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At least 163 records · Page 9

Funding a Just Transition Away from Coal in the U.S. Considering Avoided Damage from Air Pollution

Abstract Coal is declining in the U.S. as part of the clean energy transition, resulting in remarkable air pollution benefits for the American public and significant costs for the industry. Using the AP3 integrated assessment model, we estimate that fewer emissions of sulfur dioxide, nitrogen oxides, and primary fine particulate matter driven by coal’s decline led to $300 billion in benefits from 2014 to 2019. Conversely, we find that job losses driven by less coal plant and mining activity resulted in $7.84 billion in foregone wages over the same timeframe. While the benefits were greatly distributed (mostly throughout the East), costs were highly concentrated in coal communities. Transferring a small fraction of the benefits to workers could cover these costs while maintaining societal net benefits. Forecasting coal fleet damages from 2020 to 2035, we find that buying out or replacing these plants would result in $589 billion in air quality benefits, which considerably outweigh the costs. The return on investment increases when policy targets the most damaging capacity, and net benefits are maximized when removing just facilities where marginal benefits exceed marginal costs. Evaluating competitive reverse auction policy designs akin to Germany’s Coal Exit Act, we find that adjusting bids based on monetary damages rather than based only on carbon dioxide emissions – the German design – provides a welfare advantage. Our benefit–cost analyses clearly support policies that drive a swift and just transition away from coal, thereby clearing the air while supporting communities needing assistance.

Dennin, Luke R. (ORCID:0000000205405520)↗

Aerosol Optical Tweezers Elucidate the Chemistry, Acidity, Phase Separations, and Morphology of Atmospheric Microdroplets

Aerosol particles represent unique chemical environments because of their high surface area-to-volume ratio that promotes the effects of interfacial chemistry in confined environments. Properties such as viscosity, diffusivity, water content, pH, and morphology—following liquid–liquid phase separation—can strongly alter how a particle interacts with condensable vapors and reactive trace gases, thus modifying its continual evolution and environmental effects. Our understanding of this chemical evolution of atmospheric particulate matter and its environmental impacts is largely limited by our ability to directly observe how these critical particle properties respond to the addition or reactive uptake of new chemical components. Aerosol optical tweezers (AOT) stably trap particles in focused laser beams, providing positional control and the retrieval of many of these critical properties required to understand and predict the chemistry of aerosolized microdroplets. The analytical power of the AOT stems from the retrieval of the cavity-enhanced Raman spectrum induced by the trapping laser. Analysis of the whispering gallery modes (WGMs) that resonate as a standing wave around the droplet’s interface, provide high accuracy measurements of the droplet’s size, refractive index (and thus a measurement of composition), and can distinguish between core–shell, partially engulfed, and homogeneous morphologies. In this study, we have advanced the ability to determine the properties of the core and shell phases in biphasic droplets, including obtaining high-accuracy pH measurements. These capabilities were applied to perform AOT physical chemistry experiments on authentic secondary organic aerosol (SOA) produced directly in the AOT chamber by ozonolysis of terpene vapors. The propensity of the SOA to phase separate as a shell from a wide range of nonpolar to polar core phases was observed, along with the discovery of a stable emulsified state of SOA particles in an aqueous salt droplet. Micron-thick SOA shells did not impede the gain or loss of water or squalane from the core to the surrounding air, indicating no significant diffusional limitations to condensational growth or partitioning even under dry conditions. These experiments formed the foundation of a new framework that predicts how the phase-separated morphology of complex aerosols containing organic carbon evolves during continual atmospheric oxidation processes. Increases in oxidation state will quickly drive conversion from a partially engulfed to core–shell morphology that has dramatically different chemical reactivity since the core phase is completely concealed by the shell. The recent advances in the experimental capabilities of the AOT technique such as presented here enable novel experimental methodologies that provide insights into the chemistry and multidimensional properties of aerosol microdroplets, and how these coevolve and respond to continual chemical reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Impact of Biofuel Blends on Black Carbon Emissions from a Gas Turbine Engine

