Optical Modeling of Single Asian Dust and Marine Air Particles: A Comparison with Geometric Particle Shapes for Remote Sensing.

We compare the optical properties of various geometric shapes with single atmospheric Asian dust and marine background air particles collected at Mauna Loa Observatory. Three-dimensional representations of the particles were acquired with focused ion-beam (FIB) tomography, which involves FIB milling of individual particles followed by imaging and elemental mapping with scanning electron microscopy. Particles were heterogeneous with mainly dolomite or calcite and a minor amount of iron; marine air particles contained gypsum but no iron. Extinction and backscatter fraction were calculated with the discrete dipole approximation method. Geometric shapes were grouped as ellipsoids (sphere, spheroid, ellipsoid), cuboids (cube, square prism, rectangular prism), and pyramids (tetrahedron, triangular pyramid). Each group represented a progression of shapes with 1, 2, or 3 non-identical axes. Most shapes underestimated particle extinction and overestimated the backscatter fraction. Not surprisingly, extinction and the backscatter fraction of the sphere and cube were furthest from those of the particles. While the 3-axis ellipsoid and rectangular prism were closer dimensionally to the particles, extinction and the backscatter fraction for the 2-axis spheroid and square prism, respectively, were often closer to the particles. The extinction and backscatter fraction for the tetrahedron and triangular pyramid were closer on average to the actual particles than were the other shapes. Tetrahedra have the advantage that parameterization of an aerosol model for remote sensing would not require an aspect ratio distribution. Particle surface roughness invariably decreased the backscatter fraction. While surface roughness typically contributes a minor part to overall scattering, in some cases the larger surface area of the tetrahedron and triangular pyramid sufficiently accounted for enhanced forward scattering of particles from surface roughness.

Computerization, Obsolescence and the Length of Working Life.

This paper analyzes how computerization affected the labor market outcomes of older workers between 1984 and 2017. Using the computerization supplements of the Current Population Survey (CPS) we show that different occupations were computerized at different times, older workers tended to start using computers with a delay compared to younger workers, but computer use within occupations converged to the same levels across age groups eventually. That is, there was a temporary knowledge gap between younger and older workers in most occupations. We estimate how this knowledge gap affected older workers' labor market outcomes using data from the CPS and the Health and Retirement Study. Our models control for occupation and time fixed effects and in some models; we also control for full occupation-time interactions and use middle aged (age 40-49) workers as the control group. We find strong and robust negative effects of the knowledge gap on wages, and a large, temporary increase in transitions from work to non-participation, consistent with a model of creative destruction in which the computerization of jobs made older workers' skills obsolete in birth cohorts that experienced computerization relatively late in their careers. We find larger effects on females and on middle-skilled workers.

Perspectives and perceived barriers to pharmacist-prescribed tobacco cessation services in the community pharmacy setting.

OBJECTIVE(S): Tobacco use is a leading cause of preventable morbidity and mortality in the United States. Community pharmacists are in an advantageous position to increase patient accessibility to tobacco cessation medications and counseling. Pharmacists are permitted to prescribe or furnish tobacco cessation medications in 13 states with varying requirements and limitations. The primary objective of this study was to evaluate the perspectives and perceived barriers that pharmacy personnel have in providing pharmacist-prescribed tobacco cessation services in the community pharmacy setting. The secondary objectives were to evaluate current practices of the 5 A's model and to identify additional training needed to provide the service. METHODS: This study was a descriptive cross-sectional electronic survey of pharmacy personnel from a large grocery pharmacy chain. The respondents were asked about their demographics, current practices of the 5 A's model, perceived barriers and attitudes toward pharmacist-prescribed tobacco cessation services, and additional training needed to provide the service. RESULTS: The survey received 79 responses from pharmacists. The results showed that 92.4% (73/79) of the respondents agreed that community pharmacists should provide tobacco cessation services. The biggest barrier identified was "lack of time during normal workflow to deliver tobacco cessation services" at 54.4% (43/79). Regarding the 5 A's model, 74.7% (59/79) of the pharmacists responded "never" or "somewhat infrequently" to how often they practice the "Ask" step, with other steps in the 5 A's model reported at similar frequencies. The top 3 additional trainings that the pharmacists identified were "strategies developing a follow-up plan with patients," "incorporating service into workflow," and "strategies providing counseling on tobacco cessation." CONCLUSION: Efforts should be made to give community pharmacy personnel more time and guidance to provide patient care services beyond traditional dispensing roles to provide tobacco cessation services.

