Backyard aerosol pollution monitors: foliar surfaces, dust enrichment, and factors influencing foliar retention.

Air pollution is one of the leading causes of death from noncommunicable diseases globally, and in Arizona, both mining activities and abandoned agriculture can generate erodible dust. This dust is transported via wind and can carry high amounts of toxic pollutants. Industry-adjacent communities, or "fenceline communities," are generally closer to the pollution sources and are disproportionally impacted by pollution, or in this case, dust. The dust transported from the mine settles into nearby rivers, gardens, and homes, and increases the concentrations of elements beyond their naturally occurring amounts (i.e., enriched). This study was built upon previous community science work in which plant leaves were observed to collect similar concentrations to an accepted dust collection method and illustrated promise for their use as low-cost air quality monitors in these communities. This work investigated the concentration of Na, Mg, Al, K, Ca, Mn, Co, Cu, Zn, Mo, and Ba in dust from the leaves of community-collected backyard and garden plants (foliar dust), as well as if certain variables affected collection efficacy. This assessment evaluated (1) foliar concentration versus surface area for 11 elements, (2) enrichment factor (EF) values and ratios, (3) comparisons of foliar, garden, and yard samples to US Geological Survey data, and (4) what variable significantly affected dust collection efficacy. The EF results indicate that many of the samples were enriched (anthropogenically contaminated) and that the foliar samples were generally more contaminated than the yard and garden soil samples. Leaf surface area was the most influential factor for leaf collection efficiency (p < 0.05) compared to plant family or sampling location. Further studies are needed that standardize the plant species and age and include multiple replicates of the same plant species across partnering communities. This study has demonstrated that foliar dust is enriched in the participating partnering communities and that plant leaf samples can serve as backyard aerosol pollution monitors. Therefore, foliar dust is a viable indicator of outdoor settled dust and aerosol contamination and this is an adoptable monitoring technique for "fenceline communities."

Phytoremediation Reduces Dust Emissions from Metal(loid)-Contaminated Mine Tailings.

Environmental and health risk concerns relating to airborne particles from mining operations have focused primarily on smelting activities. However, there are only three active copper smelters and less than a dozen smelters for other metals compared to an estimated 500000 abandoned and unreclaimed hard rock mine tailings in the US that have the potential to generate dust. The problem can also extend to modern tailings impoundments, which may take decades to build and remain barren for the duration before subsequent reclamation. We examined the impact of vegetation cover and irrigation on dust emissions and metal(loid) transport from mine tailings during a phytoremediation field trial at the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site. Measurements of horizontal dust flux following phytoremediation reveals that vegetated plots with 16% and 32% canopy cover enabled an average dust deposition of 371.7 and 606.1 g m-2 y-1, respectively, in comparison to the control treatment which emitted dust at an average rate of 2323 g m-2 y-1. Horizontal dust flux and dust emissions from the vegetated field plots are comparable to emission rates in undisturbed grasslands. Further, phytoremediation was effective at reducing the concentration of fine particulates, including PM1, PM2.5, and PM4, which represent the airborne particulates with the greatest health risks and the greatest potential for long-distance transport. This study demonstrates that phytoremediation can substantially decrease dust emissions as well as the transport of windblown contaminants from mine tailings.

Hygroscopic Properties and Respiratory System Deposition Behavior of Particulate Matter Emitted By Mining and Smelting Operations.

This study examines size-resolved physicochemical data for particles sampled near mining and smelting operations and a background urban site in Arizona with a focus on how hygroscopic growth impacts particle deposition behavior. Particles with aerodynamic diameters between 0.056-18 µm were collected at three sites: (i) an active smelter operation in Hayden, AZ, (ii) a legacy mining site with extensive mine tailings in Iron King, AZ, and (iii) an urban site, inner-city Tucson, AZ. Mass size distributions of As and Pb exhibit bimodal profiles with a dominant peak between 0.32 and 0.56 µm and a smaller mode in the coarse range (>3 µm). The hygroscopicity profile did not exhibit the same peaks owing to dependence on other chemical constituents. Submicrometer particles were generally more hygroscopic than supermicrometer ones at all three sites with finite water-uptake ability at all sites and particle sizes examined. Model calculations at a relative humidity of 99.5% reveal significant respiratory system particle deposition enhancements at sizes with the largest concentrations of toxic contaminants. Between dry diameters of 0.32 and 0.56 µm, for instance, ICRP and MPPD models predict deposition fraction enhancements of 171%-261% and 33%-63%, respectively, at the three sites.

