Showing papers by "George Biskos published in 2017"

Hot Carrier Generation and Extraction of Plasmonic Alloy Nanoparticles

Abstract: The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of parti...

Investigation of Turbulence Parametrization Schemes with Reference to the Atmospheric Boundary Layer Over the Aegean Sea During Etesian Winds

Abstract: The spatial structure of the marine atmospheric boundary layer (MABL) over the Aegean Sea is investigated using the Weather Research and Forecasting (WRF) mesoscale model. Two ‘first-order’ non-local and five ‘1.5-order’ local planetary boundary-layer (PBL) parametrization schemes are used. The predictions from the WRF model are evaluated against airborne observations obtained by the UK Facility for Airborne Atmospheric Measurements BAe-14 research aircraft during the Aegean-GAME field campaign. Statistical analysis shows good agreement between measurements and simulations especially at low altitude. Despite the differences between the predicted and measured wind speeds, they reach an agreement index of 0.76. The simulated wind-speed fields close to the surface differ substantially among the schemes (maximum values range from 13 to $$18\hbox { m s}^{-1}$$ at 150-m height), but the differences become marginal at higher levels. In contrast, all schemes show similar spatial variation patterns in potential temperature fields. A warmer (1–2 K) and drier (2–3 $$\hbox { g kg}^{-1})$$ layer than is observed, is predicted by almost all schemes under stable conditions (eastern Aegean Sea), whereas a cooler (up to 2 K) and moister (1–2 $$\hbox { g kg}^{-1})$$ layer is simulated under near-neutral to nearly unstable conditions (western Aegean Sea). Almost all schemes reproduce the vertical structure of the PBL and the shallow MABL (up to 300 m) well, including the low-level jet in the eastern Aegean Sea, with non-local schemes being closer to observations. The simulated PBL depths diverge (up to 500 m) due to the different criteria applied by the schemes for their calculation. Under stable conditions, the observed MABL depth corresponds to the height above the sea surface where the simulated eddy viscosity reaches a minimum; under neutral to slightly unstable conditions this is close to the top of the simulated entrainment layer. The observed sensible heat fluxes vary from −40 to $$25\hbox { W m}^{-2}$$ , while the simulated fluxes range from −40 to $$40\hbox { W m}^{-2}$$ ; however, all of the schemes’ predictions are close to the observations under unstable conditions. Finally, all schemes overestimate the friction velocity, although the simulated range (from 0.2 to $$0.5\hbox { m s}^{-1})$$ is narrower than that observed (from 0.1 to $$0.7\hbox { m s}^{-1})$$ .

A tunable high-pass filter for simple and inexpensive size-segregation of sub-10-nm nanoparticles

Abstract: Recent advanced in the fields of nanotechnology and atmospheric sciences underline the increasing need for sizing sub-10-nm aerosol particles in a simple yet efficient way. In this article, we develop, experimentally test and model the performance of a High-Pass Electrical Mobility Filter (HP-EMF) that can be used for sizing nanoparticles suspended in gaseous media. Experimental measurements of the penetration of nanoparticles having diameters down to ca 1nm through the HP-EMF are compared with predictions by an analytic, a semi-empirical and a numerical model. The results show that the HP-EMF effectively filters nanoparticles below a threshold diameter with an extremely high level of sizing performance, while it is easier to use compared to existing nanoparticle sizing techniques through design simplifications. What is more, the HP-EMF is an inexpensive and compact tool, making it an enabling technology for a variety of applications ranging from nanomaterial synthesis to distributed monitoring of atmospheric nanoparticles.

Impact of Chemical Composition on NPF, CCN and Droplet Formation at South Aegean Sea During Summertime Etesians

Abstract: Atmospheric new particle formation (NPF) is a frequent phenomenon that occurs over the Eastern Mediterranean (EM) atmosphere during Etesians. Particle size distributions (<850 nm), atmospheric oxidants (O3, NO2, SO2) and the chemical composition of the particulate matter were studied from 15 to 28 of July 2013, at a temporary remote coastal station on Santorini and at the remote background site of Finokalia, Crete. Based on in situ simultaneous ground level measurements at both sites, two noticeable episodes of high nucleation-mode particle number concentrations were observed on 23 and 24 July. These atmospheric particles in the nucleation mode (≤25 nm) associated with strong northern winds, shift slowly to larger sizes, consistent with the behavior associated with regional NPF events. From the evolution of number particle concentrations with diameter ~100 nm we derive the variance in CCN after NPF at both stations. Based on cloud droplet calculations the contribution of NPF to supersaturation and droplet number is estimated.

Air Pollution Modeling in a North Aegean City: Effects of the Transportation System on Local Air Quality

Abstract: We use the AERMOD atmospheric dispersion modeling system in order to investigate how the spatial distribution of PM10 is affected by the transportation system (i.e., road traffic and shipping activity at the port) in the city of Mytilene, Greece. AERMOD is a steady-state Gaussian plume model recommended by the US Environmental Protection Agency (EPA), and one of the most widely used models for regulatory purposes. Simulations of the PM10 concentrations are performed for the period 1 to 10 July 2014, with the emissions by road transport being estimated using COPERT 4 v.10 and distributed spatially and temporarily over the road network of Mytilene. Estimations of the shipping emissions were performed using the Tier 3 EMEP methodology. The required meteorological data for the application of AERMOD were taken from the Hellenic National Meteorological Service (HNMS) weather station of Mytilene (surface data) and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (upper air data). Preliminary results indicate that the road traffic emissions contribute to the ambient PM10 concentrations up to 10 μg/m3 (daily averaged values) in the city center. The results of the simulations are compared with in situ PM10 measurements performed during the study period in the city.

UAV measurements of aerosol properties at the Cyprus institute

Abstract: (1) The Cyprus Institute, EEWRC, Cyprus (k.neitola@cyi.ac.cy), (2) NOAA Earth System Research Laboratory, Boulder, CO, USA, (3) Institute for Atmospheric and Environmental Sciences, Goethe University, Frankfurt, Germany, (4) Aerosol do.o.o., Ljubljana, Slovenia, (5) Josef Stefan Institute, Ljubliana, Slovenia, (6) 6 Institute of Environmental Physics and Remote Sensing (IUP), University of Bremen, Germany, (7) Center of Marine Environmental Sciences (MARUM), University of Bremen, Germany