Evaluating patient satisfaction with pharmacist-administered long-acting injectable antipsychotics in the community pharmacy.

OBJECTIVE: To evaluate patient satisfaction with pharmacist-administered long-acting injectable antipsychotics (LAIAs) in the community pharmacy. DESIGN: Prospective survey. SETTING: Albertsons Companies community pharmacies during December 2016 to February 2017. PARTICIPANTS: Patients receiving LAIAs at participating pharmacies. MAIN OUTCOME MEASURES: A survey assessed patients' satisfaction with pharmacist-administered LAIAs in the community pharmacy. RESULTS: LAIA recipients (N = 104) reported satisfaction with community pharmacist-administered LAIAs. Participants who had received the service at other types of health clinics (N = 57) also reported higher satisfaction with current service compared to a similar service received elsewhere. Participants indicated that they would recommend service to others and that service was more convenient than a similar service received in an alternative setting. There was not a statistically significant relationship between patient demographic characteristics and likelihood of recommending service to others. CONCLUSION: Patients were satisfied with a pharmacist-administered LAIA service in the community pharmacy, and they found it more convenient than similar services provided elsewhere.

Performance of Passive Samplers Analyzed by Computer-Controlled Scanning Electron Microscopy to Measure PM10-2.5.

We report on the precision and accuracy of measuring PM10-2.5 and its components with particles collected by passive aerosol samplers and analyzed by computer-controlled scanning electron microscopy with energy dispersive X-ray spectroscopy. Passive samplers were deployed for week-long intervals in triplicate and colocated with a federal reference method sampler at three sites and for 5 weeks in summer 2009 and 5 weeks in winter 2010 in Cleveland, OH. The limit of detection of the passive method for PM10-2.5 determined from blank analysis was 2.8 µg m(-3). Overall precision expressed as root-mean-square coefficient of variation (CVRMS) improved with increasing concentrations (37% for all samples, n = 30; 19% for PM10-2.5 > 10 µg m(-3), n = 9; and 10% for PM10-2.5 > 15 µg m(-3), n = 4). The linear regression of PM10-2.5 measured passively on that measured with the reference sampler exhibited an intercept not statistically different than zero (p = 0.46) and a slope not statistically different from unity (p = 0.92). Triplicates with high CVs (CV > 40%, n = 5) were attributed to low particle counts (and mass concentrations), spurious counts attributed to salt particles, and Al-rich particles. This work provides important quantitative observations that can help guide future development and use of passive samplers for measuring atmospheric particulate matter.

Is it all worth it? The experiences of new PhDs on the job market, 2007-10.

This paper describes the job market experiences of new PhD economists, 2007-10. Using information from PhD programs' job candidate websites and original surveys, the authors present information about job candidates' characteristics, preferences and expectations; how job candidates fared at each stage of the market; and predictors of outcomes at each stage. Some information presented in this paper updates findings of prior studies. However, design features of the data used in this paper may result in more generalizable findings. This paper is unique in comparing pre-market expectations and preferences with post-market outcomes on the new PhD job market. It shows that outcomes tend to align with pre-market preferences, and candidates' expectations are somewhat predictive of their outcomes. Several analyses also shed light on sub-group differences.

Near-road modeling and measurement of cerium-containing particles generated by nanoparticle diesel fuel additive use.