Windblown Dust Deposition Forecasting and Spread of Contamination around Mine Tailings.

Wind erosion, transport and deposition of windblown dust from anthropogenic sources, such as mine tailings impoundments, can have significant effects on the surrounding environment. The lack of vegetation and the vertical protrusion of the mine tailings above the neighboring terrain make the tailings susceptible to wind erosion. Modeling the erosion, transport and deposition of particulate matter from mine tailings is a challenge for many reasons, including heterogeneity of the soil surface, vegetative canopy coverage, dynamic meteorological conditions and topographic influences. In this work, a previously developed Deposition Forecasting Model (DFM) that is specifically designed to model the transport of particulate matter from mine tailings impoundments is verified using dust collection and topsoil measurements. The DFM is initialized using data from an operational Weather Research and Forecasting (WRF) model. The forecast deposition patterns are compared to dust collected by inverted-disc samplers and determined through gravimetric, chemical composition and lead isotopic analysis. The DFM is capable of predicting dust deposition patterns from the tailings impoundment to the surrounding area. The methodology and approach employed in this work can be generalized to other contaminated sites from which dust transport to the local environment can be assessed as a potential route for human exposure.

Pollution Prevention through Peer Education: A Community Health Worker and Small and Home-Based Business Initiative on the Arizona-Sonora Border.

Government-led pollution prevention programs tend to focus on large businesses due to their potential to pollute larger quantities, therefore leaving a gap in programs targeting small and home-based businesses. In light of this gap, we set out to determine if a voluntary, peer education approach led by female, Hispanic community health workers (promotoras) can influence small and home-based businesses to implement pollution prevention strategies on-site. This paper describes a partnership between promotoras from a non-profit organization and researchers from a university working together to reach these businesses in a predominately Hispanic area of Tucson, Arizona. From 2008 to 2011, the promotora-led pollution prevention program reached a total of 640 small and home-based businesses. Program activities include technical trainings for promotoras and businesses, generation of culturally and language appropriate educational materials, and face-to-face peer education via multiple on-site visits. To determine the overall effectiveness of the program, surveys were used to measure best practices implemented on-site, perceptions towards pollution prevention, and overall satisfaction with the industry-specific trainings. This paper demonstrates that promotoras can promote the implementation of pollution prevention best practices by Hispanic small and home-based businesses considered "hard-to-reach" by government-led programs.

Use of lead isotopes to identify sources of metal and metalloid contaminants in atmospheric aerosol from mining operations.

Mining operations are a potential source of metal and metalloid contamination by atmospheric particulate generated from smelting activities, as well as from erosion of mine tailings. In this work, we show how lead isotopes can be used for source apportionment of metal and metalloid contaminants from the site of an active copper mine. Analysis of atmospheric aerosol shows two distinct isotopic signatures: one prevalent in fine particles (<1µm aerodynamic diameter) while the other corresponds to coarse particles as well as particles in all size ranges from a nearby urban environment. The lead isotopic ratios found in the fine particles are equal to those of the mine that provides the ore to the smelter. Topsoil samples at the mining site show concentrations of Pb and As decreasing with distance from the smelter. Isotopic ratios for the sample closest to the smelter (650m) and from topsoil at all sample locations, extending to more than 1km from the smelter, were similar to those found in fine particles in atmospheric dust. The results validate the use of lead isotope signatures for source apportionment of metal and metalloid contaminants transported by atmospheric particulate.

Size-resolved dust and aerosol contaminants associated with copper and lead smelting emissions: implications for emission management and human health.

