Matching Items (44)

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Dissolved organic carbon (DOC) and select aldehydes in cloud and fog water: the role of the aqueous phase in impacting trace gas budgets

Description

Cloud and fog droplets efficiently scavenge and process water-soluble compounds and, thus, modify the chemical composition of the gas and particle phases. The concentrations of dissolved organic carbon (DOC) in

Cloud and fog droplets efficiently scavenge and process water-soluble compounds and, thus, modify the chemical composition of the gas and particle phases. The concentrations of dissolved organic carbon (DOC) in the aqueous phase reach concentrations on the order of ~ 10 mgC L[superscript −1] which is typically on the same order of magnitude as the sum of inorganic anions. Aldehydes and carboxylic acids typically comprise a large fraction of DOC because of their high solubility. The dissolution of species in the aqueous phase can lead to (i) the removal of species from the gas phase preventing their processing by gas phase reactions (e.g., photolysis of aldehydes) and (ii) the formation of unique products that do not have any efficient gas phase sources (e.g., dicarboxylic acids).
We present measurements of DOC and select aldehydes in fog water at high elevation and intercepted clouds at a biogenically-impacted location (Whistler, Canada) and in fog water in a more polluted area (Davis, CA). Concentrations of formaldehyde, glyoxal and methylglyoxal were in the micromolar range and comprised ≤ 2% each individually of the DOC. Comparison of the DOC and aldehyde concentrations to those at other locations shows good agreement and reveals highest levels for both in anthropogenically impacted regions. Based on this overview, we conclude that the fraction of organic carbon (dissolved and insoluble inclusions) in the aqueous phase of clouds or fogs, respectively, comprises 2–~ 40% of total organic carbon. Higher values are observed to be associated with aged air masses where organics are expected to be more highly oxidised and, thus, more soluble. Accordingly, the aqueous/gas partitioning ratio expressed here as an effective Henry's law constant for DOC (K[subscript H]*[superscript DOC]) increases by an order of magnitude from 7 × 10[superscript 3] M atm[superscript −1] to 7 × 10[superscript 4] M atm[superscript −1] during the ageing of air masses.
The measurements are accompanied by photochemical box model simulations. These simulations are used to contrast two scenarios, i.e., an anthropogenically vs. a more biogenically impacted one as being representative for Davis and Whistler, respectively. Since the simplicity of the box model prevents a fully quantitative prediction of the observed aldehyde concentrations, we rather use the model results to compare trends in aldehyde partitioning and ratios. They suggest that the scavenging of aldehydes by the aqueous phase can reduce HO[subscript 2] gas phase levels significantly by two orders of magnitude due to a weaker net source of HO[subscript 2] production from aldehyde photolysis in the gas phase. Despite the high solubility of dicarbonyl compounds (glyoxal, methylglyoxal), their impact on the HO[subscript 2] budget by scavenging is < 10% of that of formaldehyde. The overview of DOC and aldehyde measurements presented here reveals that clouds and fogs can be efficient sinks for organics, with increasing importance in aged air masses. Even though aldehydes, specifically formaldehyde, only comprise ~ 1% of DOC, their scavenging and processing in the aqueous phase might translate into significant effects in the oxidation capacity of the atmosphere.

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  • 2013-05-21

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Physical–chemical characterisation of the particulate matter inside two road tunnels in the São Paulo Metropolitan Area

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The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in