Cerium oxide nanoparticles (nCe) are used as a fuel-borne catalyst in diesel engines to reduce particulate emissions, yet the environmental and human health impacts of the exhaust particles are not well understood. To bridge the gap between emission measurements and ambient impacts, size-resolved measurements of particle composition and mass concentration have been performed in Newcastle-upon-Tyne, United Kingdom, where buses have used an nCe additive since 2005. These observations show that the noncrustal cerium fraction thought to be associated with the use of nCe has a mass concentration ∼ 0.3 ng m(-3) with a size distribution peaking at 100-320 nm in aerodynamic diameter. Simulations with a near-roadway multicomponent sectional aerosol dynamic model predict that the use of nCe additives increases the number concentration of nuclei mode particles (<50 nm in diameter) while decreasing the total mass concentration. The near-road model predicts a downwind mass size distribution of cerium-containing particles peaking at 150 nm in aerodynamic diameter, a value similar to that measured for noncrustal cerium in Newcastle. This work shows that both the emission and atmospheric transformation of cerium-containing particles needs to be taken into account by regional modelers, exposure scientists, and policymakers when determining potential environmental and human health impacts.

Delayed management of acute type A aortic dissection with concomitant coronary artery bypass graft.

BACKGROUND: Pre-operative coronary angiography and concomitant, planned coronary artery bypass are infrequently performed with type A aortic dissection repair. We present a case in which pre-operative coronary computed tomography angiography was appropriate, and subsequent dissection repair and concomitant coronary artery bypass were successfully performed. CASE PRESENTATION: The patient is a 58-year-old male with heart failure with preserved ejection fraction, renal insufficiency, hypertension, obesity, and smoking history, who presented with a three-to-four-day history of persistent back pain, worsening exertional dyspnea, and orthopnea, as well as a two-to-three month history of dyspnea, lower extremity edema, and intermittent angina. He was diagnosed with an acute type A aortic dissection and anti-impulse control was initiated. However, repair was delayed in order to allow apixaban to metabolize and decrease the risk of bleeding, as the patient was approximately six days post-dissection, without malperfusion, with a well-controlled blood pressure on anti-impulse therapy, and had received five days of anticoagulation. During this time, coronary computed tomography angiography was performed to assess the need for concomitant revascularization and showed coronary artery disease. Ascending aorta hemiarch replacement with aortic valve resuspension, two-vessel coronary artery bypass grafting, and left atrial appendage clipping were performed successfully. CONCLUSIONS: Pre-operative imaging can be considered in a select group of acute type A aortic dissections that present without malperfusion, and with well-controlled blood pressure on anti-impulse/negative inotropic therapy.

Release of silver from nanotechnology-based consumer products for children.

We assessed the potential for children's exposure to bioavailable silver during the realistic use of selected nanotechnology-based consumer products (plush toy, fabric products, breast milk storage bags, sippy cups, cleaning products, humidifiers, and humidifier accessory). We measured the release of ionic and particulate silver from products into water, orange juice, milk formula, synthetic saliva, sweat, and urine (1:50 product to liquid mass ratio); into air; and onto dermal wipes. Of the liquid media, sweat and urine yielded the highest amount of silver release, up to 38% of the silver mass in products; tap water yielded the lowest amount, ≤1.5%. Leaching from a blanket into sweat plateaued within 5 min, with less silver released after washing. Between 0.3 and 23 µg m(-2) of silver transferred from products to wipes. Aerosol concentrations were not significantly elevated during product use. Fabrics, a plush toy, and cleaning products were most likely to release silver. Silver leached mainly via dissolution and was facilitated in media with high salt concentrations. Levels of silver to which children may potentially be exposed during the normal use of these consumer products is predicted to be low, and bioavailable silver is expected to be in ionic rather than particulate form.

Circulatory HMGB1 is an early predictive and prognostic biomarker of ARDS and mortality in a swine model of polytrauma.