Mining operations, including crushing, grinding, smelting, refining, and tailings management, are a significant source of airborne metal and metalloid contaminants such as As, Pb and other potentially toxic elements. In this work, we show that size-resolved concentrations of As and Pb generally follow a bimodal distribution with the majority of contaminants in the fine size fraction (<1 µm) around mining activities that include smelting operations at various sites in Australia and Arizona. This evidence suggests that contaminated fine particles (<1 µm) are the result of vapor condensation and coagulation from smelting operations while coarse particles are most likely the result of windblown dust from contaminated mine tailings and fugitive emissions from crushing and grinding activities. These results on the size distribution of contaminants around mining operations are reported to demonstrate the ubiquitous nature of this phenomenon so that more effective emission management and practices that minimize health risks associated with metal extraction and processing can be developed.

Spatiotemporal Distribution of Airborne Particulate Metals and Metalloids in a Populated Arid Region.

A statistical analysis of data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network of aerosol samplers has been used to study the spatial and temporal concentration trends in airborne particulate metals and metalloids for southern Arizona. The study region is a rapidly growing area in southwestern North America characterized by high fine soil concentrations (among the highest in the United States), anthropogenic emissions from an area within the fastest growing region in the United States, and a high density of active and abandoned mining sites. Crustal tracers in the region are most abundant in the summer (April - June) followed by fall (October - November) as a result of dry meteorological conditions which favor dust emissions from natural and anthropogenic activity. A distinct day-of-week cycle is evident for crustal tracer mass concentrations, with the greatest amplitude evident in urban areas. There have been significant reductions since 1988 in the concentrations of toxic species that are typically associated with smelting and mining. Periods with high fine soil concentrations coincide with higher concentrations of metals and metalloids in the atmosphere, with the enhancement being higher at urban sites.

Effect of wind speed and relative humidity on atmospheric dust concentrations in semi-arid climates.

Atmospheric particulate have deleterious impacts on human health. Predicting dust and aerosol emission and transport would be helpful to reduce harmful impacts but, despite numerous studies, prediction of dust events and contaminant transport in dust remains challenging. In this work, we show that relative humidity and wind speed are both determinants in atmospheric dust concentration. Observations of atmospheric dust concentrations in Green Valley, AZ, USA, and Juárez, Chihuahua, México, show that PM10 concentrations are not directly correlated with wind speed or relative humidity separately. However, selecting the data for high wind speeds (>4m/s at 10 m elevation), a definite trend is observed between dust concentration and relative humidity: dust concentration increases with relative humidity, reaching a maximum around 25% and it subsequently decreases with relative humidity. Models for dust storm forecasting may be improved by utilizing atmospheric humidity and wind speed as main drivers for dust generation and transport.

Modeling the emission, transport and deposition of contaminated dust from a mine tailing site.

Mining operations are potential sources of airborne particulate metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern US by climate models may make contaminated atmospheric dust and aerosols increasingly important, due to potential deleterious effects on human health and ecology. Dust emissions and dispersion of contaminants from the Iron King Mine tailings in Dewey-Humboldt, Arizona, a Superfund site, are currently being investigated through in situ field measurements and computational fluid dynamics modeling. These tailings are significantly contaminated with lead and arsenic with an average soil concentration of 1616 and 1420 ppm, respectively. Similar levels of these contaminants have also been measured in soil samples taken from the area surrounding the mine tailings. Using a computational fluid dynamics model, we have been able to model dust transport from the mine tailings to the surrounding region. The model includes a distributed Eulerian model to simulate fine aerosol transport and a Lagrangian approach to model fate and transport of larger particles. In order to improve the accuracy of the dust transport simulations both regional topographical features and local weather patterns have been incorporated into the model simulations.

Simulation of windblown dust transport from a mine tailings impoundment using a computational fluid dynamics model.

