Performance comparison of two thermodenuders in Volatility Tandem DMA measurements

AbstractVolatility Tandem Differential Mobility Analysers (VTDMAs) are widely used for determining the volatile and refractory fractions and thus the mixing state of aerosols particles. A three-channel VTDMA consisting of two thermodenuders (TDs) with distinct designs (i.e., the NanoTD, having a straight tube design, and a coiled TD; cTD) and a by-pass line was built and fully characterized. Both TDs were tested using laboratory-generated aerosol particles (single compound and core–shell particles) as well as atmospheric aerosols observed at an urban background station. The NanoTD exhibited high particle penetration efficiency and negligible thermophoretic losses, making it advantageous for ultrafine particle analysis, especially in environments with low particle concentration. The cTD allows longer particle residence time for the same flow rate, resulting in higher particle volatilization in some cases. Higher particle losses in this TD, both thermophoretic and diffusional, pose a limitation when dealing with low particle concentrations.The difference in the performance between the thermodenuders was only noticed at intermediate temperatures, at which particle volume loss becomes more pronounced. These temperatures vary among aerosols, since the volatilization rate depends on the chemical complexity and size of the particles sampled. Differences in the aerosol volume fraction remaining after heating with the two TD designs exhibited a maximum of 20% for single-compound particles and 12% for urban background aerosols. Measurements using core–shell particles yielded differences of up to 21% in particle volatilization, independently of particle size, when comparing the system using either of the two TD designs. Similar results were obtained with the two TD designs at higher operating temperatures (e.g., 230°C), indicating that at this temperature most of the material on the particles was evaporated

Vertical profiles of aerosol mass concentration derived by unmanned airborne in situ and remote sensing instruments during dust events

In situ measurements using unmanned aerial vehicles (UAVs) and remote sensing observations can independently provide dense vertically resolved measurements of atmospheric aerosols, information which is strongly required in climate models. In both cases, inverting the recorded signals to useful information requires assumptions and constraints, and this can make the comparison of the results difficult. Here we compare, for the first time, vertical profiles of the aerosol mass concentration derived from light detection and ranging (lidar) observations and in situ measurements using an optical particle counter on board a UAV during moderate and weak Saharan dust episodes. Agreement between the two measurement methods was within experimental uncertainty for the coarse mode (i.e. particles having radii  > 0.5µm), where the properties of dust particles can be assumed with good accuracy. This result proves that the two techniques can be used interchangeably for determining the vertical profiles of aerosol concentrations, bringing them a step closer towards their systematic exploitation in climate models

The Unmanned Systems Research Laboratory (USRL)

The Unmanned Systems Research Laboratory (USRL) of the Cyprus Institute is a new mobile exploratory platform of the EU Research Infrastructure Aerosol, Clouds and Trace Gases Research InfraStructure (ACTRIS). USRL offers exclusive Unmanned Aerial Vehicle (UAV)-sensor solutions that can be deployed anywhere in Europe and beyond, e.g., during intensive field campaigns through a transnational access scheme in compliance with the drone regulation set by the European Union Aviation Safety Agency (EASA) for the research, innovation, and training. UAV sensor systems play a growing role in the portfolio of Earth observation systems. They can provide cost-effective, spatial in-situ atmospheric observations which are complementary to stationary observation networks. They also have strong potential for calibrating and validating remote-sensing sensors and retrieval algorithms, mapping close-to-the-ground emission point sources and dispersion plumes, and evaluating the performance of atmospheric models. They can provide unique information relevant to the short- and long-range transport of gas and aerosol pollutants, radiative forcing, cloud properties, emission factors and a variety of atmospheric parameters. Since its establishment in 2015, USRL is participating in major international research projects dedicated to (1) the better understanding of aerosol-cloud interactions, (2) the profiling of aerosol optical properties in different atmospheric environments, (3) the vertical distribution of air pollutants in and above the planetary boundary layer, (4) the validation of Aeolus satellite dust products by utilizing novel UAV-balloon-sensor systems, and (5) the chemical characterization of ship and stack emissions. A comprehensive overview of the new UAV-sensor systems developed by USRL and their field deployments is presented here. This paper aims to illustrate the strong scientific potential of UAV-borne measurements in the atmospheric sciences and the need for their integration in Earth observation networks

Internally mixed nanoparticles from oscillatory spark ablation between electrodes of different materials

<p>The increasing need for engineered alloy nanoparticles (NPs) in diverse fields has spurred efforts to explore efficient/green synthesis methods. In this respect, spark ablation provides a scalable and viable way for producing widely different types of mixed NPs. Most importantly, implementation of the spark has the great advantage to combine a wider range of materials, thereby allowing the synthesis of mixed NPs with virtually unlimited combinations. Here we show that polarity reversal of spark discharges between two electrodes consisting of different materials enables synthesis of alloy NPs, while having a good potential to control the broadness of their composition distribution. A model developed in this work provides a tool for tuning the ablation ratio between the electrodes by adjusting the electric characteristics of the spark circuit. The ablation ratio is equal to the mean composition of the resulting NPs. The model predictions are in accordance with measurements obtained here and in earlier works. The unique way of producing alloy NPs by spark ablation shown in this work becomes especially useful when the starting electrode materials are immiscible at macroscopic scale.</p> <p>Copyright © 2018 American Association for Aerosol Research</p

The regime of Aerosol Optical Depth and Ångström exponent over Central and South Asia

Central and South Asia are regions of particular interest for studying atmospheric aerosols, being among the largest sources of desert dust aerosols globally. In this study we use the newest collection (C061) of MODIS - Aqua aerosol optical depth (AOD) at 550 nm and Ångström exponent (a) at 412/470 nm over the 15-year period between 2002 and 2017, providing the longest analyzed dataset for this region. According to our results, during spring and summer, high aerosol load (AOD up to 1.2) consisting of coarse desert dust particles, as indicated by a values as low as 0.15, is observed over the Taklamakan, Thar and Registan deserts and the region between the Aral and Caspian seas. The dust load is much lower during winter and autumn (lower AOD and higher a values compared to the other seasons). The interannual variation of AOD and a suggests that the dust load exhibits large decreasing trends (AOD slopes down to -0.22, a slopes up to 0.47 decade-1) over the Thar desert and large increasing trends between the Aral and Caspian seas (AOD and a slopes up to 0.23 decade-1 and down to -0.61 decade-1, respectively.) The AOD data are evaluated against AERONET surface-based measurements. Generally, MODIS and AERONET data are in good agreement with a correlation coefficient (R) equal to 0.835

Engineered nanomaterials:Knowledge gaps in fate, exposure, toxicity, and future directions

The aim of this study is to identify current knowledge gaps in fate, exposure, and toxicity of engineered nanomaterials (ENMs), highlight research gaps, and suggest future research directions. Humans and other living organisms are exposed to ENMs during production or use of products containing them. To assess the hazards of ENMs, it is important to assess their physiochemical properties and try to relate them to any observed hazard. However, the full determination of these relationships is currently limited by the lack of empirical data. Moreover, most toxicity studies do not use realistic environmental exposure conditions for determining dose-response parameters, affecting the accurate estimation of health risks associated with the exposure to ENMs. Regulatory aspects of nanotechnology are still developing and are currently the subject of much debate. Synthesis of available studies suggests a number of open questions. These include (i) developing a combination of different analytical methods for determining ENM concentration, size, shape, surface properties, and morphology in different environmental media, (ii) conducting toxicity studies using environmentally relevant exposure conditions and obtaining data relevant to developing quantitative nanostructure-toxicity relationships (QNTR), and (iii) developing guidelines for regulating exposure of ENMs in the environment