Acute respiratory distress syndrome (ARDS) is a leading cause of morbidity and mortality in polytrauma patients. Pharmacological treatments of ARDS are lacking, and ARDS patients rely on supportive care. Accurate diagnosis of ARDS is vital for early intervention and improved outcomes but is presently delayed up to days. The use of biomarkers for early identification of ARDS development is a potential solution. Inflammatory mediators high-mobility group box 1 (HMGB1), syndecan-1 (SDC-1), and C3a have been previously proposed as potential biomarkers. For this study, we analyzed these biomarkers in animals undergoing smoke inhalation and 40% total body surface area burns, followed by intensive care for 72 h post-injury (PI) to determine their association with ARDS and mortality. We found that the levels of inflammatory mediators in serum were affected, as well as the degree of HMGB1 and Toll-like receptor 4 (TLR4) signal activation in the lung. The results showed significantly increased HMGB1 expression levels in animals that developed ARDS compared with those that did not. Receiver operating characteristic (ROC) analysis showed that HMGB1 levels at 6 h PI were significantly associated with ARDS development (AUROC=0.77) and mortality (AUROC=0.82). Logistic regression analysis revealed that levels of HMGB1 ≥24.10 ng/ml are associated with a 13-fold higher incidence of ARDS [OR:13.57 (2.76-104.3)], whereas the levels of HMGB1 ≥31.39 ng/ml are associated with a 12-fold increase in mortality [OR: 12.00 (2.36-93.47)]. In addition, we found that mesenchymal stem cell (MSC) therapeutic treatment led to a significant decrease in systemic HMGB1 elevation but failed to block SDC-1 and C3a increases. Immunohistochemistry analyses showed that smoke inhalation and burn injury induced the expression of HMGB1 and TLR4 and stimulated co-localization of HMGB1 and TLR4 in the lung. Interestingly, MSC treatment reduced the presence of HMGB1, TLR4, and the HMGB1-TLR4 co-localization. These results show that serum HMGB1 is a prognostic biomarker for predicting the incidence of ARDS and mortality in swine with smoke inhalation and burn injury. Therapeutically blocking HMGB1 signal activation might be an effective approach for attenuating ARDS development in combat casualties or civilian patients.

Single-particle SEM-EDX analysis of iron-containing coarse particulate matter in an urban environment: sources and distribution of iron within Cleveland, Ohio.

The physicochemical properties of coarse-mode, iron-containing particles and their temporal and spatial distributions are poorly understood. Single-particle analysis combining X-ray elemental mapping and computer-controlled scanning electron microscopy (CCSEM-EDX) of passively collected particles was used to investigate the physicochemical properties of iron-containing particles in Cleveland, OH, in summer 2008 (Aug-Sept), summer 2009 (July-Aug), and winter 2010 (Feb-March). The most abundant classes of iron-containing particles were iron oxide fly ash, mineral dust, NaCl-containing agglomerates (likely from road salt), and Ca-S containing agglomerates (likely from slag, a byproduct of steel production, or gypsum in road salt). The mass concentrations of anthropogenic fly ash particles were highest in the Flats region (downtown) and decreased with distance away from this region. The concentrations of fly ash in the Flats region were consistent with interannual changes in steel production. These particles were observed to be highly spherical in the Flats region, but less so after transport away from downtown. This change in morphology may be attributed to atmospheric processing. Overall, this work demonstrates that the method of passive collection with single-particle analysis by electron microscopy is a powerful tool to study spatial and temporal gradients in components of coarse particles. These gradients may correlate with human health effects associated with exposure to coarse-mode particulate matter.

The utility of pharmacokinetic-pharmacodynamic modeling in the discovery and optimization of selective S1P(1) agonists.

Sphingosine-1-phosphate (S1P(1)) receptor agonists such as Fingolimod (FTY-720) are a novel class of immunomodulators that have clinical utility in the treatment of remitting relapsing multiples sclerosis. This class of compound act by inducing peripheral lymphopenia. Using an integrated pharmacokinetic/pharmacodynamic (PK-PD) approach based on an in vivo rat model, novel S1P(1) agonists were identified with a predicted more rapid rate of reversibility of lymphocyte reduction in human compared to Fingolimod. The in vivo potency of 15 compounds based on PK-PD modelling of the rat lymphocyte reduction model was correlated with in vitro measures of potency at the S1P(1) receptor using ß arrestin recruitment and G-protein signalling. A structurally novel S1P(1) agonist was identified and predictions of human pharmacokinetics and clinical dose are presented.

