Delhi, India, routinely experiences some of the world's highest urban
particulate matter concentrations. We established the Delhi Aerosol Supersite
study to provide long-term
characterization of the ...ambient submicron aerosol composition in Delhi. Here
we report on 1.25 years of highly time-resolved speciated submicron
particulate matter (PM1) data, including black carbon (BC) and
nonrefractory PM1 (NR-PM1), which we combine to develop a
composition-based estimate of PM1
(“C-PM1” = BC + NR-PM1) concentrations. We observed marked seasonal and diurnal variability in the concentration and
composition of PM1 owing to the interactions of sources and atmospheric
processes. Winter was the most polluted period of the year, with average
C-PM1 mass concentrations of ∼210 µg m−3. The monsoon was hot and rainy, consequently
making it the least polluted (C-PM1 ∼50 µg m−3) period. Organics constituted more than half
of the C-PM1 for all seasons and times of day. While ammonium, chloride,
and nitrate each were ∼10 % of the C-PM1 for the cooler
months, BC and sulfate contributed ∼5 % each. For the warmer
periods, the fractional contribution of BC and sulfate to C-PM1
increased, and the chloride contribution decreased to less than 2 %. The
seasonal and diurnal variation in absolute mass loadings were generally
consistent with changes in ventilation coefficients, with higher
concentrations for periods with unfavorable meteorology – low
planetary boundary layer height and low wind speeds. However, the variation
in C-PM1 composition was influenced by temporally varying sources,
photochemistry, and gas–particle partitioning. During cool periods when wind
was from the northwest, episodic hourly averaged chloride concentrations
reached 50–100 µg m−3, ranking
among the highest chloride concentrations reported anywhere in the world. We estimated the contribution of primary emissions and secondary processes to
Delhi's submicron aerosol. Secondary species contributed
almost 50 %–70 % of Delhi's C-PM1 mass for the
winter and spring months and up to 60 %–80 % for the warmer summer
and monsoon months. For the cooler months that had the highest C-PM1
concentrations, the nighttime sources were skewed towards primary sources,
while the daytime C-PM1 was dominated by secondary species. Overall,
these findings point to the important effects of both primary emissions and
more regional atmospheric chemistry on influencing the extreme particle
concentrations that impact the Delhi megacity region. Future air quality
strategies considering Delhi's situation in both a regional
and local context will be more effective than policies targeting only local,
primary air pollutants.
Chlorine-initiated oxidation of n-alkanes (C8−12) under high-nitrogen oxide conditions was investigated. Observed secondary organic aerosol yields (0.16 to 1.65) are higher than those for ...OH-initiated oxidation of C8−12 alkanes (0.04 to 0.35). A high-resolution time-of-flight chemical ionization mass spectrometer coupled to a Filter Inlet for Gases and AEROsols (FIGAERO–CIMS) was used to characterize the gas- and particle-phase molecular composition. Chlorinated organics were observed, which likely originated from chlorine addition to the double bond present on the heterogeneously produced dihydrofurans. A two-dimensional thermogram representation was developed to visualize the composition and relative volatility of organic aerosol components using unit-mass resolution data. Evidence of oligomer formation and thermal decomposition was observed. Aerosol yield and oligomer formation were suppressed under humid conditions (35 % to 67 % RH) relative to dry conditions (under 5 % RH). The temperature at peak desorption signal, Tmax, a proxy for aerosol volatility, was shown to change with aerosol filter loading, which should be constrained when evaluating aerosol volatilities using the FIGAERO–CIMS. Results suggest that long-chain anthropogenic alkanes could contribute significantly to ambient aerosol loading over their atmospheric lifetime.
Herein a novel method was proposed for the fabrication of ceramic membranes by digital light processing (DLP) three-dimensional (3D) printing. The UV-curable alumina suspension was optimized by ...tuning the solid content, grading ratio, and temperature to achieve low viscosity. The Krieger-Dougherty model and the Vogel-Fulcher-Tammann equation were employed to describe and predict the changing trends of viscosity. The effects of the sintering process on the microstructures, mechanical strength, and permeability of the ceramic membranes were also studied. Under the optimized conditions, ceramic membranes were obtained with uniform pore size distribution, high porosity of 42.6%, an average pore size of 0.9 μm, and a pure water flux of 2.66 m3 m-2 h-1 bar-1. Therefore, DLP 3D printing demonstrates good prospects for application in the fabrication of ceramic membranes.
