Liquid metals as electrodes in polymer light emitting diodes

We demonstrate that liquid metals can be used as cathodes in light emitting diodes (pLEDs). The main difference between the use of liquid cathodes and evaporated cathodes is the sharpness of the metal–polymer interface. Liquid metal cathodes result in significantly sharper metal–organic interfaces than vapor deposited cathodes, due to the high surface energy of the metals. The sharper interface in pLEDs with liquid metal cathodes is observed by neutral impact collision ion scattering spectroscopy and low energy ion scattering spectroscopy measurements. The influence of interface sharpness on device performance was studied by comparing current–voltage-light characteristics of devices with OC1C10 paraphenylenevinylene (PPV) as electroluminescent polymer and indium tin oxide (ITO) as hole injection electrode, and different cathodes. Comparison of devices using a liquid Ga cathode and an evaporated Al cathode showed that light emission for the liquid Ga cathode is two orders of magnitude larger than for the evaporated Al cathode, and that the external light efficiency is increased by an order of magnitude. Since the work function of Ga and Al is nearly the same, the poor performance for evaporated Al LEDs is attributed to the formation of an interfacial layer where Al has diffused into, and reacted with, the PPV. This interfacial layer has poor electrical conduction compared to pure PPV, and contains quenching sites which reduce light emission. Low work function liquid metal cathodes were studied by using liquid Ca and Ba amalgams. The improved performance of liquid amalgam pLEDs is attributed to the different structure of the metal–polymer interface. The enormous increase in light and current through the amalgam devices compared to those using pure Hg demonstrate that less than 1 ML of a metal with a low work function at the polymer-cathode interface can have a dramatic effect on the performance of the devices. Devices with a liquid Ca amalgam cathode showed an increase of the current (by 50%) and brightness (80%) compared to devices with an evaporated Ca cathode, which is ascribed to reduced diffusion of Ca into the emissive PPV laye

Modelling the chemically aged and mixed aerosols over the eastern central Atlantic Ocean – potential impacts

Detailed information on the chemical and physical properties of aerosols is important for assessing their role in air quality and climate. This work explores the origin and fate of continental aerosols transported over the Central Atlantic Ocean, in terms of chemical composition, number and size distribution, using chemistry-transport models, satellite data and in situ measurements. We focus on August 2005, a period with intense hurricane and tropical storm activity over the Atlantic Ocean. A mixture of anthropogenic (sulphates, nitrates), natural (desert dust, sea salt) and chemically aged (sulphate and nitrate on dust) aerosols is found entering the hurricane genesis region, most likely interacting with clouds in the area. Results from our modelling study suggest rather small amounts of accumulation mode desert dust, sea salt and chemically aged dust aerosols in this Atlantic Ocean region. Aerosols of smaller size (Aitken mode) are more abundant in the area and in some occasions sulphates of anthropogenic origin and desert dust are of the same magnitude in terms of number concentrations. Typical aerosol number concentrations are derived for the vertical layers near shallow cloud formation regimes, indicating that the aerosol number concentration can reach several thousand particles per cubic centimetre. The vertical distribution of the aerosols shows that the desert dust particles are often transported near the top of the marine cloud layer as they enter into the region where deep convection is initiated. The anthropogenic sulphate aerosol can be transported within a thick layer and enter the cloud deck through multiple ways (from the top, the base of the cloud, and by entrainment). The sodium (sea salt related) aerosol is mostly found below the cloud base. The results of this work may provide insights relevant for studies that consider aerosol influences on cloud processes and storm development in the Central Atlantic region

Methane and ethane emission scenarios for potential shale gas production in Europe

A main concern surrounding (shale) gas production and exploitation is the leakage of methane, a potent greenhouse gas. High leakage rates have been observed outside of Europe but the representativeness of these observations for Europe is unknown. To facilitate the monitoring of methane leakage from a future shale gas industry in Europe we developed potential production scenarios for ten major shale gas plays and identified a suitable tracer in (shale) gas to distinguish oil and gas related emissions from other methane sources. To distinguish gas leakage from other methane sources we propose ethane, a known tracer for leakage from oil and gas production but absent in emissions from other important methane sources in Europe. Ethane contents for the ten plays are estimated from a European gas composition database and shale gas composition and reservoir data from the US, resulting in three different classes of ethane to methane ratios in the raw gas (0.015, 0.04 and 0.1). The ethane content classes have a relation with the average thermal maturity, a basic shale gas reservoir characteristic, which is known for all ten European shale gas plays. By assuming different production scenarios in addition to a range of possible gas leakage rates, we estimate potential ethane tracer release by shale gas play. Ethane emissions are estimated by play following a low, medium or high gas production scenario in combination with leakage rates ranging from 0.2&thinsp;%–10&thinsp;% based on observed leakage rates in the US.</p