The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in particulate matter vehicular emission profiles. In an effort to better characterise the emitted particulate matter, measurements of aerosol physical and chemical properties were undertaken inside two tunnels located in the São Paulo Metropolitan Area (SPMA). The tunnels show very distinct fleet profiles: in the Jânio Quadros (JQ) tunnel, the vast majority of the circulating fleet are light duty vehicles (LDVs), fuelled on average with the same amount of ethanol as gasoline. In the Rodoanel (RA) tunnel, the particulate emission is dominated by heavy duty vehicles (HDVs) fuelled with diesel (5% biodiesel). In the JQ tunnel, PM[subscript 2.5] concentration was on average 52 μg m[superscript −3], with the largest contribution of organic mass (OM, 42%), followed by elemental carbon (EC, 17%) and crustal elements (13%). Sulphate accounted for 7% of PM[subscript 2.5] and the sum of other trace elements was 10%. In the RA tunnel, PM[subscript 2.5] was on average 233 μg m[superscript −3], mostly composed of EC (52%) and OM (39%). Sulphate, crustal and the trace elements showed a minor contribution with 5%, 1%, and 1%, respectively. The average OC : EC ratio in the JQ tunnel was 1.59 ± 0.09, indicating an important contribution of EC despite the high ethanol fraction in the fuel composition. In the RA tunnel, the OC : EC ratio was 0.49 ± 0.12, consistent with previous measurements of diesel-fuelled HDVs. Besides bulk carbonaceous aerosol measurement, polycyclic aromatic hydrocarbons (PAHs) were quantified. The sum of the PAHs concentration was 56 ± 5 ng m[superscript −3] and 45 ± 9 ng m[superscript −3] in the RA and JQ tunnel, respectively. In the JQ tunnel, benzo(a)pyrene (BaP) ranged from 0.9 to 6.7 ng m[superscript −3] (0.02–0.1‰ of PM[subscript 2.5)] whereas in the RA tunnel BaP ranged from 0.9 to 4.9 ng m[superscript −3] (0.004–0. 02‰ of PM[subscript 2.5]), indicating an important relative contribution of LDVs emission to atmospheric BaP.

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  • 2013-12-17

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Black carbon concentrations and sources in the marine boundary layer of the tropical Atlantic Ocean using four methodologies

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Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a

Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a high concentration of aerosols, such as black carbon, due to the African emission plume of biomass and agricultural burning products. Atmospheric particulate matter samples across the tropical Atlantic boundary layer were collected in the summer of 2010 during the southern hemispheric dry season when open fire events were frequent in Africa and South America. The highest black carbon concentrations were detected in the Caribbean Sea and within the African plume, with a regional average of 0.6 μg m[superscript −3] for both. The lowest average concentrations were measured off the coast of South America at 0.2 to 0.3 μg m[superscript −3]. Samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols (i.e., thermally unstable organic carbon, soot like, and charcoal like). Soot-like aerosols composed up to 45% of the carbonaceous aerosols in the Caribbean Sea to as little as 4% within the African plume. Charcoal-like aerosols composed up to 29% of the carbonaceous aerosols over the oligotrophic Sargasso Sea, suggesting that non-soot-like particles could be present in significant concentrations in remote environments. To better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions.

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  • 2014-07-18

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Organic composition and source apportionment of fine aerosol at Monterrey, Mexico, based on organic markers

Description

Primary emissions from anthropogenic and biogenic sources as well as secondary formation are responsible for the pollution levels of ambient air in major urban areas. These sources release fine particles

Primary emissions from anthropogenic and biogenic sources as well as secondary formation are responsible for the pollution levels of ambient air in major urban areas. These sources release fine particles into the air that negatively impact human health and the environment. Organic molecular markers, which are compounds that are unique to specific PM[subscript 2.5] sources, can be utilized to identify the major emission sources in urban areas. In this study, 43 representative PM[subscript 2.5] samples, for both daytime and nighttime periods, were built from individual samples collected in an urban site of the Monterrey metropolitan area (MMA) during the spring and fall of 2011 and 2012. The samples were analyzed for organic carbon, elemental carbon, and organic molecular markers. Several diagnostic tools were employed for the preliminary identification of emission sources. Organic compounds for eight compound classes were quantified. The n-alkanoic acids were the most abundant, followed by n-alkanes, wood smoke markers, and levoglucosan/alkenoic acids. Polycyclic aromatic hydrocarbons (PAHs) and hopanes were less abundant. The carbon preference index (0.7–2.6) for n-alkanes indicates a major contribution of anthropogenic and mixed sources during the fall and the spring, respectively. Hopanes levels confirmed the contribution from gasoline and diesel engines. In addition, the contribution of gasoline and diesel vehicle exhaust was confirmed and identified by the PAH concentrations in PM[subscript 2.5]. Diagnostic ratios of PAHs showed emissions from burning coal, wood, biomass, and other fossil fuels. The total PAHs and elemental carbon were correlated (r[superscript 2] =  0.39–0.70) across the monitoring periods, reinforcing that motor vehicles are the major contributors of PAHs. Cholesterol levels remained constant during the spring and fall, showing evidence of the contribution of meat-cooking operations, while the isolated concentrations of levoglucosan suggested occasional biomass burning events. Finally, source attribution results obtained using the CMB (chemical mass balance) model indicate that emissions from motor vehicle exhausts are the most important, accounting for the 64 % of the PM[subscript 2.5], followed by meat-cooking operations with 31 % The vegetative detritus and biomass burning had the smallest contribution (2.2 % of the PM[subscript 2.5]). To our knowledge, this is only the second study to explore the organic composition and source apportionment of fine organic aerosol based on molecular markers in Mexico and the first for the MMA. Particularly molecular marker were quantified by solvent extraction with dichloromethane, derivatization, and gas chromatography with mass spectrometry (GC/MS).