With a view towards renewable feedstock while decreasing the CO2 footprint associated with jet travel, biofuels are receiving increasing interest. Presented here is an overview of non-volatile particulate matter (nvPM) emissions, i.e. “soot” as gauged by varied TEM analyses for a J-85 turbojet fueled with Jet-A as well as with blends of Jet-A using Camelina biofuel. A unifying explanation is provided encompassing fuels and spanning length scales across three orders of magnitude. The variation of primary particle size, aggregate size and nanostructure are analyzed as a function of biofuel blend across range of engine thrust levels. The postulate is based on where fuels start along the soot formation pathway. Increasing biofuel content lowers aromatic concentration while placing increasing dependence upon fuel pyrolysis reactions to form the requisite concentration of aromatics for particle inception and growth. The required “kinetic” time for pyrolysis reactions to produce benzene and multi-ring PAHs allows increased fuel-air mixing by turbulence, diluting the fuel-rich soot-forming regions, effectively lowering their equivalence ratio. With a lower precursor concentration, particle inception is slowed, the resulting concentration of primary particles is lowered and smaller aggregates. The lower equivalence ratio also results in smaller primary particles given the lower concentration of growth species.

Kumal, Raju R.↗

Modeling Ethanol-Blend Fuel Sprays under Direct-Injection Spark-Ignition Engine Conditions

Computational modeling of fuel-injection and fuel-impingement processes was carried out to provide insight into previous experimental results obtained from a direct-injection spark-ignition research engine operated with various ethanol and aromatic fuel blends. Seven model fuels were evaluated using both single- and split-injection strategies. Model results showed that droplet vaporization enriched the concentrations of aromatic species in the liquid phase, especially those with low vapor pressure, and ethanol-containing fuels altered droplet sizes and led to increased liquid-phase mass in the cylinder. For the spray-modeling conditions studied, most of the injected fuel remained in the liquid phase, which would be expected to result in more fuel impingement on cylinder or piston surfaces. Fuel impinging on lower cylinder-temperature surfaces was found to create wall films that could interact with the piston during the compression stroke. Fuel impinging on hotter piston-temperature surfaces vaporized more readily, but for fuels with high ethanol and aromatic content, wall films remained and were highly concentrated with lower vapor pressure and aromatic compounds. These films could lead to pool fires during combustion and therefore significant particulate matter emissions.

BIOMASS FUELS,INORGANIC, ORGANIC, PHYSICAL, AND AN↗

Well-to-Wheels Analysis of Zero-Emission Plug-In Battery Electric Vehicle Technology for Medium- and Heavy-Duty Trucks

Conventional diesel medium- and heavy-duty vehicles (MHDVs) create large amount of air emissions. With the advancement in technology and reduction in the cost of batteries, plug-in battery electric vehicles (BEVs) are increasingly attractive options for improving energy efficiency and reducing air emissions of MHDVs. In this paper, we compared the well-to-wheels (WTW) greenhouse gases (GHGs) and criteria air pollutant emissions of MHD BEVs with their conventional diesel counterparts across weight classes and vocations. We expanded the Greenhouse gases, Regulated Emissions, and Energy use in Technologies (GREET) model to conduct the WTW analysis of MHDVs. The fuel economy for a wide range of MHDV weight classes and vocations, over various driving cycles, was evaluated using a high-fidelity vehicle dynamic simulation software (Autonomie). The environmental impacts of MHD BEVs are sensitive to the source of electricity used to recharge their batteries. The WTW results show that MHD BEVs significantly improve environmental sustainability of MHDVs by providing deep reductions in WTW GHGs, nitrogen oxides, volatile organic compounds, and carbon monoxide emissions, compared to conventional diesel counterparts. Increasing shares of renewable and natural gas technologies in future national and regional electricity generation are expected to reduce WTW particulate matters and sulfur oxide emissions for further improvement of the environmental performance of MHD BEVs.

33 ADVANCED PROPULSION SYSTEMS↗

Integrated Modeling of U.S. Agricultural Soil Emissions of Reactive Nitrogen and Associated Impacts on Air Pollution, Health, and Climate

Agricultural soils are leading sources of reactive nitrogen (Nr) species including nitrogen oxides (NO x ), ammonia (NH 3 ), and nitrous oxide (N 2 O). Here, the propensity of NO x and NH 3 to generate ozone and fine particulate matter (PM) and associated impacts on health are highly variable, whereas the climate impacts of long-lived N 2 O are independent of emission timing and location. However, these impacts have rarely been compared on a spatially-resolved, monetized basis. In this study, we update the nitrogen scheme in an agroecosystem model to simulate the agricultural emissions of Nr from across the United States. We then apply a reduced-form air pollution health effects model to assess air quality impacts from NO x and NH 3 and a social cost of N 2 O to assess the climate impacts. Assuming an $\$$8.2 million Value of a Statistical Life (VSL) and a $\$$13,100/ton social cost of N 2 O, the air quality impacts are a factor of ~7 to 15 times as large as the climate impacts in heavily populated coastal regions, whereas the ratios are closer to 2.5 in sparsely populated regions. Our results show that air pollution, health, and climate should be considered jointly in future assessments of how farming practices affect Nr emissions.