Prehospital End-Tidal CO2: A Superior Marker for Mortality Risk in the Acutely Injured Patient.

BACKGROUND: Emergency medical personnel must expeditiously triage acutely injured patients to the appropriate medical facility. Efficient and objective variables to facilitate this process and provide information to the receiving trauma center are needed. Currently, multiple variables are used to prognosticate injury severity and risk of mortality including vital signs, mental status, lactate, and base excess. We investigated the prehospital use of end-tidal carbon dioxide (ETCO2) as a noninvasive physiologic measure that can be obtained in the acutely injured patient. METHODS: We performed a retrospective analysis of 557 acutely injured patients over 2 years at a Level 1 trauma center. All patients arriving as trauma activations with ETCO2 measurements were included in analysis. End-tidal carbon dioxide measurements were categorized as low, normal, and high based on reference levels. Mortality was the primary outcome. Secondary receiver operator curves (ROC) for base excess, venous lactate, blood pressure, and venous pH were compared. We hypothesized ETCO2 levels would be able to predict mortality. RESULTS: End-tidal carbon dioxide levels conferred a mortality rate of 38%, 17.3%, and 2.9% for low, normal, and high, respectively (P < .001). Receiver operator curve analysis produced an area under the curve predictive value for ETCO2 (.748) which was superior to lactate (.660), SBP (.578), pH (.560), and base excess (.497). DISCUSSION: End-tidal carbon dioxide is a more sensitive and specific predictor of mortality in the acutely injured patient compared to venous lactate, base deficit, blood pressure, or venous pH. Additional studies are needed to determine if ETCO2 can be used as an effective prehospital adjunct to prevent mortality in acutely injured patients.

Characterization of a fatty acyl-CoA reductase from Marinobacter aquaeolei VT8: a bacterial enzyme catalyzing the reduction of fatty acyl-CoA to fatty alcohol.

Fatty alcohols are of interest as a renewable feedstock to replace petroleum compounds used as fuels, in cosmetics, and in pharmaceuticals. One biological approach to the production of fatty alcohols involves the sequential action of two bacterial enzymes: (i) reduction of a fatty acyl-CoA to the corresponding fatty aldehyde catalyzed by a fatty acyl-CoA reductase, followed by (ii) reduction of the fatty aldehyde to the corresponding fatty alcohol catalyzed by a fatty aldehyde reductase. Here, we identify, purify, and characterize a novel bacterial enzyme from Marinobacter aquaeolei VT8 that catalyzes the reduction of fatty acyl-CoA by four electrons to the corresponding fatty alcohol, eliminating the need for a separate fatty aldehyde reductase. The enzyme is shown to reduce fatty acyl-CoAs ranging from C8:0 to C20:4 to the corresponding fatty alcohols, with the highest rate found for palmitoyl-CoA (C16:0). The dependence of the rate of reduction of palmitoyl-CoA on substrate concentration was cooperative, with an apparent K(m) ~ 4 µM, V(max) ~ 200 nmol NADP(+) min(-1) (mg protein)(-1), and n ~ 3. The enzyme also reduced a range of fatty aldehydes with decanal having the highest activity. The substrate cis-11-hexadecenal was reduced in a cooperative manner with an apparent K(m) of ~50 µM, V(max) of ~8 µmol NADP(+) min(-1) (mg protein)(-1), and n ~ 2.

Mental Retirement.

Some studies suggest that people can maintain their cognitive abilities through "mental exercise." This has not been unequivocally proven. Retirement is associated with a large change in a person's daily routine and environment. In this paper, we propose two mechanisms how retirement may lead to cognitive decline. For many people retirement leads to a less stimulating daily environment. In addition, the prospect of retirement reduces the incentive to engage in mentally stimulating activities on the job. We investigate the effect of retirement on cognition empirically using cross-nationally comparable surveys of older persons in the United States, England, and 11 European countries in 2004. We find that early retirement has a significant negative impact on the cognitive ability of people in their early 60s that is both quantitatively important and causal. Identification is achieved using national pension policies as instruments for endogenous retirement.

