing less than from plant emissions.

NASAL MOLDS AS PREDICTORS OF FINE AND COARSE PARTICLE DEPOSITION IN RAT NASAL AIRWAYS

Respiratory particle toxicity and accompanying dosimetry are commonly studied in laboratory animals and results are extrapolated to humans. Nasal deposition in the rat has been studied experimentally using acrylic molds made from postmortem casts and in vivo techniques. A previous study (Martonen & Yang, 1993) found agreement between the deposition efficiencies of rat nasal airways and nasal molds for ultrafine particles (<0.1 micro m) but disagreement for particles greater than 1 micro m. In this work, the hypothesis that molds made from postmortem casts of rat nasal airways are suitable predictors of the deposition of particles greater than 1 micro m in live rats was reevaluated by considering data recently obtained in our laboratory. Comparisons of deposition data for steady and pulsatile flows in the inspiratory and expiratory directions from studies using an F344 nasal mold and Long-Evans rats were performed. The validity of comparing nasal deposition data derived from an F344 nasal airway with data from Long-Evans airways was supported by a comparison of the nasal morphologies of these strains. Graphical comparisons of data showed good agreement between deposition in a nasal mold and rat nasal airways for particles with diameters between 0.5 and 4 micro m; statistical comparisons indicated differences. Statistical findings were not considered conclusive because of differences in variability between the studies. The available data suggest that good estimates of total nasal deposition in rats can be obtained by using rat nasal molds as surrogates for their live counterparts in studies of the deposition of particles greater than about 0.5 micro m.

Community Exposure to Asbestos From a Vermiculite Exfoliation Plant in NE Minneapolis

Western Mineral Products/W. R. Grace operated a vermiculite plant in a mixed industrial/ residential area of northeast Minneapolis from 1936 to 1989. The plant processed vermiculite ore contaminated with amphibole asbestos from a mine in Libby, MT. Air monitoring in the early 1970s found fiber concentrations in excess of 10 fibers per cubic centimeter of air (f/cc), indicating that worker exposure to asbestos was occasionally 100 times the current occupational standard. Residents of the surrounding community also had direct contact with vermiculite processing wastes (containing up to 10% amphibole asbestos) that were made freely available. Children played on waste piles and neighborhood residents hauled the wastes away for home use. In total, 259 contaminated residential properties have been found to date. Reported emission factors and plant process data were used as inputs to model airborne emissions from the plant over several operating scenarios using the U.S. Environmental Protection Agency (EPA) ISC-Prime model. Results estimate short-term air concentrations of asbestos fibers in residential areas nearest the plant may have at times exceeded current occupational standards. Exposure estimates for other pathways were derived primarily from assessments done in Libby by the U.S. EPA. The Northeast Minneapolis Community Vermiculite Investigation (NMCVI) was conducted by the Minnesota Department of Health to identify and characterize the exposures of a cohort of over 6000 people who live or lived in Northeast Minneapolis and may have been exposed to asbestos. This cohort is now being investigated in a respiratory health screening study conducted by the University of Minnesota and the Minnesota Department of Health.