54 ENVIRONMENTAL SCIENCES↗

Characterizing PM 2.5 Emissions and Temporal Evolution of Organic Composition from Incense Burning in a California Residence

The chemical composition of incense-generated organic aerosol in residential indoor air has received limited attention in Western literature. In this study, we conducted incense burning experiments in a single-family California residence during vacancy. Here, we report the chemical composition of organic fine particulate matter (PM 2.5 ), associated emission factors (EFs), and gas-particle phase partitioning for indoor semivolatile organic compounds (SVOCs). Speciated organic PM 2.5 measurements were made using two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC×GC-HR-ToF-MS) and semivolatile thermal desorption aerosol gas chromatography (SV-TAG). Organic PM 2.5 EFs ranged from 7 to 31 mg g –1 for burned incense and were largely comprised of polar and oxygenated species, with high abundance of biomass-burning tracers such as levoglucosan. Differences in PM 2.5 EFs and chemical profiles were observed in relation to the type of incense burned. Nine indoor SVOCs considered to originate from sources other than incense combustion were enhanced during incense events. Time-resolved concentrations of these SVOCs correlated well with PM 2.5 mass (R 2 > 0.75), suggesting that low-volatility SVOCs such as bis(2-ethylhexyl)phthalate and butyl benzyl phthalate partitioned to incense-generated PM 2.5 . Both direct emissions and enhanced partitioning of low-volatility indoor SVOCs to incense-generated PM 2.5 can influence inhalation exposures during and after indoor incense use.

54 ENVIRONMENTAL SCIENCES↗

Techno-Economic Analysis and Life Cycle Assessment of Alternative Fuels for Locomotives in the U.S. Freight Rail Sector

Freight rail is more energy-efficient than truck transport over long-haul distances, offering a low-energy and emissions-intensive option for transporting freight. This study evaluates techno-economic analysis and life cycle assessment of seven alternative unblended fuels for freight locomotive engines─biodiesel, renewable diesel (RD), bio-oils, methanol, dimethyl ether (DME), ethanol, and ammonia─across 16 fuel pathways utilizing soybean, corn, woody biomass, renewable hydrogen, and waste sources, e.g., sludge, manure, and industrial CO 2 , and compares these to conventional diesel. The minimum fuel selling price (MFSP) ranged from $\$2.05$ to $\$8.27$ per diesel gallon equivalent (2020 US dollars), with biocrude and RDs produced from hydrothermal liquefaction (HTL) of sludge having the lowest MFSPs due to coproduct credits and avoided waste treatment cost. Life cycle GHG emissions ranged from −41 to 53 g of CO 2 e/MJ. RD from waste via HTL achieves negative emissions by diverting sludge/manure from GHG-intensive conventional management. Few pathways such as biocrude, methanol, and DME require additional control for SO X emissions in the refinery, while ethanol, FT-diesel, and bio-oil require additional control for particulate matter emissions. Bio-oil and RD from sludge have lower marginal abatement cost or MAC (–$\$38$/tonne CO 2 lowest) while methanol and ammonia with renewable hydrogen have higher MAC ($\$490$/tonne CO 2 maximum).

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

Life Cycle Assessment of Methanol from Fossil, Biomass, and Waste Sources, and Its Use as a Marine Fuel in Dual-Fuel Engines

