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Author(s): Jiangyi Zhang [sup.1] [sup.2] , Zhifang Xu [sup.1] [sup.2] Author Affiliations: (1) grid.458476.c, 0000 0004 0605 1722, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, [...], The accurate determination of arsenic species in waters is still an environmental challenge because of the rapid redox transformation of As. So, a procedure for on-site separation of As(III), As(V), methylarsonic acid, and dimethylarsinic acid in natural waters has been developed. The procedure involves passing a water sample through tandem cation- and anion-exchange resin columns in the field. Selective retention of arsenic species occurs in resin cartridges followed by selective elution. The eluate is collected and analyzed by inductively coupled plasma mass spectrometry. The standard reference material CASS-5 was diluted 10 times and analyzed directly to validate accuracy of measurements, and SLRS-2 was used to validate on-site separation procedure, respectively. The results agreed well with the certified values of standard reference materials. The proposed procedure was applied to the on-site separation of arsenic species from natural waters.

Author(s): Jiangyi Zhang [sup.1] [sup.2] , Zhifang Xu [sup.1] [sup.2] Author Affiliations: (1) grid.458476.c, 0000 0004 0605 1722, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, [...], Direct determination of dissolved silicon (DSi) in atmospheric precipitation by ICP-MS is still a challenge because of the presence of serious mass interferences. In this work, a reliable method based on CH.sub.4-Ar mixed gas plasma DRC-ICP-MS was successfully used for the direct determination of DSi in atmospheric precipitation samples. The interfering ions (.sup.14N.sup.14N.sup.+, .sup.12C.sup.16O.sup.+) were directly removed by the reaction with carbon dioxide gas and could be reduced by up to 99% at m/z 28. In addition, the sensitivity of .sup.28Si.sup.+ was 2-fold improved by CH.sub.4 modifier that was introduced to the ICP plasma at 2 mL/min, and the background signal was decreased to 60%. Under the optimized conditions, the limit of quantification was 5 [mu]g/L, and the reproducibility (RSD) was generally less than 3%. The proposed method was assessed using surface water standard reference materials, and the measured values agreed well with the certified values.

We study the propagation rules of acoustic bright solitons in bubble-containing media, as well as the strong anti-interference ability of acoustic solitons; and the effects of nonlinearity, dispersion, and dissipation on the dynamic properties of acoustic solitons are also analyzed. Based on the bubble–liquid mixture model, a lossy nonlinear Schrödinger equation is obtained. The analytical expression of the enveloped bright-acoustic solitons in the bubbly liquids is derived, which can accurately capture the propagation law of the acoustic bright solitons in the physical system, even if there is viscous loss in the medium. The dissipation-induced dynamics of acoustic solitons is studied through analytical and numerical methods, and the balancing effects of nonlinearity and dispersion in the propagation of bright solitons are analyzed. Furthermore, the particle nature and dynamic stability of bright-acoustic solitons in bubble-containing media are emphasized through fully elastic collisions between solitons moving in the same and opposite directions. This process obeys the energy and momentum conservation laws. After the collision, solitons can maintain their original amplitude, speed, and shape and continue to propagate undisturbed. [ABSTRACT FROM AUTHOR]

Ozone (O3), an important and ubiquitous trace gas, protects lives from harmful solar ultraviolet (UV) radiation in the stratosphere but is toxic to living organisms in the troposphere. Additionally, tropospheric O3 is a key oxidant and a source of other oxidants (e.g., OH and NO3 radicals) for various volatile organic compounds (VOCs). Recently, highly oxygenated organic molecules (HOM s) were identified as a new compound group formed from the oxidation of many VOCs, making up a significant source of secondary organic aerosol (SOA). The pathways forming HOM s from VOCs involve autoxidation of peroxy radicals (RO2), formed ubiquitously in many VOC oxidation reactions. The main sink for RO2 is bimolecular reactions with other radicals, such as HO2 , NO , or other RO2 , and this largely determines the structure of the end products. Organic nitrates form solely from RO2 + NO reactions, while accretion products ("dimers") form solely from RO2 + RO2 reactions. The RO2 + NO reaction also converts NO into NO2 , making it a net source for O3 through NO2 photolysis. There is a highly nonlinear relationship between O3 , NOx , and VOCs. Understanding the O3 formation sensitivity to changes in VOCs and NOx is crucial for making optimal mitigation policies to control O3 concentrations. However, determining the specific O3 formation regimes (either VOC-limited or NOx -limited) remains challenging in diverse environmental conditions. In this work we assessed whether HOM measurements can function as a real-time indicator for the O3 formation sensitivity based on the hypothesis that HOM compositions can describe the relative importance of NO as a terminator for RO2. Given the fast formation and short lifetimes of low-volatility HOMs (timescale of minutes), they describe the instantaneous chemical regime of the atmosphere. In this work, we conducted a series of monoterpene oxidation experiments in our chamber while varying the concentrations of NOx and VOCs under different NO2 photolysis rates. We also measured the relative concentrations of HOMs of different types (dimers, nitrate-containing monomers, and non-nitrate monomers) and used ratios between these to estimate the O3 formation sensitivity. We find that for this simple system, the O3 sensitivity could be described very well based on the HOM measurements. Future work will focus on determining to what extent this approach can be applied in more complex atmospheric environments. Ambient measurements of HOMs have become increasingly common during the last decade, and therefore we expect that there are already a large number of groups with available data for testing this approach. [ABSTRACT FROM AUTHOR]