A review of selected engineered nanoparticles in the atmosphere: sources, transformations, and techniques for sampling and analysis.

A state-of-the-science review was undertaken to identify and assess sampling and analysis methods to detect and quantify selected nanomaterials (NMs) in the ambient atmosphere. The review is restricted to five types of NMs of interest to the Office of Research and Development Nanomaterial Research Strategy (U.S. Environmental Protection Agency): cerium oxide, titanium dioxide, carbon nanostructures (carbon nanotubes and fullerenes), zero-valent iron, and silver nanoparticles. One purpose was determining the extent to which present-day ultrafine sampling and analysis methods may be sufficient for identifying and possibly quantifying engineered NMs (ENMs) in ambient air. Conventional sampling methods for ultrafines appear to require modifications. For cerium and titanium, background levels from natural sources make measurement of ENMs difficult to quantify. In cases where field studies have been performed, identification from bulk analysis samples have been made. Further development of methods is needed to identify these NMs, especially in specific size fractions of ambient aerosols.

Alternative Retirement Paths and Cognitive Performance: Exploring the Role of Preretirement Job Complexity.

BACKGROUND AND OBJECTIVES: Recent research suggests that working longer may be protective of cognitive functioning in later life, especially for workers in low complexity jobs. As postretirement work becomes increasingly popular, it is important to understand how various retirement pathways influence cognitive function. The present study examines cognitive changes as a function of job complexity in the context of different types of retirement transitions. RESEARCH DESIGN AND METHODS: We use data from the Health and Retirement Study (HRS) to examine change in cognitive function for workers who have held low, moderate, and high complexity jobs and move through distinct retirement pathways-retiring and returning to work, partial retirement-compared with those who fully retire or remain full-time workers. Inverse probability weighted regression adjustment (a propensity score method) is used to adjust for selection effects. RESULTS: There are systematic variations in the relationships between work and cognitive performance as a function of job complexity and retirement pathways. All retirement pathways were associated with accelerated cognitive decline for workers in low complexity jobs. In contrast, for high complexity workers retirement was not associated with accelerated cognitive decline and retiring and returning to work was associated with modest improvement in cognitive functioning. DISCUSSION AND IMPLICATIONS: Both policy makers and individuals are beginning to embrace longer working lives which offer variety of potential benefits. Our findings suggest that continued full-time work also may be protective for cognitive health in workers who hold low complexity jobs.

Prevalence of cognitive impairment without dementia in the United States.

BACKGROUND: Cognitive impairment without dementia is associated with increased risk for disability, increased health care costs, and progression to dementia. There are no population-based prevalence estimates of this condition in the United States. OBJECTIVE: To estimate the prevalence of cognitive impairment without dementia in the United States and determine longitudinal cognitive and mortality outcomes. DESIGN: Longitudinal study from July 2001 to March 2005. SETTING: In-home assessment for cognitive impairment. PARTICIPANTS: Participants in ADAMS (Aging, Demographics, and Memory Study) who were age 71 years or older drawn from the nationally representative HRS (Health and Retirement Study). Of 1770 selected individuals, 856 completed initial assessment, and of 241 selected individuals, 180 completed 16- to 18-month follow-up assessment. MEASUREMENTS: Assessments, including neuropsychological testing, neurologic examination, and clinical and medical history, were used to assign a diagnosis of normal cognition, cognitive impairment without dementia, or dementia. National prevalence rates were estimated by using a population-weighted sample. RESULTS: In 2002, an estimated 5.4 million people (22.2%) in the United States age 71 years or older had cognitive impairment without dementia. Prominent subtypes included prodromal Alzheimer disease (8.2%) and cerebrovascular disease (5.7%). Among participants who completed follow-up assessments, 11.7% with cognitive impairment without dementia progressed to dementia annually, whereas those with subtypes of prodromal Alzheimer disease and stroke progressed at annual rates of 17% to 20%. The annual death rate was 8% among those with cognitive impairment without dementia and almost 15% among those with cognitive impairment due to medical conditions. LIMITATIONS: Only 56% of the nondeceased target sample completed the initial assessment. Population sampling weights were derived to adjust for at least some of the potential bias due to nonresponse and attrition. CONCLUSION: Cognitive impairment without dementia is more prevalent in the United States than dementia, and its subtypes vary in prevalence and outcomes.

