Britt A. Holmén

Hydroxamate ligands, surface chemistry, and the mechanism of ligand-promoted dissolution of goethite [α-FeOOH(s)]

The rate of goethite dissolution in the presence of acetohydroxamic acid, chosen to be representative of hydroxamate siderophores, was examined in order to understand the cycling of iron in soils. The surface chemistry is surprisingly complicated, with dissolution at pH 4, the rate of dissolution is dominated by the ligand-induced reaction and we propose a mechanism where the rate-controlling step involves replacement of the oxygens near the detaching Fe(III)-monohydroxamate surface complex with water molecules. The adsorbate stoichiometry is given by reaction of oxime and adjacent carbonyl functional groups on the ligand with paired -OH 2 and -OH functional groups at monoatomic steps on the goethite surface. Potential factors influencing the rate of iron oxide dissolution by the higher molecular weight siderophores that are produced by iron-deficient microbes include hydrophobic bonding and possible chelation to several Fe(III) sites at the mineral surface.

Soy biodiesel and petrodiesel emissions differ in size, chemical composition and stimulation of inflammatory responses in cells and animals.

Debate about the biological effects of biodiesel exhaust emissions exists due to variation in methods of exhaust generation and biological models used to assess responses. Because studies in cells do not necessarily reflect the integrated response of a whole animal, experiments were conducted in two human cell lines representing bronchial epithelial cells and macrophages and female mice using identical particle suspensions of raw exhaust generated by a Volkswagen light-duty diesel engine using petrodiesel (B0) and a biodiesel blend (B20: 20% soy biodiesel/80% B0 by volume). Tailpipe particle emissions measurement showed B0 generated two times more particle mass, larger ultrafine particle number distribution modes, and particles of more nonpolar organic composition than the B20 fuel. Biological assays (inflammatory mediators, oxidative stress biomarkers) demonstrated that particulate matter (PM) generated by combustion of the two fuels induced different responses in in vitro and in vivo models. Concentrations of inflammatory mediators (Interleukin-6, IL-6; Interferon-gamma-induced Protein 10, IP-10; Granulocyte-stimulating factor, G-CSF) in the medium of B20-treated cells and in bronchoalveolar lavage fluid of mice exposed to B20 were ∼20-30% higher than control or B0 PM, suggesting that addition of biodiesel to diesel fuels will reduce PM emissions but not necessarily adverse health outcomes.

Design, Fabrication, and Testing of a Microfabricated Corona Ionizer

A microfabricated corona ionizer is developed for miniaturized air particle monitoring instruments. Peeks breakdown criterion and Warburgs Law are used to calculate the required electrode geometries. Single mask electroplating is employed as the microfabrication technique. Devices with discharge pin radius of 20 mum and interelectrode spacing of 1.4, 1.8, 2.0, and 2.2 mm are fabricated and tested. The inception voltages in the range from 1.4 to 2 kV are achieved without substrate breakdown. It consumes relatively low power at 150 mW or less. Corona charging currents of more than 50 muA were achieved before streamers break down. The experimental results also demonstrated the nondependency of the inception voltage on the pins radius of curvature so long as it is significantly smaller than the interelectrode spacing. There is only one value of inception voltage for each given interelectrode spacing (1.4 to 2.2 mm) with the pins radius of curvature ranging from 10 to 200 mum. This implies that strict dimensional control is not required in the microfabrication process in order to ensure the same inception voltage for each device.

Electrical Mobility Separation of Airborne Particles Using Integrated Microfabricated Corona Ionizer and Separator Electrodes

Airborne particles are separated according to their electrical mobilities using a microfabricated corona ionizer and separator electrodes. Oleic acid particles with sizes ranging from 30 to 300 nm are used to characterize the device. They are generated using a TSI 3075 constant output atomizer. These particles are electrically charged by a microfabricated corona ionizer, and the resultant particle electrical mobility is a function of the size of the particle. A varying DC potential difference of 0-2 kV across the separator electrodes selects charged particles of various electrical mobilities. These separated particles are subsequently counted using a TSI 3025A condensation particle counter. The device demonstrated its ability to separate particles between 50 and 130 nm into five distinct size bins. The operational flow rate is 0.5 L/min, and the micropin-between-planes corona ionizer operates at 1.3 kV with 7 muA. The theoretical and experimental electrical mobilities of the particles are compared.