Particulate matter has major climate and health impacts, and it is therefore of utmost importance to be able to measure the composition of these particles to gain insights into their sources and characteristics. Many methods, both offline and online, have been employed over the years to achieve this goal. One of the most recent developments is the Vaporization Inlet for Aerosols (VIA) coupled to a nitrate Chemical Ionization Mass Spectrometer (NO 3 -CIMS), but a thorough understanding of the VIA–NO 3 -CIMS system remains incomplete. In this work, we ran a series of tests to assess the impacts from different systems and sampling parameters on the detection efficiency of highly oxygenated organic molecules (HOMs) in the VIA–NO 3 -CIMS system. Firstly, we found that the current VIA system (which includes an activated carbon denuder and a vaporization tube) efficiently transmits particles (> 90 % for particles larger than 50 nm) while also removing gaseous compounds (> 97% for tested volatile organic compounds – VOCs). One of the main differences between the VIA and traditional thermal desorption (TD) techniques is the very short residence time in the heating region, on the order of 0.1 s. We found that this short residence time, and the corresponding short contact with heated surfaces, is likely one of the main reasons why relatively reactive or weakly bound peroxides, for example, were observable using the VIA. However, the VIA also requires much higher temperatures in order to fully evaporate the aerosol components. For example, the evaporation temperature of ammonium sulfate particles using the VIA was found to be about 100–150 °C higher than in typical TD systems. We also observed that the evaporation of particles with larger sizes occurred at slightly higher temperatures compared to smaller particles. Another major aspect that we investigated was the gas-phase wall losses of evaporated molecules. With a more optimized interface between the VIA and the NO 3 -CIMS, we were able to greatly decrease wall losses and thus improve the sensitivity compared to our earlier VIA work. This interface included a dedicated sheath flow unit to cool the heated sample and provide the NO 3 -CIMS with the needed high flow (10 L min -1). Our results indicate that most organic molecules observable by the NO 3 -CIMS can evaporate and be transported efficiently in the VIA system, but upon contact with the hot walls of the VIA, the molecules are instantaneously lost. This loss potentially leads to fragmentation products that are not observable by the NO 3 -CIMS. Thermograms, obtained by scanning the VIA temperature, were found to be very valuable for both quantification purposes and for estimating the volatility of the evaporating compounds. We developed a simple one-dimensional model to account for the evaporation of particles and the temperature-dependent wall losses of the evaporated molecules, and we thereby estimate the concentration of HOMs in secondary organic aerosol (SOA) particles. Overall, our results provide much-needed insights into the key processes underlying the VIA–NO 3 -CIMS method. Although there are still some limitations that could be addressed through hardware improvements, the VIA–NO 3 -CIMS system is a very promising and useful system for fast online measurements of HOMs in the particle phase. [ABSTRACT FROM AUTHOR]