Mining operations are potential sources of airborne particulate metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern US by climate models may make contaminated atmospheric dust and aerosols increasingly important, due to potential deleterious effects on human health and ecology. Dust emissions and dispersion of dust and aerosol from the Iron King Mine tailings in Dewey-Humboldt, Arizona, a Superfund site, are currently being investigated through in situ field measurements and computational fluid dynamics modeling. These tailings are heavily contaminated with lead and arsenic. Using a computational fluid dynamics model, we model dust transport from the mine tailings to the surrounding region. The model includes gaseous plume dispersion to simulate the transport of the fine aerosols, while individual particle transport is used to track the trajectories of larger particles and to monitor their deposition locations. In order to improve the accuracy of the dust transport simulations, both regional topographical features and local weather patterns have been incorporated into the model simulations. Results show that local topography and wind velocity profiles are the major factors that control deposition.

Evidence of aqueous secondary organic aerosol formation from biogenic emissions in the North American Sonoran Desert.

This study examines the role of aqueous secondary organic aerosol formation in the North American Sonoran Desert as a result of intense solar radiation, enhanced moisture, and biogenic volatile organic compounds (BVOCs). The ratio of water-soluble organic carbon (WSOC) to organic carbon (OC) nearly doubles during the monsoon season relative to other seasons of the year. When normalized by mixing height, the WSOC enhancement during monsoon months relative to preceding dry months (May-June) exceeds that of sulfate by nearly a factor of 10. WSOC:OC and WSOC are most strongly correlated with moisture parameters, temperature, and concentrations of O3 and BVOCs. No positive relationship was identified between WSOC or WSOC:OC and anthropogenic tracers such as CO over a full year. This study points at the need for further work to understand the effect of BVOCs and moisture in altering aerosol properties in understudied desert regions.

Hygroscopic and chemical properties of aerosols collected near a copper smelter: implications for public and environmental health.

Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 µm) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 µm). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.

A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations.

Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.

An aerosol climatology for a rapidly growing arid region (southern Arizona): Major aerosol species and remotely sensed aerosol properties.

This study reports a comprehensive characterization of atmospheric aerosol particle properties in relation to meteorological and back trajectory data in the southern Arizona region, which includes two of the fastest growing metropolitan areas in the United States (Phoenix and Tucson). Multiple data sets (MODIS, AERONET, OMI/TOMS, MISR, GOCART, ground-based aerosol measurements) are used to examine monthly trends in aerosol composition, aerosol optical depth (AOD), and aerosol size. Fine soil, sulfate, and organics dominate PM2.5 mass in the region. Dust strongly influences the region between March and July owing to the dry and hot meteorological conditions and back trajectory patterns. Because monsoon precipitation begins typically in July, dust levels decrease, while AOD, sulfate, and organic aerosol reach their maximum levels because of summertime photochemistry and monsoon moisture. Evidence points to biogenic volatile organic compounds being a significant source of secondary organic aerosol in this region. Biomass burning also is shown to be a major contributor to the carbonaceous aerosol budget in the region, leading to enhanced organic and elemental carbon levels aloft at a sky-island site north of Tucson (Mt. Lemmon). Phoenix exhibits different monthly trends for aerosol components in comparison with the other sites owing to the strong influence of fossil carbon and anthropogenic dust. Trend analyses between 1988 and 2009 indicate that the strongest statistically significant trends are reductions in sulfate, elemental carbon, and organic carbon, and increases in fine soil during the spring (March-May) at select sites. These results can be explained by population growth, land-use changes, and improved source controls.

Metal and Metalloid Contaminants in Atmospheric Aerosols from Mining Operations.

