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  • Wiley  (24)
  • Copernicus  (22)
  • Springer Nature  (13)
  • American Association for the Advancement of Science (AAAS)  (2)
  • 2020-2022  (8)
  • 2015-2019  (53)
  • 1
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    Oxidation of mercury by bromine in the subtropical Pacific free troposphere (2015)
    Wiley
    Details
    Publication Date: 2015-11-26
    Description: Mercury is a global toxin that can be introduced to ecosystems through atmospheric deposition. Mercury oxidation is thought to occur in the free troposphere by bromine radicals, but direct observational evidence for this process is currently unavailable. During the 2013 Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks (NOMADSS) campaign, we measured enhanced oxidized mercury and bromine monoxide in a free tropospheric air mass over Texas. We use trace gas measurements, air mass back-trajectories, and a chemical box model to confirm the origin and chemical history of the sampled air mass. We find the presence of elevated oxidized mercury to be consistent with oxidation of elemental mercury by bromine atoms in this subsiding upper tropospheric air mass within the subtropical Pacific High, where dry atmospheric conditions are conducive to oxidized mercury accumulation. Our results support the role of bromine as the dominant oxidant of mercury in the upper troposphere.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Measurements of Hydroxyl and Hydroperoxy Radicals during CalNex-LA: Model Comparisons and Radical Budgets (2016)
    Wiley
    Details
    Publication Date: 2016-04-03
    Description: Measurements of hydroxyl (OH) and hydroperoxy (HO 2 *) radical concentrations were made at the Pasadena ground site during the CalNex-LA 2010 campaign using the Laser-Induced Fluorescence - Fluorescence Assay by Gas Expansion (LIF-FAGE) technique. The measured concentrations of OH and HO 2 * exhibited a distinct weekend effect, with higher radical concentrations observed on the weekends corresponding to lower levels of nitrogen oxides (NO x ). The radical measurements were compared to results from a zero-dimensional model using the Regional Atmospheric Chemical Mechanism-2 (RACM2) constrained by NO x and other measured trace gases. The chemical model overpredicted measured OH concentrations during the weekends by a factor of approximately 1.4 ± 0.3 (1σ), but the agreement was better during the weekdays (ratio of 1.0 ± 0.2). Model predicted HO 2 * concentrations underpredicted by a factor of 1.3 ± 0.2 on the weekends, while measured weekday concentrations were underpredicted by a factor of 3.0 ± 0.5. However, increasing the modeled OH reactivity to match the measured total OH reactivity improved the overall agreement for both OH and HO 2 * on all days. A radical budget analysis suggests that photolysis of carbonyls and formaldehyde together accounted for approximately 40% of radical initiation with photolysis of nitrous acid accounting for 30% at the measurement height and ozone photolysis contributing less than 20%. An analysis of the ozone production sensitivity reveals that during the week, ozone production was limited by volatile organic compounds throughout the day during the campaign, but NO x -limited during the afternoon on the weekends.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Sustained Non‐Photochemical Quenching Shapes the Seasonal Pattern of Solar‐ Induced Fluorescence at a High‐Elevation Evergreen Forest (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Traditional methods of carbon monitoring in mountainous regions are challenged by complex terrain. Recently, solar‐induced fluorescence (SIF) has been found to be an indicator of gross primary production (GPP), and the increased availability of remotely‐sensed SIF provides an opportunity to estimate GPP across the Western US. Although the empirical linkage between SIF and GPP is strong, the current mechanistic understanding of this linkage is incomplete, and depends upon changes in leaf biochemical processes in which absorbed sunlight leads to photochemistry, heat (via non‐photochemical quenching, NPQ), fluorescence, or tissue damage. An improved mechanistic understanding is necessary to leverage SIF observations to improve representation of ecosystem processes within land surface models. Here, we included an improved fluorescence model within the Community Land Model, Version 4.5 (CLM 4.5) to simulate seasonal changes in SIF at a subalpine forest in Colorado. We found that when the model accounted for sustained NPQ this provided a larger seasonal change in fluorescence yield leading to simulated SIF that more closely resembled the observed seasonal pattern (GOME‐2 satellite platform and a tower‐mounted spectrometer system). We found that an acclimation model based on mean air temperature was a useful predictor for sustained NPQ. Although light intensity was not an important factor for this analysis, it should be considered before applying the sustained NPQ and SIF to other cold climate evergreen biomes. More leaf level fluorescence measurements are necessary to better understand the seasonal relationship between sustained and reversible components of NPQ and to what extent that influences solar‐induced fluorescence.
