30 research outputs found
Confined colloidal crystals in and out of equilibrium
Recent studies on confined crystals of charged colloidal particles are
reviewed, both in equilibrium and out of equilibrium. We focus in particular on
direct comparisons of experiments (light scattering and microscopy) with
lattice sum calculations and computer simulations. In equilibrium we address
buckling and crystalline multilayering of charged systems in hard and soft slit
confinement. We discuss also recent crystalline structures obtained for charged
mixtures. Moreover, we put forward possibilities to apply external
perturbations, in order to drive the system out of equilibrium. These include
electrolyte gradients as well as the application of shear and electric fields.Comment: Review article, 18 pages, 5 figure
Application of mobile aerosol and trace gas measurements for the investigation of megacity air pollution emissions: the Paris metropolitan area
For the investigation of megacity emission development and the impact outside the
source region, mobile aerosol and trace gas measurements were carried out in
the Paris metropolitan area between 1 July and 31 July 2009 (summer
conditions) and 15 January and 15 February 2010 (winter conditions) in the
framework of the European Union FP7 MEGAPOLI project. Two mobile
laboratories, MoLa and MOSQUITA, were deployed, and here an overview of these
measurements and an investigation of the applicability of such measurements
for the analysis of megacity emissions are presented. Both laboratories
measured physical and chemical properties of fine and ultrafine aerosol
particles as well as gas phase constituents of relevance for urban pollution
scenarios. The applied measurement strategies include cross-section
measurements for the investigation of plume structure and quasi-Lagrangian
measurements axially along the flow of the city's pollution plume to study
plume aging processes. Results of intercomparison measurements between the
two mobile laboratories represent the adopted data quality assurance
procedures. Most of the compared measurement devices show sufficient
agreement for combined data analysis. For the removal of data contaminated by
local pollution emissions a video tape analysis method was applied. Analysis
tools like positive matrix factorization and peak integration by key analysis
applied to high-resolution time-of-flight aerosol mass spectrometer data are
used for in-depth data analysis of the organic particulate matter. Several
examples, including a combination of MoLa and MOSQUITA measurements
on a cross section through the Paris emission plume, are provided to demonstrate
how such mobile measurements can be used to investigate the emissions of a
megacity. A critical discussion of advantages and limitations of mobile
measurements for the investigation of megacity emissions completes this work
Ion size effects on the electrokinetics of salt-free concentrated suspensions in ac fields
We analyze the influence of finite ion size effects in the response of a
salt-free concentrated suspension of spherical particles to an oscillating
electric field. Salt-free suspensions are just composed of charged colloidal
particles and the added counterions released by the particles to the solution,
that counterbalance their surface charge. In the frequency domain, we study the
dynamic electrophoretic mobility of the particles and the dielectric response
of the suspension. We find that the Maxwell-Wagner-O'Konski process associated
with the counterions condensation layer, is enhanced for moderate to high
particle charges, yielding an increment of the mobility for such frequencies.
We also find that the increment of the mobility grows with ion size and
particle charge. All these facts show the importance of including ion size
effects in any extension attempting to improve standard electrokinetic models.Comment: J. Colloid Interface Sci., in press, 13 pages, 9 figure
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In situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity
A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70 % of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radiocarbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20 % in winter and 40 % in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin, i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant, flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies
In situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity
International audiencePublished by Copernicus Publications on behalf of the European Geosciences Union. 9578 M. Beekmann et al.: Evidence for a dominant regional contribution to fine particulate matter levels Abstract. A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70 % of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radio-carbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20 % in winter and 40 % in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin , i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant , flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies
Heterogeneous nucleation and microstructure formation: Steps towards a system and scale bridging understanding
Single-use surgical clothing system for reduction of airborne bacteria in the operating room
It is desirable to maintain a low bacterial count in the operating room air to prevent surgical site infection. This can be achieved by ventilation or by all staff in the operating room wearing clothes made from low-permeable material (i.e. clean air suits). We investigated whether there was a difference in protective efficacy between a single-use clothing system made of polypropylene and a reusable clothing system made of a mixed material (cotton/polyester) by testing both in a dispersal chamber and during surgical procedures. Counts of colony-forming units (cfu)/m(3) air were significantly lower when using the single-use clothing system in both settings
Structure and transport properties of charged sphere suspensions in (local) electric fields
Motivated by both still open fundamental theoretical questions as well as novel applications, the electro-kinetics of highly charged model colloids have attracted considerable interest in the last few years. The present paper reviews corresponding new developments and trends emerging mainly from novel instrumentations for both strongly interacting and extremely dilute systems. We also highlight recent uses of local electric fields and electro-kinetic currents to realize complex micro-swimmers or prescribe crystal micro-structures