Aerosol Particle Number Emissions and Size Distributions: Implementation in the GAINS Model and Initial Results

Particulate matter affects our health and climate. In addition to well based knowledge on the adverse health effects related to particle mass concentrations, there is increasing evidence showing that the number concentrations of ultra-fine aerosol particles, with diameters below 0.1 um, have negative health impacts, which are significantly different from those caused by larger particles with sizes over 1 um. Particles with diameters between 0.1 and 1 um can also be activated as cloud droplets; thereby, higher number concentrations can increase the cloud albedo and thus the proportion of solar radiation reflected back to space, causing a cooling aerosol climate effect. In addition to this indirect effect, aerosol particles affect Earth radiation budget directly by either scattering solar radiation (e.g. sulphate aerosol, cooling effect) or absorbing it (black carbon aerosol, warming effect). Currently, European air quality legislation on particulate matter is mainly focussing on particle mass, although emission standards for particle numbers have been introduced for mobile sources. Mass concentration is dominated by particles larger than 0.1 um, and it is not well associated with number concentration, due to the often different formation mechanisms of ultra-fine and larger particles. For combustion sources, some emission control technologies affect mainly large particle emissions, and may even increase emissions of ultra-fine particles. Hence, in order to comprehensively estimate health and climate effects of anthropogenic aerosol particles, it is necessary to quantify their emissions with both mass and number based metrics, including information on their size distribution. Currently, European air quality legislation on particulate matter is mainly focussing on particle mass, although emission standards for particle numbers have been introduced for mobile sources. Mass concentration is dominated by particles larger than 0.1 um, and it is not well associated with number concentration, due to the often different formation mechanisms of ultra-fine and larger particles. For combustion sources, some emission control technologies affect mainly large particle emissions, and may even increase emissions of ultra-fine particles. Hence, in order to comprehensively estimate health and climate effects of anthropogenic aerosol particles, it is necessary to quantify their emissions with both mass and number based metrics, including information on their size distribution. This report describes the implementation of size segregated particle number emission calculations in the GAINS model. Results show that in 2010 in Europe more than 60% of particle number emissions emerge from road transport, even though their share in total PM1 mass emissions (i.e., the mass of emitted particles with diameters below 1 um) is only 12%. Particle number emissions from road transport are expected to decrease rapidly in the future due to further tightening of exhaust emission legislation (EURO-standards). Due to the envisaged more pronounced particle number emission reduction in the road transport sector compared to the currently second and third largest source sectors, shipping and combustion of fuel wood and coal in the residential sector, emissions from the latter two sectors are anticipated to exceed road transport emissions by 2025. Estimated shares in total European emissions in 2025 range, depending on the applied future scenario, from 35 to 41% for shipping, from 26 to 29% for residential combustion and from 17 to 21% for road transport. The presented initial results are, however, subject to significant uncertainties, primarily due to limited measurement data for several emission sources

Global anthropogenic particle number emissions and their size distributions

Aerosol particle number concentrations and size distributions affect our climate by determining the formation of cloud droplets and thus altering the cloud reflective properties. The aerosol-cloud interactions are one of the main uncertainties in estimating the future climate change. One of the weaknesses in current climate modelling is the description of number emissions and size distributions of particles. Here, we present the first global results of implementing particle number emission factors to GAINS emission scenario model and discuss the related uncertainties. The uncertainties for different source sectors vary significantly, causing a steep difference in total uncertainties in different parts of the world. The reason for these uncertainties is the scarcity of data on particle number size distributions for certain sources. The implemented particle number emission factors, however, are expected to be a significant improvement over previously applied particle number emissions estimates in climate modelling

Advancing global aerosol simulations with size-segregated anthropogenic particle number emissions

