Methacrolein (MACR) is an abundant multifunctional carbonyl compound with highreactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiatedoxidation of MACR at various NO/MACR ratios (0 to 4.04) and relative humidities (< 3% to80%) using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanismwas performed to test our current understanding of the mechanism. In contrast to thereasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde(HCHO) were twice higher than the experimental results. The discrepancy was ascribed tothe existence of unconsidered non-HCHO forming channels in the chemistry of CH3C(=CH2)OO., which account for approx. 50%. In addition, the production of hydroxyacetoneand HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields ofHCHO were higher under humid conditions than that under dry condition. The yields ofhydroxyacetone were higher under humid conditions at low-NOx level, while lower athigh-NOx level. The reasonable explanation for the lower hydroxyacetone yield underhumid conditions at high-NOx level is that water vapor promotes the production ofmethacrolein nitrate in the reaction of HOCH2C(CH3)(OO.)CHO with NO due to the peroxyradical-water complex formation, which was evidenced by calculational results. And theminimum equilibrium constant of this water complex formation was estimated to be1.89 × 10−18 cm3/molecule. These results provide new insights into the MACR oxidationmechanismand the effects of water vapor.
The magmatic-hydrothermal evolution of porphyry-style mineralization in the shallow crust that is linked to magmatic processes at depth has been extensively studied using bulk-sample isotopic analysis combined with relative timing constraints. However, a lack of evaluation of the fluid evolution process against an absolute time frame limits further understanding of the ore-forming process. Here, we quantify the fluid evolution process within an absolute time frame for the first time by integrating new in situ oxygen isotope data from the Qulong porphyry Cu-Mo deposit (Tibet) with existing fluid inclusion data and high-precision Re-Os dates of co-precipitated hydrothermal quartz and molybdenite, respectively. We demonstrate that vein quartz records primary oxygen isotopic compositions and reached oxygen isotope equilibrium with ore-forming fluids, and therefore is an archive of the isotopic composition and source of the ore-forming fluids. The delta O-18(quartz) and delta O-18(fluid) values, in absolute time, show periodic fluctuations that indicate the presence of three intermittent pulses of magmatic fluid flux, which have been balanced by meteoric water. As such, the flux of magmatic fluid during ore formation was pulsed, rather than being continuous. The overall highest delta O-18(fluid) in the first pulse of mineralization, with a gradual decrease to the second and third pulses, is suggestive of a progressive reduction in the magmatic component of the hydrothermal fluids and, by inference, the mineralizing potential of the hydrothermal fluids. This view is supported by a decrease in sulfide-bearing fluid inclusions and metal grade through time. Our findings favor multiple fluid-release events from a single cooling magmatic reservoir, although multiple fluid-melt recharge events remain a competitive alternative. An additional implication is that the magmatic reservoir may have a lifespan of hundreds of thousands of years, with fluid release events occurring over tens of thousands of years.
Aircraft-based measurements of methane (CH4) and other air pollutants in the Athabasca Oil Sands Region (AOSR) were made during a summer intensive field campaign between 13 August and 7 September 2013 in support of the Joint Canada-Alberta Implementation Plan for Oil Sands Monitoring. Chemical signatures were used to identify CH4 sources from tailings ponds (BTEX VOCs), open pit surface mines (NOy and r BC) and elevated plumes from bitumen upgrading facilities (SO2 and NOy). Emission rates of CH4 were determined for the five primary surface mining facilities in the region using two mass-balance methods. Emission rates from source categories within each facility were estimated when plumes from the sources were spatially separable. Tailings ponds accounted for 45% of total CH4 emissions measured from the major surface mining facilities in the region, while emissions from operations in the open pit mines accounted for +/- 50 %. The average open pit surface mining emission rates ranged from 1.2 to 2.8 t of CH4 h(-1) for different facilities in the AOSR. Amongst the 19 tailings ponds, Mildred Lake Settling Basin, the oldest pond in the region, was found to be responsible for the majority of tailings ponds emissions of CH4 (> 70 %). The sum of measured emission rates of CH4 from the five major facilities, 19.2 +/- 1.1 tCH(4) h(-1), was similar to a single mass-balance determination of CH4 from all major sources in the AOSR determined from a single flight downwind of the facilities, 23.7 +/- 3.7 tCH(4) h(-1). The measured hourly CH4 emission rate from all facilities in the AOSR is 48 +/- 8% higher than that extracted for 2013 from the Canadian Greenhouse Gas Reporting Program, a legislated facility-reported emissions inventory, converted to hourly units. The measured emissions correspond to an emissions rate of 0.17 +/- 0.01 TgCH(4) yr(-1) if the emissions are assumed as temporally constant, which is an uncertain assumption. The emission rates reported here are relevant for the summer season. In the future, effort should be devoted to measurements in different seasons to further our understanding of the seasonal parameters impacting fugitive emissions of CH4 and to allow for better estimates of annual emissions and year-to-year variability.