Hydroxamate siderophores, cell growth and Fe(III) cycling in two anaerobic iron oxide media containing Geobacter metallireducens

Abstract We test the hypothesis that a versatile strain of iron bacteria, Geobacter metallireducens, can metabolize Fe(III) when it is complexed to hydroxamate ligands. Pure cultures were grown under anaerobic conditions with, and without, a Fe(III)(tris)acetohydroxamic acid complex as a source of Fe(III). These experiments were conducted with goethite [α-FeOOH] and amorphous iron hydroxide [Fe(OH)3(s)] to determine whether hydroxamate ligands can stimulate cell growth by dissolving Fe(III) from the mineral surface. We found that solids reduced the bacterial activity by lowering dissolved Fe(III) concentrations relative to solid-free medium. Acetohydroxamate did not significantly enhance cell growth, possibly because the Fe(III) was too difficult to reduce when complexed in a trihydroxamate complex. The hydroxamate ligand also had a dramatic effect on the cell morphology, such cell numbers could be used as a measure of microbial activity in solutions with this ligand, and there is evidence for an abiotic pathway for Fe(II) oxidation in the media containing hydroxamate.

Collection of Liquid Phase Particles by Microfabricated Electrostatic Precipitator

A microfabricated electrostatic precipitator successfully demonstrated its airborne liquid phase particles precipitation functionality. The particles used in the experiments were polydispersed liquid phase oleic acid particles with sizes ranging from 30 nm to 300 nm. Two configurations with electrode gaps of 1.8 mm and 2.0 mm were tested at 2.2 kV and 2.6kV, respectively. During the test, the microfabricated electrostatic precipitator was inserted into a flow chamber with an aerosol stream containing oleic acid particles. Particle precipitation is demonstrated via both visual observation and the measurement of the corona current during aerosol exposure. The corona current for the 2.0 mm electrode gap configuration was decreased by approximately 50% and the circuit resistivity is increased by the corresponding magnitude as the oleic acid particles precipitated during a 60s exposure. The recovery of corona current is observed when the aerosol source is turned off. Wicking of precipitated oleic acid away from the collection grid to its anchoring feature is observed. The analytical and experimental corona current versus time elapsed during the aerosol exposure are calculated and compared. The discrepancy between the analytical and experimental corona currents is consistent with the observed wicking effect and variation in percent coverage on the collector grid by precipitating particles.

Local dust emission factors for agricultural tilling operations.

Dust emission factors for regional- and local-scale simulations of particulate matter with diameters less than or equal to 10 &mgr;m (PM10) dispersion from agricultural operations are not generally available. This article presents a modification of the U.S. Environmental Protection Agency AP-42 approach to better calculate aerosol emission factors of PM10 for agricultural tilling operations. For the modification, we added the variables soil moisture, operation type, and crop type based on experimental and literature data to estimate local emission factors. Field experiments to measure the PM10 emissions from rolling, disking, listing, planting, and harvesting cotton (Gossypium hirsutum L.) were conducted. Data from these field experiments plus literature data were used to isolate the effects of soil moisture and operation type on the emissions. Literature data were then used to add different crop and operation types.

