Ultrafine particle | EPFL Graph Search

Ultrafine particles (UFPs) are particulate matter of nanoscale size (less than 0.1 μm or 100 nm in diameter). Regulations do not exist for this size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 particle classes and are believed to have several more aggressive health implications than those classes of larger particulates. In the EU UFP's in ambient air are empirically defined by a technical specification. The important detail is the definition of size, stated: "The lower and upper sizes considered within this document are 7 nm and a few micrometres, respectively". Although the most common referral to UFP is "less than 0.1μm", this is incorrect for ambient air in the EU. There are two main divisions that categorize types of UFPs. UFPs can either be carbon-based or metallic, a

Characterization of surface functional groups present on laboratory-generated and ambient aerosol particles by means of heterogeneous titration reactions

Michel Guillemin, Michel Rossi

A Knudsen flow reactor has been used to quantify surface functional groups on aerosols collected in the field. This technique is based on a heterogeneous titration reaction between a probe gas and a specific functional group on the particle surface. In the first part of this work, the reactivity of different probe gases on laboratory-gene rated aerosols (limonene SOA, Pb(NO3)(2), Cd(NO3)(2)) and diesel reference soot (SRM 2975) has been studied. Five probe gases have been selected for the quantitative determination of important functional groups: N(CH3)(3) (for the titration of acidic sites), NH2OH (for carbonyl functions), CF3COOH and HCl (for basic sites of different strength), and O-3 (for oxidizable groups). The second part describes a field campaign that has been undertaken in several bus depots in Switzerland, where ambient fine and ultrafine particles were collected on suitable filters and quantitatively investigated using the Knudsen flow reactor. Results point to important differences in the surface reactivity of ambient particles, depending on the sampling site and season. The particle surface appears to be multi-functional, with the simultaneous presence of antagonistic functional groups which do not undergo internal chemical reactions, such as acid-base neutralization. Results also indicate that the surface of ambient particles was characterized by a high density of carbonyl functions (reactivity towards NH2OH probe in the range 0.26-6 formal molecular monolayers) and a low density of acidic sites (reactivity towards N(CH3)(3) probe in the range 0.01-0.20 formal molecular monolayer). Kinetic parameters point to fast redox reactions (uptake coefficient y(0) > 10(-3) for O-3 probe) and slow acid-base reactions (gamma(0) < 10(-4) for N(CH3)(3) probe) on the particle surface. (C) 2009 Elsevier Ltd. All rights reserved.

2009

Numerical Simulations of an Innovative Water Stirring Device for Fine Sediment Release: The Case Study of the Future Trift Reservoir

Azin Amini, Anass Chraibi, Pedro Filipe De Almeida Manso

Reservoir sedimentation and consequently lack of storage volume and perturbation of the operation of intakes and bottom outlet is a key challenge affecting both hydropower production as well as dam safety and flood management. In the framework of a peer-reviewed research project (Jenzer-Althaus, 2011) an innovative countermeasure, called SEDMIX, was proposed allowing to keep in suspension or re-suspend the fine particles near the power water intakes, thanks to an optimized arrangement of four water jets producing an upward whirling flow like produced by a mixer. With such a system, the suspended particles can be conveyed downstream at acceptable rates through the power waterways during the normal operation of the hydropower plant. Although experimental studies have shown the very promising efficiency of such a device in simple cases and by numerical simulations in a laboratory reservoir, SEDMIX performance has not been investigated yet in a real-life reservoir under prototype conditions. The aim of this study is therefore, to analyze the performance of a real-sized SEDMIX operating in the future Trift reservoir via numerical analyses. This study allows to validate or to improve SEDMIX optimal configuration experimentally determined. The numerical simulations are performed for different positions and heights for the SEDMIX device. The performance of SEDMIX in each position has been evaluated and tested for different jet discharges. The analysis of the numerical simulation results shows that the presence of SEDMIX does create a vortex flow pattern and sediment movement upward. The sediment volume fraction in the higher layers of the reservoir increases and consequently the evacuated volume of fin sediments increases for simulation using the SEDMIX device comparing those without the device.

Springer2020

Molecular characterization of ultrafine particles using extractive electrospray time-of-flight mass spectrometry

Andrea Baccarini, Lubna Dada

Aerosol particles negatively affect human health while also having climatic relevance due to, for example, their ability to act as cloud condensation nuclei. Ultrafine particles (diameter Dp < 100 nm) typically comprise the largest fraction of the total number concentration, however, their chemical characterization is difficult because of their low mass. Using an extractive electrospray time-of-flight mass spectrometer (EESI-TOF), we characterize the molecular composition of freshly nucleated particles from naphthalene and β-caryophyllene oxidation products at the CLOUD chamber at CERN. We perform a detailed intercomparison of the organic aerosol chemical composition measured by the EESI-TOF and an iodide adduct chemical ionization mass spectrometer equipped with a filter inlet for gases and aerosols (FIGAERO-I-CIMS). We also use an aerosol growth model based on the condensation of organic vapors to show that the chemical composition measured by the EESI-TOF is consistent with the expected condensed oxidation products. This agreement could be further improved by constraining the EESI-TOF compound-specific sensitivity or considering condensed-phase processes. Our results show that the EESI-TOF can obtain the chemical composition of particles as small as 20 nm in diameter with mass loadings as low as hundreds of ng m−3 in real time. This was until now difficult to achieve, as other online instruments are often limited by size cutoffs, ionization/thermal fragmentation and/or semi-continuous sampling. Using real-time simultaneous gas- and particle-phase data, we discuss the condensation of naphthalene oxidation products on a molecular level.

2021