Display omitted
•Ceramic membranes were fabricated by a novel DLP 3D printing method.•The optimized UV-curable alumina suspension with low viscosity was good for printing.•K-D and V–F-T models were successfully employed to predict the change of viscosity.•Ceramic membranes exhibited a uniform pore size distribution.
Recent studies have found concentrations of reactive chlorine species to be higher than expected, suggesting that atmospheric chlorine chemistry is more extensive than previously thought. Chlorine ...radicals can interact with hydroperoxy (HOx) radicals and nitrogen oxides (NOx) to alter the oxidative capacity of the atmosphere. They are known to rapidly oxidize a wide range of volatile organic compounds (VOCs) found in the atmosphere, yet little is known about secondary organic aerosol (SOA) formation from chlorine-initiated photooxidation and its atmospheric implications. Environmental chamber experiments were carried out under low-NOx conditions with isoprene and chlorine as primary VOC and oxidant sources. Upon complete isoprene consumption, observed SOA yields ranged from 7 to 36 %, decreasing with extended photooxidation and SOA aging. Formation of particulate organochloride was observed. A high-resolution time-of-flight chemical ionization mass spectrometer was used to determine the molecular composition of gas-phase species using iodide–water and hydronium–water cluster ionization. Multi-generational chemistry was observed, including ions consistent with hydroperoxides, chloroalkyl hydroperoxides, isoprene-derived epoxydiol (IEPOX), and hypochlorous acid (HOCl), evident of secondary OH production and resulting chemistry from Cl-initiated reactions. This is the first reported study of SOA formation from chlorine-initiated oxidation of isoprene. Results suggest that tropospheric chlorine chemistry could contribute significantly to organic aerosol loading.
Intelligent edge computing carries out edge devices of the Internet of things (IoT) for data collection, calculation and intelligent analysis, so as to proceed data analysis nearby and make feedback ...timely. Because of the mobility of mobile equipments (MEs), if MEs move among the reach of the small cell networks (SCNs), the offloaded tasks cannot be returned to MEs successfully. As a result, migration incurs additional costs. In this paper, joint task offloading and migration schemes in mobility-aware Mobile Edge Computing (MEC) network based on Reinforcement Learning (RL) are proposed to obtain the maximum system revenue. Firstly, the joint optimization problems of maximizing the total revenue of MEs are put forward, in view of the mobility-aware MEs. Secondly, considering time-varying computation tasks and resource conditions, the mixed integer non-linear programming (MINLP) problem is described as a Markov Decision Process (MDP). Then we propose a novel reinforcement learning-based optimization framework to work out the problem, instead traditional methods. Finally, it is shown that the proposed schemes can obviously raise the total revenue of MEs by giving simulation results.
Fog computing is an extension of cloud computing, which emphasizes distributed computing and provides computing service closer to user equipments (UEs). However, due to the limited service coverage ...of fog computing nodes (FCNs), the moving users may be out of the coverage, which would cause the radio handover and execution results migration when the tasks are off-loaded to FCNs. Furthermore, extra cost, including energy consumption and latency, is generated and affects the revenue of UEs. Previous works rarely consider the mobility of UEs in fog computing networks. In this paper, a generic three-layer fog computing networks architecture is considered, and the mobility of UEs is characterized by the sojourn time in each coverage of FCNs, which follows the exponential distribution. To maximize the revenue of UEs, the off-loading decisions and computation resource allocation are jointly optimized to reduce the probability of migration. The problem is modeled as a mixed integer nonlinear programming (MINLP) problem, which is NP-hard. The problem is divided into two parts: tasks off-loading and resource allocation. A Gini coefficient-based FCNs selection algorithm (GCFSA) is proposed to get a sub-optimal off-loading strategy, and a distributed resource optimization algorithm based on genetic algorithm (ROAGA) is implemented to solve the computation resource allocation problem. The proposed algorithms can handle the scenario of UEs' mobility in fog computing networks by significantly reducing the probability of migration. Simulations demonstrate that the proposed algorithms can achieve quasi-optimal revenue performance compared with other baseline algorithms.