Methanol is gaining interest in the marine sector from energy security and reducing emissions perspective. This study provides a comparative life cycle assessment of methanol as a marine fuel, across GHG and criteria air pollutant emission metrics, when it is used in a dual-fuel engine. Twelve methanol pathways from four different feedstock categories were considered, including (1) cellulosic biomass forest residues and clean pine mix, corn stover, switchgrass, and miscanthus; (2) organic wastes renewable natural gas from wastewater sludge, swine manure, food waste, and landfill gas; (3) fossil resources coal and natural gas (NG); and (4) e-methanol using captured carbon dioxide. When used in a dual-fuel engine with pilot fuel, life cycle GHG emissions for woody biomass-based methanol were approximately 19 gCO 2 e MJ −1 , while emissions from waste-based sources ranged between −154 and 31 gCO 2 e MJ −1 . Methanol from renewable sources showed a GHG reduction potential between 58 and 226% compared to conventional NG-based methanol (122 gCO 2 e MJ −1 ), primarily due to the avoided emissions from conventional waste management. When carbon from process emissions were captured, the reduction could be up to 327%. All pathways exhibited lower NO X , and particulate matter emissions compared to the baseline marine fuel (MGO 0.1% sulfur), while woody biomass and coal pathways had higher SO X emissions.

09 BIOMASS FUELS↗

Large-Scale Carbon Removal Will Create Public Health, Economic, and Climate Tradeoffs

Economy-wide efforts to achieve net-zero emissions offer both climate and air quality-related public health benefits from reducing fossil fuel combustion. We explore the expected costs and benefits if carbon dioxide removal (CDR) is deployed at scale in support of these efforts. Six leading forms of CDR at two levels of deployment are compared to a scenario with no U.S. climate action. We find that heavy reliance on CDR avoids a $2.5-5.8 trillion USD2020 in climate damages, provides $2.8-6.5 trillion USD2020 public health benefits, returns $5-6 trillion USD2020 in CDR revenues, but requires $11-13 trillion USD2020 CO2 mitigation cost, cumulatively by 2050 in the U.S. In contrast, lower reliance on CDR requires much deeper near-term fossil-fuel reductions, which increases mitigation costs by 52% but also creates 26% higher public health benefits from reductions in particulate matter- and ozone-related mortality and morbidity, preventing about 12,600 premature deaths by mid-century in the U.S.

Javadi, Parisa↗

Air Emissions Impacts of Fuel Substitution in the United States Cement Industry

High-heat industrial processes cannot be easily electrified, often rely on comparatively high-emitting solid fuels, and are essential for economic growth. Cement production in particular is critical to supporting construction and the expansion and maintenance of infrastructure systems in countries around the world. Fuels for cement production include petcoke, coal, and waste solvents, and their combustion contributes approximately 40% of the CO 2 emissions from global cement production. Broadening the fuel resources to include agricultural residues and other wastes can reduce emissions and divert waste from landfills. We assess the potential to use 16 different alternative fuels across the 88 integrated cement plants in the United States. The share of alternative fuels in the cement production sector could increase from the current level of 17% to as high as 73%. Fuel substitution can reduce the current fuel-related life-cycle emissions (28.6 ± 5.7 Mton CO 2 /year) by 19–45%. The greatest national-scale human health cobenefits occur when alternative fuels are prioritized at facilities currently using coal and petcoke. NO x emissions outcomes from this strategy are mixed, but SO x and particulate matter emissions reductions drive net human health benefits. These results suggest that targeted fuel substitution in heavy industries can yield outsized emissions benefits.

alternative fuels↗

Photolysis Controls Atmospheric Budgets of Biogenic Secondary Organic Aerosol

Secondary organic aerosol (SOA) accounts for a large fraction of tropospheric particulate matter. While SOA production rates and mechanisms have been extensively investigated, loss pathways remain uncertain. Most large-scale chemistry and transport models account for mechanical deposition of SOA, but not chemical losses, such as photolysis. There is also a paucity of laboratory measurements of SOA photolysis, which limits how well photolytic losses can be modeled. Here we show, through a combined experimental and modeling approach, that photolytic loss of SOA mass significantly alters SOA budget predictions. Using environmental chamber experiments, we find that SOA produced from several biogenic volatile organic compounds (VOCs) undergoes photolysis-induced mass loss at rates between 0 and 2.2% ± 0.4% of nitrogen dioxide (NO 2 ) photolysis, equivalent to average atmospheric lifetimes as short as 10 hours. We incorporate our photolysis rates into a regional chemical transport model to test the sensitivity of predicted SOA mass concentrations to photolytic losses. The addition of photolysis at rates consistent with our experimental conditions causes a ~50% reduction in biogenic SOA loadings over the Amazon, indicating that photolysis exerts a substantial control over the atmospheric SOA lifetime, with a likely dependence upon SOA molecular composition and thus production mechanisms.