    Print ISSN: 2169-8953
    Electronic ISSN: 2169-8961
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Disentangling Changes in the Spectral Shape of Chlorophyll Fluorescence: Implications for Remote Sensing of Photosynthesis (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Novel satellite measurements of solar‐induced chlorophyll fluorescence (SIF) can improve our understanding of global photosynthesis; however, little is known about how to interpret the controls on its spectral variability. To address this, we disentangle simultaneous drivers of fluorescence spectra by coupling active and passive fluorescence measurements with photosynthesis. We show empirical and mechanistic evidence for where, why, and to what extent leaf fluorescence spectra change. Three distinct components explain more than 95% of the variance in leaf fluorescence spectra under both steady‐state and changing illumination conditions. A single spectral shape of fluorescence explains 84% of the variance across a wide range of species. The magnitude of this shape responds to absorbed light and photosynthetic up/down regulation; meanwhile, chlorophyll concentration and nonphotochemical quenching control 9% and 3% of the remaining spectral variance, respectively. The spectral shape of fluorescence is remarkably stable where most current satellite retrievals occur (“far‐red,” 〉740nm), and dynamic downregulation of photosynthesis reduces fluorescence magnitude similarly across the 670‐ to 850‐nm range. We conduct an exploratory analysis of hourly red and far‐red canopy SIF in soybean, which shows a subtle change in red:far‐red fluorescence coincident with photosynthetic downregulation but is overshadowed by longer‐term changes in canopy chlorophyll and structure. Based on our leaf and canopy analysis, caution should be taken when attributing large changes in the spectral shape of remotely sensed SIF to plant stress, particularly if data acquisition is temporally sparse. Ultimately, changes in SIF magnitude at wavelengths greater than 740 nm alone may prove sufficient for tracking photosynthetic dynamics.
    Print ISSN: 2169-8953
    Electronic ISSN: 2169-8961
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Low‐Frequency Induced Polarization of Porous Media Undergoing Freezing: Preliminary Observations and Modeling (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract We investigate the thermal dependence of the complex conductivity of nine porous materials in the temperature range +20 °C to −10 or −15 °C. The selected samples include three soils, two granites, three clay‐sands mixes, and one graphitic tight sandstone. A total of 12 experiments is conducted with one sample tested at three different salinities. Our goal is to use this database to extend the dynamic Stern layer polarization model in freezing conditions. We observe two polarization mechanisms, one associated with the effect of the change in the liquid water content and its salinity upon the polarization of the porous material. A second mechanism, at higher frequencies (〉10 Hz), is likely associated with the polarization of ice. At low frequencies and above the freezing point, the in‐phase and quadrature conductivities depend on temperature in a predictable way. This dependence is due to the dependence of the mobility of the charge carriers with temperature. Below the freezing point, the in‐phase and quadrature conductivity follow a brutal decay with temperature. This dependence is modeled through an exponential freezing curve function. We were also able to determine how the (apparent) formation factor and surface conductivity change with temperature and water content below the freezing point. Our model is able to replicate the data at low frequencies and predicts correctly the fact that the ratio between the normalized chargeability and the surface conductivity is independent of the water content and temperature and equals a well‐defined dimensionless number R.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Holocene small mammals hunted by owls and humans in southern Brazil: taphonomic evidence and biological significance (2019)
    Wiley
    In: Boreas
    Details
    Publication Date: 2019
    Description: Understanding resource utilization and economic diversification amongst Holocene hunter‐gatherers in southern Brazil requires in‐depth taphonomic analysis of faunal assemblages. Three Early to Late Holocene archaeological sites (Garivaldino, Pilger and Sangão) in Rio Grande do Sul State, southern Brazil, revealed large assemblages of small mammal (˂1 kg) remains, composed mainly of rodents. To appreciate depositional processes of fauna in relation to human consumption, taphonomic attributes and processes were evaluated. The results indicated that the remains accumulated through different antemortem taphonomic pathways, apparently linked to the size and natural history of the species represented. The small‐ and medium‐sized (〈150 g) cricetid rodents (e.g. Pseudoryzomys simplex and Sooretamys angouya) were represented by a low proportion of teeth with lightly digestive corrosion suggesting that they were derived from the predatory activity of owls, possibly Tyto alba. In contrast, large‐sized cricetids (〉150 g; Kunsia tomentosus, Gyldenstolpia sp. and Holochilus sp.), and several caviomorph rodents with aggregated spatial distributions (Echimyidae (†Dicolpomys fossor, Phyllomys sp., †Clyomys riograndensis and †Euryzygomatomys mordax), Caviidae (Cavia sp.) and Ctenomyidae (Ctenomys sp.)) showed evidence of thermoalteration patterns and cut marks on bones, suggesting human exploitation. A postmortem depositional environment was deduced from dendritic and branched patterns of rootlet etching, apparent mostly at Garivaldino and Pilger. Polished areas and holes on bone surfaces, and impregnation of manganese showed moderate (Sangão) or low (Garivaldino and Pilger) incidence, pointing to water transport under moderate (Pilger) and low (Garivaldino and Sangão) energy over short distances. The results obtained here provide the first clear evidence of early human exploitation of small mammals in southern Brazil, suggesting a diversification of economies. In addition, as several of the recorded rodents are today regionally or biologically extinct, a preliminary discussion about the potential impact of humans on this process is provided.