Mining operations are potential sources of airborne metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern US by climate models may make contaminated atmospheric dust and aerosols increasingly important, with potential deleterious effects on human health and ecology. Fine particulates such as those resulting from smelting operations may disperse more readily into the environment than coarser tailings dust. Fine particles also penetrate more deeply into the human respiratory system, and may become more bioavailable due to their high specific surface area. In this work, we report the size-fractionated chemical characterization of atmospheric aerosols sampled over a period of a year near an active mining and smelting site in Arizona. Aerosols were characterized with a 10-stage (0.054 to 18 µm aerodynamic diameter) multiple orifice uniform deposit impactor (MOUDI), a scanning mobility particle sizer (SMPS), and a total suspended particulate (TSP) collector. The MOUDI results show that arsenic and lead concentrations follow a bimodal distribution, with maxima centered at approximately 0.3 and 7.0 µm diameter. We hypothesize that the sub-micron arsenic and lead are the product of condensation and coagulation of smelting vapors. In the coarse size, contaminants are thought to originate as aeolian dust from mine tailings and other sources. Observation of ultrafine particle number concentration (SMPS) show the highest readings when the wind comes from the general direction of the smelting operations site.

Kinetics and mechanism of the reaction of sodium azide with hypochlorite in aqueous solution.

Production of toxic sodium azide (NaN(3)) surged worldwide over the past two decades to meet the demand for automobile air bag inflator propellant. Industrial activity and the return of millions of inflators to automobile recycling facilities are leading to increasing release of NaN(3) to the environment so there is considerable interest in learning more about its environmental fate. Water soluble NaN(3) could conceivably be found in drinking water supplies so here we describe the kinetics and mechanism of the reaction of azide with hypochlorite, which is often used in water treatment plants. The reaction stoichiometry is: HOCl + 2N(3)(-) = 3N(2) + Cl(-) + OH(-), and proceeds by a key intermediate chlorine azide, ClN(3), which subsequently decomposes by reaction with a second azide molecule in the rate determining step: ClN(3) + N(3)(-) --> 3N(2) + Cl(-) (k = 0.52+/-0.04 M(-1) s(-1), 25 degrees C, mu = 0.1 M). We estimate that the half-life of azide would be approximately 15 s at the point of chlorination in a water treatment plant and approximately 24 days at some point downstream where only residual chlorine remains. Hypochlorite is not recommended for treatment of concentrated azide waste due to formation of the toxic chlorine azide intermediate under acidic conditions and the slow kinetics under basic conditions.

Interaction of Perchloroethylene with Cerium Oxide in Three-Way Catalysts.

The role of cerium oxide on direct oxidation of perchloroethylene (PCE) by a three-way catalyst was explored. In the absence of an external oxidizing agent, PCE was oxidized over an alumina supported Pt/Rh three-way catalyst. We hypothesize that the chlorine atoms in the adsorbed PCE interact with oxygen in CeO(2), reducing the cerium to create CeCl(3).

Catalytic Dechlorination of Gas-phase Perchloroethylene under Mixed Redox Conditions.

The validity of a new method to destroy gas-phase perchloroethylene (PCE) is demonstrated at bench scale using a fixed-bed reactor that contains a Pt/Rh catalyst. Hydrogen and oxygen were simultaneously fed to the reactor together with PCE. The conversion efficiencies of PCE were sensitive to H(2)/O(2) ratio and reactor temperature. When the temperature was >/= 400 degrees C and H(2)/O(2) was >/= 2.15, PCE conversion efficiency was maintained at >/= 90%. No catalyst deactivation was observed for over two years, using only mild, convenient regeneration procedures. It is likely that PCE reduction steps precede oxidation reactions and that the importance of oxidation lies in its elimination of intermediates that would otherwise lead to catalyst poisoning. In practice, this catalytic dechlorination method holds potential for low-cost, large-scale field operation.

Destruction of gas-phase trichloroethylene in a modified fuel cell.

A conventional fuel cell was used as a catalytic reactor to treat soil vapor extraction (SVE) gases contaminated with trichloroethylene (TCE). The SVE gases are fed to the cathode side of the fuel cell, where TCE is reduced to ethane and hydrochloric acid. The results obtained suggest that TCE reduction occurs by a catalytic reaction with hydrogen that is re-formed on the cathode's surface beyond a certain applied cell potential. Substantial conversion of TCE is obtained, even when competing oxygen reduction occurs in the cathode. The process has been modeled successfully by conceptualizing the flow passage in the fuel cell as a plug flow reactor.