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  • 2016-01-26

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Chemical characterization of organic particulate matter from on-road traffic in Sao Paulo, Brazil

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This study reports emission of organic particulate matter by light-duty vehicles (LDVs) and heavy-duty vehicles (HDVs) in the city of São Paulo, Brazil, where vehicles run on three different fuel

This study reports emission of organic particulate matter by light-duty vehicles (LDVs) and heavy-duty vehicles (HDVs) in the city of São Paulo, Brazil, where vehicles run on three different fuel types: gasoline with 25 % ethanol (called gasohol, E25), hydrated ethanol (E100), and diesel (with 5 % biodiesel). The experiments were performed at two tunnels: Jânio Quadros (TJQ), where 99 % of the vehicles are LDVs, and RodoAnel Mário Covas (TRA), where up to 30 % of the fleet are HDVs. Fine particulate matter (PM[subscript 2.5]) samples were collected on quartz filters in May and July 2011 at TJQ and TRA, respectively. The samples were analyzed by thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and by thermal–optical transmittance (TOT). Emission factors (EFs) for organic aerosol (OA) and organic carbon (OC) were calculated for the HDV and the LDV fleet. We found that HDVs emitted more PM[subscript 2.5] than LDVs, with OC EFs of 108 and 523 mg kg[superscript −1] burned fuel for LDVs and HDVs, respectively. More than 700 ions were identified by TD-PTR-MS and the EF profiles obtained from HDVs and LDVs exhibited distinct features. Unique organic tracers for gasoline, biodiesel, and tire wear have been tentatively identified. nitrogen-containing compounds contributed around 20 % to the EF values for both types of vehicles, possibly associated with incomplete fuel burning or fast secondary production. Additionally, 70 and 65 % of the emitted mass (i.e. the OA) originates from oxygenated compounds from LDVs and HDVs, respectively. This may be a consequence of the high oxygen content of the fuel. On the other hand, additional oxygenation may occur during fuel combustion. The high fractions of nitrogen- and oxygen-containing compounds show that chemical processing close to the engine / tailpipe region is an important factor influencing primary OA emission. The thermal-desorption analysis showed that HDVs emitted compounds with higher volatility, and with mainly oxygenated and longer chain hydrocarbons than LDVs.

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  • 2016-11-18

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SILVER NANOPARTICLES: SYNTHESIS, SOLUBILITY, AND LEACHING OF COMMERCIAL PRODUCTS

Description

In recent years, products advertised to contain nanosilver have become increasingly popular; however, while companies often advertise for nanosilver products, little regulation occurs to verify that these products actually contain

In recent years, products advertised to contain nanosilver have become increasingly popular; however, while companies often advertise for nanosilver products, little regulation occurs to verify that these products actually contain silver nanoparticles. Furthermore, there currently exists much dispute regarding the safety and toxicity of silver nanoparticles. As more and more products incorporate nanosilver, the resolution of this dispute proves progressively important. The present study addressed these issues, with goals to synthesize silver nanoparticles, determine the solubility of the synthesized silver nanoparticles, and to evaluate leaching of nanosilver from commercially produced food storage containers. The silver nanoparticles were synthesized by a procedure devised by Leopold and Lendl, and subsequently evaluated for size and distribution by ICP-MS (Inductively Coupled Plasma Mass Spectrometry), SEC (Size Exclusion Chromatography), and DLS (Dynamic Light Scattering). The results indicated an average particle size of approximately 85 nm and a relatively monodispersed solution with a polydispersity value of 0.1245. The solubility of the nanoparticles was then examined using a dialysis experiment; however, the results of the dialysis experiments were inconclusive due to an aggregation that occurred which prevented the silver from diffusing out of the dialysis tubing. Lastly, commercially produced food storage containers advertised to contain silver nanoparticles were examined. These containers were digested using microwave assisted digestion, and subsequently analyzed using ICP-MS. It was determined that the containers contained between 7 .5 and 27 ug of silver per gram of container, and that the silver was not distributed uniformly throughout the container. While ICP-MS indicated the presence of silver, SEM (Scanning Electron Microscopy) failed to unambiguously identify silver nanoparticles in the container. The food storage containers were also examined for silver leaching under various conditions; it was found that the containers leached most greatly following exposure to an acidic solution and leached the least due to exposure to UV light. However, additional trials of the leaching experiments must be performed to validate the results obtained in these experiments.