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
    Published by Wiley
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  • 7
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    Generation of a zebrafish SWATH-MS spectral library to quantify 10,000 proteins (2019)
    Springer Nature
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    Publication Date: 2019
    Electronic ISSN: 2052-4463
    Topics: Nature of Science, Research, Systems of Higher Education, Museum Science
    Published by Springer Nature
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  • 8
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    Evaluating N2O5 Heterogeneous Hydrolysis Parameterizations For CalNex 2010 (2016)
    Wiley
    Details
    Publication Date: 2016-04-24
    Description: Nighttime chemistry in the troposphere is closely tied to the dinitrogen pentoxide (N 2 O 5 ) budget, but high uncertainties remain regarding the model representation of the heterogeneous hydrolysis of N 2 O 5 on aerosol particles. In this study we used the community model WRF-Chem to simulate a three-day period during the California Nexus (CalNex) Campaign in 2010. We extended WRF-Chem to include the heterogeneous hydrolysis of N 2 O 5 and contrasted the impact of different published parameterizations of N 2 O 5 heterogeneous hydrolysis on the spatial distribution of uptake coefficients and the resulting N 2 O 5 concentrations. For all the cases, modeled N 2 O 5 uptake coefficients showed strong spatial variability, with higher values in the nocturnal boundary layer compared to the residual layer, especially in environments with high relative humidities, such as over the ocean and along the coast. The best agreement of modeled and observed uptake coefficients was obtained using the parameterization by Davis et al. [2008] combined with the treatment of organic coating by Riemer et al. [2009]. For this case the temporal evolution of lower boundary layer N 2 O 5 mixing ratios was reproduced well, and the predictions of surface mixing ratios of ozone and NO x were improved. However, the model still overpredicted the uptake coefficients in the residual layer and consequently underpredicted N 2 O 5 concentrations in the residual layer. This study also highlights that environments with low relative humidities pose a challenge for aerosol thermodynamic models in calculating aerosol water uptake, and this impacts N 2 O 5 heterogeneous hydrolysis parameterizations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Rapid cycling of reactive nitrogen in the marine boundary layer (2016)
    Springer Nature
    In: Nature
    Details
    Publication Date: 2016-04-28
    Description: Rapid cycling of reactive nitrogen in the marine boundary layer Nature 532, 7600 (2016). doi:10.1038/nature17195 Authors: Chunxiang Ye, Xianliang Zhou, Dennis Pu, Jochen Stutz, James Festa, Max Spolaor, Catalina Tsai, Christopher Cantrell, Roy L. Mauldin, Teresa Campos, Andrew Weinheimer, Rebecca S. Hornbrook, Eric C. Apel, Alex Guenther, Lisa Kaser, Bin Yuan, Thomas Karl, Julie Haggerty, Samuel Hall, Kirk Ullmann, James N. Smith, John Ortega & Christoph Knote Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A ‘renoxification’ process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth’s surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 10
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    ATMOSPHERIC SCIENCE. Comment on "Missing gas-phase source of HONO inferred from Zeppelin measurements in the troposphere" (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-06-20
    Description: Li et al. (Reports, 18 April 2014, p. 292) proposed a unity nitrous acid (HONO) yield for reaction between nitrogen dioxide and the hydroperoxyl-water complex and suggested a substantial overestimation in HONO photolysis contribution to hydroxyl radical budget. Based on airborne observations of all parameters in this chemical system, we have determined an upper-limit HONO yield of 0.03 for the reaction.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ye, Chunxiang -- Zhou, Xianliang -- Pu, Dennis -- Stutz, Jochen -- Festa, James -- Spolaor, Max -- Cantrell, Christopher -- Mauldin, Roy L -- Weinheimer, Andrew -- Haggerty, Julie -- New York, N.Y. -- Science. 2015 Jun 19;348(6241):1326. doi: 10.1126/science.aaa1992.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Wadsworth Center, New York State Department of Health, Albany, NY, USA. ; Wadsworth Center, New York State Department of Health, Albany, NY, USA. Department of Environmental Health Sciences, State University of New York, Albany, NY, USA. xianliang.zhou@health.ny.gov. ; Department of Environmental Health Sciences, State University of New York, Albany, NY, USA. ; University of California, Los Angeles, CA, USA. ; University of Colorado, Boulder, CO, USA. ; University of Colorado, Boulder, CO, USA. Department of Physics, University of Helsinki, Helsinki, Finland. ; National Center for Atmosphere Research, Earth System Laboratory, Boulder, CO, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26089507" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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