Impact of mine waste on airborne respirable particulates in northeastern Oklahoma, United States.

Atmospheric dispersion of particles from mine waste is potentially an important route of human exposure to metals in communities close to active and abandoned mining areas. This study assessed sources of mass and metal concentrations in two size fractions of respirable particles using positive matrix factorization (U.S. Environmental Protection Agency [EPA] PMF 3.0). Weekly integrated samples of particulate matter (PM) 10 microm in aerodynamic diameter or less (PM10) and fine PM (PM2.5, or PM <2.5 microm in aerodynamic diameter) were collected at three monitoring sites, varying distances (0.5-20 km) from mine waste piles, for 58 consecutive weeks in a former lead (Pb) and zinc (Zn) mining region. Mean mass concentrations varied significantly across sites for coarse PM (PM10-PM2.5) but not PM2.5 particles. Concentrations of Pb and Zn significantly decreased with increasing distance from the mine waste piles in PM10-PM2.5 (P < 0.0001) and PM2.5 (P < 0.0005) fractions. Source apportionment analyses deduced five sources contributing to PM2.5 (mobile source combustion, secondary sulfates, mine waste, crustal/soil, and a source rich in calcium [Ca]) and three sources for the coarse fraction (mine waste, crustal/soil, and a Ca-rich source). In the PM2.5 fraction, mine waste contributed 1-6% of the overall mass, 40% of Pb, and 63% of Zn. Mine waste impacts were more apparent in the PM10-PM2.5 fraction and contributed 4-39% of total mass, 88% of Pb, and 97% of Zn. Percent contribution of mine waste varied significantly across sites (P < 0.0001) for both size fractions, with highest contributions in the site closest to the mine waste piles. Seasonality, wind direction, and concentrations of the Ca-rich source were also associated with levels of ambient aerosols from the mine waste source. Scanning electron microscopy results indicated that the PMF-identified mine waste source is mainly composed of Zn-Pb agglomerates on crustal particles in the PM10-PM2.5 fraction. In conclusion, the differential impacts of mine waste on respirable particles by size fraction and location should be considered in future exposure evaluations.

Analysis and Optical Modeling of Individual Heterogeneous Asian Dust Particles Collected at Mauna Loa Observatory.

We have determined optical properties of heterogeneous particles from aerosol samples collected at Hawaii's Mauna Loa Observatory. Back trajectories, satellite imagery, and composition differences among particles from scanning electron microscopy revealed a subset of particles with dolomite or calcite that likely came from Asia. Using focused ion-beam tomography and the discrete dipole approximation, we show how small amounts of an iron phase (oxide or carbonate), or in one case soot, affected extinction and scattering compared with particles of neat dolomite or calcite. We show how particles exhibit a range scattering values due to varying orientations of the inclusion phases. Extinction efficiencies for the heterogeneous particles with dolomite (3.47) and calcite (3.36) were 19% to 21% lower than extinction for marine background air particles (3.72). Extinction for the Asian dust was, however, generally higher than for the neat particles. Compared to iron carbonate, the presence of an absorbing iron oxide affected scattering in Asian dust particles even at the low oxide concentrations studied here (0.6% to 8.1%). Scattering efficiency decreased by <1% with a 1% increase in hematite but by 2% to 5% with magnetite. Asian dust scattered light strongly forward, but backscattering was 56% larger than for the marine background air particles. Backscattering in the Asian dust was also larger with magnetite than hematite. Single scattering albedo for Asian dust with hematite, magnetite, or soot averaged 0.96 ± 0.06 ( x ¯ ± s , n = 19 ) but was as low as 0.72 with a magnetite mass of 5.8%.