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  • 2012-05

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Dating Deep-Sea Pelagic Clays with Osmium Isotopes to Reconstruct Sources of Iron to the South Pacific Gyre over 90 Million Years

Description

Iron (Fe) scarcity limits biological productivity in high-nutrient low-chlorophyll (HNLC) ocean regions. Thus, the input, output and abundance of Fe in seawater likely played a critical role in shaping the

Iron (Fe) scarcity limits biological productivity in high-nutrient low-chlorophyll (HNLC) ocean regions. Thus, the input, output and abundance of Fe in seawater likely played a critical role in shaping the development of modern marine ecosystems and perhaps even contributed to past changes in Earth’s climate. Three sources of Fe—wind-blown dust, hydrothermal activity, and sediment dissolution—carry distinct Fe isotopic fingerprints, and can therefore be used to track Fe source variability through time. However, establishing the timing of this source variability through Earth’s history remains challenging because the major depocenters for dissolved Fe in the ocean lack well-established chronologies. This is due to the fact that they are difficult to date with traditional techniques such as biostratigraphy and radiometric dating. Here, I develop age models for sediments collected from the International Drilling Program Expedition 329 by measuring the Os (osmium) isotopic composition of the hydrogenous portion of the clays. These extractions enable dating of the clays by aligning the Os isotope patterns observed in the clays to those in a reference curve with absolute age constraints through the Cenozoic. Our preliminary data enable future development of chronologies for three sediment cores from the high-latitude South Pacific and Southern Oceans, and demonstrate a wider utility of this method to establish age constraints on pelagic sediments worldwide. Moreover, the preliminary Os isotopic data provides a critical first step needed to examine the changes in Fe (iron) sources and cycling on millions of years timescales. Fe isotopic analysis was conducted at the same sites in the South Pacific and demonstrates that there are significant changes in the sources of Fe to the Southern Ocean over the last 90 Ma. These results lay the groundwork for the exploration of basin-scale sources to Fe source changes, which will have implications for understanding how biological productivity relates to Fe source variability over geological timescales.

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  • 2018-05

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Synthesis of Enzyme-Mimetic Catalysts

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The synthesis of the bis(2-diphenylphosphinoethyl)amine chelating ligand (1) was a crucial component in the preparation of non-canonical amino acids (NCAAs) throughout the project. Studies in this project indicated the need

The synthesis of the bis(2-diphenylphosphinoethyl)amine chelating ligand (1) was a crucial component in the preparation of non-canonical amino acids (NCAAs) throughout the project. Studies in this project indicated the need to isolate the ligand from its hydrochloride salt form seen in (1) which led to the synthesis of the brown oil, (Ph2PCH2CH2)2NH, (2). The ligand features a phosphine-nitrogen-phosphine group that is not observed in existing NCAAs. Phosphine groups are rarely seen in existing NCAAs and avoided by biochemists because they tend to oxidize before metal addition. In this project, (1) was used in a 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU) mediated method and palladium-catalyzed method to tether an amino acid to the nitrogen atom of the ligand framework. Both methods were monitored through the use of Nuclear Magnetic Resonance (NMR) spectroscopy. While the palladium catalyzed method exhibited little to no coupling, the 31P NMR spectrum obtained for the HATU mediated method did reveal that some coupling had occurred. The unsuccessful attempts to tether an amino acid to (1) led to the hypothesis that the phosphine groups were interfering with the palladium catalyst during the cross-coupling reaction. In an effort to test this hypothesis, (2) was reacted with the dimer, [Rh(nbd)Cl]2, to coordinate the rhodium metal to the free phosphorous arms and the nitrogen atom of the isolated PNP ligand. The PNP-based metal complex was used in the palladium catalyzed method, but cross-coupling was not observed. The new PNP-based metal complex was investigated to demonstrate that it exhibits moisture and air stability.