Climate models are important tools that are used for generating climate change projections, in which aerosol-climate interactions are one of the main sources of uncertainties. In order to quantify aerosol-radiation and aerosolcloud interactions, detailed input of anthropogenic aerosol number emissions is necessary. However, the anthropogenic aerosol number emissions are usually converted from the corresponding mass emissions in pre-compiled emission inventories through a very simplistic method depending uniquely on chemical composition, particle size and density, which are defined for a few, very wide main source sectors. In this work, the anthropogenic particle number emissions converted from the AeroCom mass in the ECHAM-HAM climate model were replaced with the recently formulated number emissions from the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model. In the GAINS model the emission number size distributions vary, for example, with respect to the fuel and technology. Special attention was paid to accumulation mode particles (particle diameter d(p) > 100 nm) because of (i) their capability of acting as cloud condensation nuclei (CCN), thus forming cloud droplets and affecting Earth's radiation budget, and (ii) their dominant role in forming the coagulation sink and thus limiting the concentration of sub-100 nm particles. In addition, the estimates of anthropogenic CCN formation, and thus the forcing from aerosol-climate interactions, are expected to be affected. Analysis of global particle number concentrations and size distributions reveals that GAINS implementation increases CCN concentration compared with AeroCom, with regional enhancement factors reaching values as high as 10. A comparison between modeled and observed concentrations shows that the increase in number concentration for accumulation mode particles agrees well with measurements, but it leads to a consistent underestimation of both nucleation mode and Aitken mode (d(p) <100 nm) particle number concentrations. This suggests that revisions are needed in the new particle formation and growth schemes currently applied in global modeling frameworks.Peer reviewe

Interface formation in K doped poly(dialkoxy-p-phenylene vinylene) light-emitting diodes

Manufacturing of Al/K/OC1C10 poly(p-phenylene vinylene)/indium–tin–oxide light emitting diode structures by physical vapor deposition of K onto the emissive polymer layer has been characterized by electroluminescence and ion spectroscopy. Varying the deposited K areal density from 3.9×1012 to 1.2×1014 atoms cm−2 the external efficiency rises from 0.01 to 1.2 Cd A−1. Spectra obtained by ion scattering analysis demonstrate the overall absence of K at the polymer outermost surface layer, and diffusion up to a depth of 200 Å. Depth profiles have been derived, and were modeled using an irreversible first order “trapping” reaction. Trapping may stem from confinement of the electron at a conjugated segment, that was donated through charge transfer typical for alkali/π-conjugated systems. This study demonstrates that evaporation of low work function metals onto organic systems should not be depicted as simple layered stacking structures. The enhanced electroluminescence with submonolayer K deposition is attributed to the shift of the recombination zone away from the Al cathode, which is demonstrated to prevail over the known exciton quenching mechanism due to the formation of gap states

Intercomparison of detection and quantification methods for methane emissions from the natural gas distribution network in Hamburg, Germany

In August and September 2020, three different measurement methods for quantifying methane (CH4) emissions from leaks in urban gas distribution networks were applied and compared in Hamburg, Germany: the “mobile”, “tracer release”, and “suction” methods. The mobile and tracer release methods determine emission rates to the atmosphere from measurements of CH4 mole fractions in the ambient air, and the tracer release method also includes measurement of a gaseous tracer. The suction method determines emission rates by pumping air out of the ground using soil probes that are placed above the suspected leak location. The quantitative intercomparison of the emission rates from the three methods at a small number of locations is challenging because of limitations of the different methods at different types of leak locations. The mobile method was designed to rapidly quantify the average or total emission rate of many gas leaks in a city, but it yields a large emission rate uncertainty for individual leak locations. Emission rates determined for individual leak locations with the tracer release technique are more precise because the simultaneous measurement of the tracer released at a known rate at the emission source eliminates many of the uncertainties encountered with the mobile method. Nevertheless, care must be taken to properly collocate the tracer release and the leak emission points to avoid biases in emission rate estimates. The suction method could not be completed or applied at locations with widespread subsurface CH4 accumulation or due to safety measures. While the number of gas leak locations in this study is small, we observe a correlation between leak emission rate and subsurface accumulation. Wide accumulation places leaks into a safety category that requires immediate repair so that the suction method cannot be applied to these larger leaks in routine operation. This introduces a sampling bias for the suction method in this study towards the low-emission leaks, which do not require immediate repair measures. Given that this study is based on random sampling, such a sampling bias may also exist for the suction method outside of this study. While an investigation of the causal relationship between safety category and leak size is beyond the scope of this study, on average higher emission rates were observed from all three measurement-based quantification methods for leaks with higher safety priority compared to the leaks with lower safety concern. The leak locations where the suction method could not be applied were the biggest emitters, as confirmed by the emission rate quantifications using mobile and tracer methods and an engineering method based on the leak's diameter, pipeline overpressure, and depth at which the pipeline is buried. The corresponding sampling bias for the suction technique led to a low bias in derived emission rates in this study. It is important that future studies using the suction method account for any leaks not quantifiable with this method in order to avoid biases, especially when used to inform emission inventories.</p