54 ENVIRONMENTAL SCIENCES↗

Persistent Heavy Winter Nitrate Pollution Driven by Increased Photochemical Oxidants in Northern China

Nitrate is an increasingly important component of fine particulate matter (PM2.5) during winter in northern China. Past emission control has been ineffective in reducing winter nitrate. Here, we use extensive observations and a model with state-of-theart nitrogen chemistry to identify the key factors that control the nitrate formation in the heavily polluted North China Plain (NCP). In contrast to the previous view of weak winter photochemistry, we show that the O3 and OH productions are sufficiently high in winter to facilitate fast gas-phase and heterogeneous conversion of NOX to nitrate over the NCP. Increasing O3 and OH productions from higher precursor levels and fast ROX cycling accelerate the nitrate generation during heavy pollution. We find that the 31.8% reduction of NOX emissions from 2010 to 2017 in the NCP lowers surface nitrate by only 0.2% and even increases nitrate in some polluted areas. This is mainly due to the increase of O3 and OH (by~30%), which has subsequently increased the conversion efficiency of NOX to HNO3 (by 38.7%). Future control strategies for the winter haze should also aim to lower photochemical oxidants, via larger and synchronized NOX and VOCs emissions reduction, to overcome the effects of nonlinear photochemistry and aerosol chemical feedback.

Fu, Xiao↗

Atmospheric Brown Carbon on the Tibetan Plateau: Regional Differences in Chemical Composition and Light Absorption Properties

In this work, fine particulate matter (PM 2.5 ) filter samples were collected from two high-altitude remote sites located in the southern (QOMS) and northern (WLG) regions of the Tibetan Plateau (TP) to explore the regional differences in brown carbon (BrC) properties. Chemical differences in BrC composition representative of these two areas were inferred from molecular-level analysis of the PM 2.5 samples using high-performance liquid chromatography coupled with photodiode array and high-resolution mass spectrometry detectors. The results show that more polar BrC chromophores were abundant in QOMS samples, while contributions from polar and less polar chromophores were comparable in WLG samples. A higher mass absorption coefficient of BrC was observed at QOMS than at WLG. Strong BrC chromophores in QOMS samples were identified as oxygenated aromatics and nitrophenol compounds, while organosulfate compounds were found in the WLG sample. The results of this study indicate regional differences in BrC chromophores and provide insights into their sources and chemical processes, which should be considered for predictive understanding and modeling of the radiative forcing of aerosol in the TP area.

54 ENVIRONMENTAL SCIENCES↗

Wildland Urban Interface (WUI) Emissions: Laboratory Measurement of Aerosol and Trace Gas from Combustion of Manufactured Building Materials

Wildfires are increasing in intensity and more often threatening the wildland urban interface (WUI) where buildings and homes coexist with the natural environment. WUI emissions have not been as well-studied as emissions from vegetation. Thus, there is a need to quantify the emissions of building materials used in home construction under flaming and smoldering conditions to study their impacts to human health, visibility, air quality, and climate. Here, in a controlled laboratory setting, we quantify emissions of aerosols and trace gases including formaldehyde, particulate matter, and black carbon. We focus on the combustion of traditional single-source wood-based construction fuels. Our results indicate that, similar to natural fuels, the aerosol optical properties were more related to combustion conditions than the fuel type. Overall, we observed significant variability in the gas and particle emissions. Consistent trends include high formaldehyde (HCHO) and carbon monoxide (CO) emissions for smoldering conditions and higher carbon dioxide (CO 2 ), nitrogen oxides (NO x ), and black carbon for flaming conditions. Finally, these observations highlight the need to better characterize emissions for materials in the built environment to assess large-scale climate and human health impacts of fires at the WUI.