Objective. The reported incidence of type 2 diabetes mellitus (T2DM) after gestational diabetes (GDM) varies widely. The purpose of this meta-analysis was to define the incidence rate of T2DM among ...women with a history of GDM and to examine what might modulate the rate. Research Design and Methods. We searched PubMed and Embase for terms related to T2DM after GDM up to January 2019. Large cohort studies with sample size ≥300 and follow-up duration of at least one year were included. Data from selected studies were extracted, and meta-analysis was performed using the random-effects model. Subgroups analyses were based on the sample size of gestational diabetes, geographic region, maternal age, body-mass index, diagnostic criteria, and duration of follow-up. Results. Twenty-eight studies involving 170,139 women with GDM and 34,627 incident cases of T2DM were identified. The pooled incidence of T2DM after GDM was 26.20 (95% CI, 23.31 to 29.10) per 1000 person-years. Women from Asia and those with older age and higher body mass index seem to experience higher risk of developing T2DM. The incidence rate of T2DM was lowest when applying IADPSG (7.16 per 1000 person-years) to diagnose GDM. The risk of developing T2DM after GDM increased linearly with the duration of follow-up. The increments per year of follow-up were estimated at 9.6‰. The estimated risks for T2DM were 19.72% at 10 years, 29.36% at 20 years, 39.00% at 30 years, 48.64% at 40 years, and 58.27% at 50 years, respectively. Conclusions. The findings of very high incidence of T2DM after GDM add an important insight into the trajectory of the development of T2DM in the long-term postpartum periods, which could provide evidence for consultant and might motivate more women with GDM to screen for T2DM. This trial is registered with PROSPERO identifier CRD42019128980.
Fine particulate matter (PM2.5) is a key indicator of urban air quality. Secondary organic aerosol (SOA) contributes substantially to the PM2.5 concentration. Discrepancies between modeling and field ...measurements of SOA indicate missing sources and formation mechanisms. Recent studies report elevated concentrations of reactive chlorine species in inland and urban regions, which increase the oxidative capacity of the atmosphere and serve as sources for SOA and particulate chlorides. Chlorine-initiated oxidation of isoprene, the most abundant nonmethane hydrocarbon, is known to produce SOA under pristine conditions, but the effects of anthropogenic influences in the form of nitrogen oxides (NOx) remain unexplored. Here, we investigate chlorine–isoprene reactions under low- and high-NOx conditions inside an environmental chamber. Organic chlorides including C5H11ClO3, C5H9ClO3, and C5H9ClO4 are observed as major gas- and particle-phase products. Modeling and experimental results show that the secondary OH–isoprene chemistry is significantly enhanced under high-NOx conditions, accounting for up to 40% of all isoprene oxidized and leading to the suppression of organic chloride formation. Chlorine-initiated oxidation of isoprene could serve as a source for multifunctional (chlorinated) organic oxidation products and SOA in both pristine and anthropogenically influenced environments.
The nature of gold active sites on Au–Ti catalysts dictates the reactivity and selectivity during propylene epoxidation reactions. The type of the sites and the location of Au clusters on the ...external surfaces of TS-1 or inside the TS-1 nanopores have remained the topic of interest. We synthesized and characterized dispersed Au clusters on titanium silicate-1 (Au/TS-1), uncalcined TS-1 (Au/un TS-1), and TS-1 coated with silicalite-1 (Au/S-1/TS-1) to probe the nature of gold active sites for gas-phase epoxidation of propylene. The results of Au/TS-1 and Au/S-1/TS-1 show the importance of Au nanoclusters (<1.0 nm) inside TS-1 nanopores. Propylene oxide (PO) rate of Au/un TS-1 suggests Au nanoclusters (<1.0 nm) on the external surfaces also play an important role. On the basis of this conclusion, better performance for direct propylene epoxidation can be developed over Au–Ti catalysts with Au nanoclusters (<1.0 nm) either inside TS-1 nanopores or on the external surfaces.
PDF