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  • 2018-05

Impact of Misting Systems on Local Air Quality

Description

-Please adjust the format of the abstract. m-3 should be typed as "m to the minus 3" with the "minus 3" in superscript
-see the additional "abstract.pdf" document for formatting

-Please adjust the format of the abstract. m-3 should be typed as "m to the minus 3" with the "minus 3" in superscript
-see the additional "abstract.pdf" document for formatting
In arid environments like Phoenix, many professional and residential outdoor spaces are cooled by the use of misting systems. These systems spray a fine mist of water droplets that cool down the surrounding air through the endothermic evaporation process. When the water droplets evaporate, they leave behind dissolved material that is present in the water, generating ambient particulate matter (PM). Thus, misting systems are a point source of PM. Currently there is no information on their impact on air quality in close proximity to these systems, or on the chemical composition of the particulate matter generated by the evaporating mist.
In this project, PM concentrations are found to increase on average by a factor of 8 from ambient levels in the vicinity of a residential misting system in controlled experiments. PM concentrations in public places that use misting systems are also investigated. The PM10 concentrations in public places ranged from 0.102 ± 0.010 mg m-3 to 1.47 ± 0.15 mg m-3, and PM2.5 ranged from 0.095 ± 0.010 mg m-3 to 0.99 ± 0.10 mg m-3. Air quality index (AQI) values based on these concentrations indicate that these levels of PM range from unhealthy to hazardous in most cases. PM concentrations tend to decrease after remaining relatively constant with increasing distance from misting systems. Chemical data reveal that chloride and magnesium ions may be used as tracers of aerosolized water from misting systems. The average chloride concentration was 71 µg m-3 in misting samples and below the detection limit for Cl- (< 8.2 µg m-3) in ambient samples. The average magnesium concentration was 11.7 µg m-3 in misting samples and 0.23 µg m-3 in ambient samples.

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  • 2020-05

Elemental composition of PM2.5 in Shiprock, New Mexico, a rural community located near coal-burning power plants and abandoned uranium mine tailings sites

Description

Fine particulate matter (PM[subscript 2.5]) was collected in Shiprock, New Mexico, a small community located near two coal–fired power plants and numerous abandoned uranium mine tailing sites. Eleven PM[subscript 2.5]

Fine particulate matter (PM[subscript 2.5]) was collected in Shiprock, New Mexico, a small community located near two coal–fired power plants and numerous abandoned uranium mine tailing sites. Eleven PM[subscript 2.5] samples were collected for 96 h over three sampling periods (April/May 2009, November 2009, and October/November, 2010). Nine samples were analyzed for 64 elements using inductively coupled plasma–mass spectrometry. B, Bi, Cu, Pb, Sb, Sn, and Zn were observed in at least eight samples at levels indicative of anthropogenic enrichment (enrichment factors between 30 and 650). All the seven elements could be explained by coal–combustion processes. B, Bi, and Sb are enriched in coals; Cu, Pb, Sn, and Zn are chalcophile–lithophile or chalcophile elements, all with appreciable affinity for sulfur, a component of coal. Principal component analysis also supported these findings. Four major sources (percent variance) were identified: soil (61%), coal combustion (17%), industrial (11%), and sea salt (5%). Concentrations of elements associated with coal combustion in Shiprock were lower than levels observed in other industrially influenced cities. This was explained by Shiprock’s location west of the power plants. Back trajectories indicated that winds arrive to Shiprock from the W, SW, and NW, but the power plants are located to the east (upwind) of the city. Samples were also analyzed for uranium (0.002–0.02 ng/m[superscript 3]) and other metals associated with mine tailings (Sr, Mo). All metals were detected but at low levels, and concentrations did not vary predictably with wind direction. Hence, the tailings sites could not be attributed as the source.

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  • 2014-07-01