54 ENVIRONMENTAL SCIENCES↗

Field Evaluation of Do-It-Yourself Air Filtration Solutions for Evaporative Coolers to Reduce Ambient Particle Infiltration in Homes in Wildfire-Affected Communities

Evaporative coolers (ECs) introduce outdoor air pollutants indoors when operating. This study evaluates the potential of do-it-yourself (DIY) air filtration solutions for ECs to cost-effectively reduce the infiltration of ambient fine particulate matter (PM2.5) in homes with ECs using measurements in 48 homes in wildfire-affected agricultural communities in California. All homes received one portable air cleaner (PAC); 25 homes also received DIY filters (mostly MERV 13) attached to their ECs. PurpleAir monitors measured indoor and outdoor PM2.5 concentrations. PAC operation was monitored in all of the homes. EC usage was monitored in some homes and predicted using relative humidity dynamics in all homes. Conditional analyses between EC likely on and off conditions were used to evaluate the impacts of DIY EC filters on ambient PM2.5 infiltration, including during several wildfire-affected days. Median levels of ambient PM2.5 infiltration increased ∼36-42% in homes with only PAC interventions when ECs were likely operating compared to only ∼10-11% in homes with both PACs and DIY EC filters. Pre/postintervention comparisons in a subset of homes confirmed PM2.5 infiltration reductions. EC filter performance declined after extended use. Results suggest that short-term EC filter deployments are likely a cost-effective way to mitigate wildfire smoke infiltration inside these homes.

Wang, Mingyu↗

Wildfire‐Smoke Aerosols Lead to Increased Light Use Efficiency Among Agricultural and Restored Wetland Land Uses in California's Central Valley

Abstract There are few observational studies measuring the ecosystem‐scale productivity effects of changes in incident diffuse photosynthetically active radiation (PAR diffuse ), especially related to wildfire smoke. Climate change‐induced increases to the duration and intensity of fire conditions have made smoke a common occurrence across western North America, with largely unquantified ecosystem feedbacks. Under equivalent amounts of radiation, increased atmospheric particulate matter could lead to a boost in productivity as scattering redistributes photons throughout multilayer canopies. In this work, we leverage a meso‐network of eddy covariance measurement sites across a unique array of managed and restored C 3 and C 4 canopy types to understand how recent wildfire smoke affected ecosystem productivity during the summer of 2018, an especially smoky year in the agriculturally productive Central Valley. We find that diffuse PAR diffuse increased by more than a third compared to the previous growing season, while total PAR was only slightly diminished. These conditions caused nearly a doubling of light use efficiency over the range of diffuse fraction observed, with the highest sensitivity to diffuse fraction exhibited by corn and alfalfa crops. We utilized an empirical model to assess the trade‐off between enhanced diffuse fraction and reduced total PAR. Under mean radiation conditions, daily integrated gross ecosystem productivity increased by 1.2–4.2% compared to the previous growing season. Finally, we explore the potential negative effect of heightened ozone, a copollutant often associated with wildfire. In addition to the effects of wildfire smoke, the results of this natural experiment can help validate future predictions of aerosol‐productivity feedbacks.

Hemes, Kyle S.↗

Iron Speciation in PM 2.5 From Urban, Agriculture, and Mixed Environments in Colorado, USA

Atmospheric iron solubility varies depending on whether the particles are collected in rural or urban areas, with urban areas showing increased iron solubility. In this study, we investigate if the iron species present in different environments affects its ultimate solubility. Field data are presented from the Platte River Air Pollution and Photochemistry Experiment (PRAPPE), aimed at understanding the interactions between organic carbon and trace elements in atmospheric particulate matter (PM). 24-hr PM 2.5 samples were collected during the summer and winter (2016–2017), at three different sites on the Eastern Colorado plains: an urban, agricultural, and a mixed site. Downtown Denver had an average total and water-soluble iron air concentration of 181.2 and 7.7 ng m -3 , respectively. Platteville, the mixed site, had an average of total iron of 76.1 ng m -3 , with average water-soluble iron concentration of 9.1 ng m -3 . Jackson State Park (rural/agricultural) had the lowest total iron average of 31.5 ng m -3 and the lowest water-soluble iron average, 1.3 ng m -3 . The iron oxidation state and chemical speciation of 97 samples across all sites and seasons was probed by X-ray absorption near edge structure (XANES) spectroscopy. The most common iron phases observed were almandine (Fe 3 Al 2 Si 3 O 12 ) (Denver 21%, Platteville 16%, Jackson 24%), magnetite (Fe 3 O 4 ) (Denver 9%, Platteville 4%, Jackson 5%) and Fe (III)dextran (Denver 5%, Platteville 13%, Jackson 5%), a surrogate for Fe-organic complexes. Additionally, native iron [Fe(0)] was found in significant amounts at all sites. No correlation was observed between iron solubility and iron oxidation state or chemical speciation.

54 ENVIRONMENTAL SCIENCES↗