We study the effects of infrared radiation on a two-dimensional Bardeen–Cooper–Schrieffer superconductor coupled with a normal metal substrate through a tunneling barrier. The phase transition is analyzed by inspecting the stability of the system against perturbations of pairing potentials. We find an oscillating gap phase with a frequency not directly related to the radiation frequency, but instead resulting from the asymmetry of electron density of states of the system as well as the tunneling amplitude. When such a superconductor is in contact with another superconductor, gives rise to an unusual alternating Josephson current .
The North China Plain has been identified as a significant hotspot of ammonia (NH3) due to extensive agricultural activities. Satellite observations suggest a significant increase of about 30% in tropospheric gas-phase NH3 concentrations in this area during 2008-2016. However, the estimated NH3 emissions decreased slightly by 7% because of changes in Chinese agricultural practices, i.e., the transition in fertilizer types from ammonium carbonate fertilizer to urea, and in the livestock rearing system from free-range to intensive farming. We note that the emissions of sulfur dioxide (SO2) have rapidly declined by about 60% over the recent few years. By integrating measurements from ground and satellite, a long-term anthropogenic NH3 emission inventory, and chemical transport model simulations, we find that this large SO2 emission reduction is responsible for the NH3 increase over the North China Plain. The simulations for the period 2008-2016 demonstrate that the annual average sulfate concentrations decreased by about 50 %, which significantly weakens the formation of ammonium sulfate and in- creases the average proportions of gas-phase NH3 within the total NH3 column concentrations from 26% (2008) to 37% (2016). By fixing SO2 emissions of 2008 in those multi-year simulations, the increasing trend of the tropospheric NH3 concentrations is not observed. Both the decreases in sulfate and increases in NH3 concentrations show highest values in summer, possibly because the formation of sulfate aerosols is more sensitive to SO2 emission reductions in summer than in other seasons. Besides, the changes in NOx emissions and meteorological conditions both decreased the NH3 column concentrations by about 3% in the study period. Our simulations suggest that the moderate reduction in NOx emissions (16 %) favors the formation of particulate nitrate by elevating ozone concentrations in the lower troposphere.
Economic, policy, and climate changes have profoundly influenced pastoral social-ecological systems on the Tibetan Plateau. Climate change is believed to be leading to increasing extreme weather conditions such as snow disasters and droughts, putting a strain on the rangeland resources herders must have to increase income. Market-based economic reforms and interrelated development policies such as the Rangeland Household Contract Policy, the Ecological Construction Project, and herder settlement Initiatives have increased integration of pastoral regions into modern markets with promotion of tourism, expanded livestock markets, and marketing opportunities for rangeland resources. Although allocating common rangelands to households is the foundation of current rangeland management strategies to achieve these goals, it removes important technologies for coping with high variability in rangeland forage production from the traditional rangeland management portfolio on the Tibetan Plateau. These include shared risk, shared labor, seasonal and yearly herd mobility, and access to diverse areas of rangelands and multiple water sources. Field study of two villages in Guinan County of Qinghai Province, and Ruoergai County of Sichuan Province from 2011 to 2014 found that the villages responded to externally driven policy, economic, and climate changes with an innovative locally adapted quota-based grazing management system that preserves valuable management technologies, conserves rangeland resources, and provides individual opportunities for financial gain. In this way the village social-ecological system has exhibited considerable resiliency, maintaining a form of community governance that functions to manage the rangelands, improve well-being as indicated by livestock productivity, and, according to local perceptions, maintain rangeland condition. The community-based grazing quota system devised by the villages occupies a middle ground between common and individual models for resource use because it focuses more on how to equitably distribute services and utilities from rangelands, instead of how to distribute rangelands.
Organic-inorganic hybrid perovskite solar cells (SCs) have emerged as one of the most promising contenders to traditional silicon solar cells, due to their active layers outstanding photoelectric properties, such as appropriate direct bandgap, balanced high carrier mobility and long carrier diffusion length, the identified power conversion efficiency (PCE) has reached to 22.7%. But the toxic lead, a key component in the archetypical light harvesting material, is a large obstacle to commercialization. Herein, we reviewed the recent progress in lead-free perovskite (-like) SCs according to the valent difference of metal ions in absorber material, e.g., bivalent (Sn2+, Ge2+, Cu2+, Sr2+), trivalent (Bi3+, Sb3+), tetravalent (Sn4+) and hybrid valent (e.g. Ag+ and Bi3+). Finally, we gave an outlook on the tactic to achieve high performance lead-free perovskite (-like) SCs. (c) 2018 Elsevier Ltd. All rights reserved.