Particle Number and Size Distribution of Emissions During Light-Duty Vehicle Cold Start: Data from the Total Onboard Tailpipe Emissions Measurement System

Vehicle emissions during cold start are known to be significantly higher than after optimal vehicle operating temperatures are reached. There are limited data, however, on particle number and size distributions during cold start. Cold-start tailpipe emissions from a 1999 Toyota Sienna minivan were quantified at ambient temperatures between 20°C and 37°C using a novel system, the total onboard tailpipe emissions measurement system (TOTEMS), assembled to quantify the full suite of exhaust emissions from light-duty vehicles. TOTEMS particle number distributions were measured from 5.6 to 562 nm using an engine exhaust particle sizer (EEPS) and total 3- to 3,000-nm particle counts were measured using an ultrafine condensation particle counter (UCPC) with 1-s temporal resolution during cold start and warm-up driving. Second-by-second particle number distributions from five cold-start emissions tests showed similar particle emissions patterns, allowing for three different cold-start phases to be identified based on particle number emissions behavior. Cold-start duration ranged from 165 to 230 s and increased with decreasing ambient temperature. Different particle sizes during each phase were emitted for different lengths of time, with the most abundant particles in the nanoparticle (diameter <50 nm) range. The mean particle number distributions showed more than 99% of total particle number below 100 nm. Concentrations of ultrafine particles (<100 nm) during cold start were at least 10 to 100 times (EEPS), and as much as 1,000 times (UCPC), above hot-stabilized idle emissions. Observations also suggest the presence of tiny particles below 6 nm during cold start.

Modal Analysis of Vehicle Operation and Particulate Emissions from Connecticut Transit Buses

Transit buses represent a significant source of particulate exhaust emissions, especially in urban areas, but few previous studies have quantified these emissions by using real-world, onboard sampling while the vehicles operate in the transportation network. In this study, real-world particle number emissions for hybrid diesel–electric (HDE) and conventional diesel (CD) buses are examined for various vehicle operating conditions and road types in the Hartford, Connecticut, region. The results presented in this paper are based on analysis of the unique second-by-second Connecticut Transit on-road transit bus emissions and operations data set collected between January and November 2004. The modal analysis results indicate that hybrid buses operate differently than do conventional diesel buses. Although the distributions of vehicle specific power (VSP) values (in kw) were similar for the two bus types, the distributions of engine operation parameters (load and speed) were different. More important, VSP alone cannot be used to distinguish between vehicle types for modeling engine operation of, and possibly emissions from hybrid and conventional vehicles. Furthermore, modal analysis of ultrafine particle emissions indicates that in some situations the HDE buses do not outperform the CDs and may even produce higher emission rates than do the CD buses tested. Thus, there are routes and conditions in which transit authorities should avoid the use of HDE buses similar to those tested here when particle emissions are of concern. The observed high particle emissions on steep uphill grades for hybrids indicate that careful route selection for hybrid buses is warranted to optimize the environmental benefits of the hybrid vehicles.

Second-by-Second Characterization of Cold-Start Gas-Phase and Air Toxic Emissions from a Light-Duty Vehicle

Tailpipe pollutants from motor vehicles are linked to environmental concerns and human health issues. Gasoline engine ignition produces a significant portion of trip emissions, but few studies have quantified mobile source air toxic (MSAT) species for light-duty vehicles during cold start. Real-world tailpipe emissions were measured from a 1999 Toyota Sienna minivan with the University of Vermont total onboard tailpipe emissions measurement system. A Fourier transform infrared spectrometer measured 27 gas-phase emissions for cold start, extended idle, and warm-up driving at 1-s temporal resolution. Analysis demonstrated that (a) time to optimal function of emissions control devices was not indicated by one species, but varied for different pollutants; (b) extended idling after cold start produced elevated emissions for MSAT species as compared to warm-up driving; and (c) ambient temperatures ranging from 9.5°C to 38.4°C affected species from each emission category, with the exception of carbon dioxide. Carbon monoxide produced peak emissions three orders of magnitude higher than hot-stabilized conditions for an average of 90 s, regardless of operating conditions, while nitric oxide peak emissions were over an order of magnitude higher during warm-up driving than extended idle. Peak MSAT emissions, up to two orders of magnitude higher than hot-stabilized idle, were maintained or increased during extended idle and decreased to baseline within 100 to 200 s of warm-up driving. Results indicate extended idling after cold starts prolongs elevated concentrations of MSAT emissions, suggesting that recent policy efforts to reduce vehicle idling behavior could limit potential human exposure to the toxic exhaust constituents.