With the intensification of human activities, nitrate pollutants in groundwater are receiving increasing attention worldwide. Especially in the arid Nile Delta of Egypt, groundwater is one of the most valuable water resources in the region. Identifying the source of nitrate in groundwater with strong human disturbances is important to effective water resource management. This paper examined the stable isotopes (δ15N/δ18O-NO3 and δ2H/δ18O-H2O) and the hydrogeochemical parameters of the shallow groundwaters in the arid southeast of the Nile Delta to assess the potential sources and transformation processes of nitrate under severe urban and agricultural activities. The results revealed that the groundwaters were recharged by the Nile River. Meanwhile, the infiltration of irrigation water occurred in the west, while the mixing with the deep groundwater occurred in the east regions of the study area. The TDS, SO42−, NO3−, and Mn2+ concentrations of groundwaters (n = 55) exceeded the WHO permissible limit with 34.6%, 23.6%, 23.6%, and 65.5%, respectively. The NO3− concentrations in the shallow groundwaters ranged from 0.42 mg/L to 652 mg/L, and the higher levels were observed in the middle region of the study area where the unconfined condition prevailed. It extended to the deep groundwater and eastward of the study area in the groundwater flow direction. The δ15N-NO3 and δ18O-NO3 values suggested that the groundwater NO3− in the west and east regions of semi-confined condition were largely from the nitrification of soil organic nitrogen (SON) and chemical fertilizer (CF). In contrast, wastewater input (e.g., domestic sewage and unlined drains) and prevalent denitrification were identified in the middle region. The denitrification might be tightly coupled with the biogeochemical cycling of manganese. This study provides the first report on the groundwater NO3− dynamics in the Nile Delta, which generated valuable clues for effective water resource management in the arid region. [ABSTRACT FROM AUTHOR]

Ozone (O3), an important and ubiquitous trace gas, protects lives from harm of solar ultraviolet (UV) radiation in the stratosphere but is toxic to living organisms in the troposphere. Additionally, tropospheric O3 is a key oxidant, and source of other oxidants (e.g, OH and NO3 radicals) for various volatile organic compounds (VOC). Recently, highly oxygenated organic molecules (HOM) were identified as a new compound group formed from oxidation of many VOC, making up a significant source of secondary organic aerosol (SOA). The pathways forming HOM from VOC involve autoxidation of peroxy radicals (RO2), formed ubiquitously in many VOC oxidation reactions. The main sink for RO2 is bimolecular reactions with other radicals, HO2, NO or other RO2, and this largely determines the structure of the end products. Organic nitrates form solely from RO2 + NO reactions while accretion products ("dimers") solely from RO2 + RO2 reactions. The RO2 + NO reaction also converts NO into NO2, making it a net source for O3 through NO2 photolysis. There is a highly nonlinear relationship between O3, NOx, and VOC. Understanding the O3 formation sensitivity to changes in VOC and NOx is crucial for making optimal mitigation policies to control O3 concentrations. However, determining the specific O3 formation regimes (either VOC-limited or NOx-limited) remains challenging in diverse environmental conditions. In this work we assessed whether HOM measurements can function as a real-time indicator for the O3 formation sensitivity based on the hypothesis that HOM compositions can describe the relative importance of NO as a terminator for RO2. Given the fast formation and short lifetimes of the low-volatile HOM (timescale of minutes), they describe the instantaneous chemical regime of the atmosphere. In this work, we conducted a series of monoterpene oxidation experiments in our chamber while varying the concentrations of NOx and VOC under different NO2 photolysis rates. We also measured the relative concentrations of HOM of different types (dimers, nitrate-containing monomers, and non-nitrate monomers) and used ratios between these to estimate the O3 formation sensitivity. We find that for this simple system, the O3 sensitivity could be described very well based on the HOM measurements. Future work will focus on determining to what extent this approach can be applied in more complex atmospheric environments. Ambient measurements of HOM have become increasingly common during the last decade, and therefore we expect that there already are a large amount groups with available data for testing this approach. [ABSTRACT FROM AUTHOR]

In the past two decades, the research on acoustic metamaterials has flourished, which is also benefited from the development of additive manufacturing technology. The exotic physical phenomena and principles exhibited by acoustic metamaterials have attracted widespread attention from academia and engineering communities, which can be applied to noise reduction and acoustic nondestructive testing in industrial; invisible cloaking and camouflage in the military; medical ultrasound imaging in national health; acoustic stealth in defense security, detection in the ocean, communication, and other fields, i.e., acoustic metamaterials have important scientific research value and broad application prospects. This review summarizes the history and research status of acoustic metamaterials, focusing on the main research progress of metamaterials in nonlinear acoustic and acoustic coatings fields, including the research on acoustic coatings with cavities of our group. Finally, the future development direction of acoustic metamaterials is prospected, and the difficulties and challenges faced by the actual engineering of acoustic metamaterials are discussed, such as difficulties in mass production, hydrostatic pressure resistant property, omnidirectional wave control, high production costs, and so on. [ABSTRACT FROM AUTHOR]