Chemical Properties Of Particles Research Articles

Fluorescent lifetime imaging of atmospheric aerosols: a direct probe of aerosol viscosity

The viscosity of atmospheric aerosol particles affects a number of key physical and chemical particle properties, such as composition and reactivity. However, determination of the microscopic viscosity of aerosol particles is a non-trivial task. We report a new method of imaging viscosity in a variety of model aerosol systems, based on a fluorescence lifetime determination of viscosity-sensitive fluorophores termed molecular rotors. We report the viscosity changes associated with the relative humidity dependent hygroscopicity of NaCI and sucrose aerosols, as well as reaction dependent changes in viscosity during ozonolysis of oleic acid aerosols. The Fluorescence Lifetime Imaging Microscopy (FLIM) of molecular rotors shows great promise in understanding important fundamental aerosol properties, which can be both time-dependent and spatially variable through the aerosol particle.

Mass spectrometric approaches for chemical characterisation of atmospheric aerosols: critical review of the most recent advances

Environmental contextAtmospheric aerosols have profound effects on the environment through several physicochemical processes, such as absorption and scattering of sunlight, heterogeneous gas–particle reactions and adverse effects on the respiratory and cardiovascular systems. Understanding aerosol atmospheric chemistry and its environmental impact requires comprehensive characterisation of the physical and chemical properties of particles. Results from mass spectrometry provide important new insights into the origin of atmospheric aerosols, the evolution of their physicochemical properties, their reactivity and their effect on the environment. AbstractThis manuscript presents an overview of the most recent instrument developments for the field and laboratory applications of mass spectrometry (MS) to investigate the chemistry and physics of atmospheric aerosols. A range of MS instruments, employing different sample introduction methods, ionisation and mass detection techniques are used both for ‘online’ and ‘offline’ characterisation of aerosols. Online MS techniques enable detection of individual particles with simultaneous measurement of particle size distributions and aerodynamic characteristics and are ideally suited for field studies that require high temporal resolution. Offline MS techniques provide a means for detailed molecular-level analysis of aerosol samples, which is essential to gain fundamental knowledge regarding aerosol chemistry, mechanisms of particle formation and atmospheric aging. Combined, complementary MS techniques provide comprehensive information on the chemical composition, size, morphology and phase of aerosols – data of key importance for evaluating hygroscopic and optical properties of particles, their health effects, understanding their origins and atmospheric evolution. Over the last few years, developments and applications of MS techniques in aerosol research have expanded remarkably as evident by skyrocketing publication statistics. The goal of this review is to present the most recent developments in the field of aerosol mass spectrometry for the time period of late 2010 to early 2012, which have not been conveyed in previous reviews.

Particle chemical properties in the vertical column based on aircraft observations in the vicinity of Cape Verde Islands

Particle chemical properties in the vertical column based on aircraft observations in the vicinity of Cape Verde Islands

More Effective Nanomedicines through Particle Design

Nanomedicine is an emerging field that applies concepts in nanotechnology to develop novel diagnostics and therapies. Physical and chemical properties of particles, including size, shape, modulus, surface charge and surface chemistry, play an important role in determining particle-cell interactions, cellular trafficking mechanisms, biodistribution, and pharmacokinetics. This discussion focuses on both nanoparticles and microparticles since microparticles can also provide many insights for the development of drug carriers and possess advantages over nanoparticles in certain applications. This review covers recent major advancement in the nanomedicine field and also highlights studies using the PRINT technology.

Physicochemical Characterization of Particulate Emissions from a Compression Ignition Engine Employing Two Injection Technologies and Three Fuels

Alternative fuels and injection technologies are a necessary component of particulate emission reduction strategies for compression ignition engines. Consequently, this study undertakes a physicochemical characterization of diesel particulate matter (DPM) for engines equipped with alternative injection technologies (direct injection and common rail) and alternative fuels (ultra low sulfur diesel, a 20% biodiesel blend, and a synthetic diesel). Particle physical properties were addressed by measuring particle number size distributions, and particle chemical properties were addressed by measuring polycyclic aromatic hydrocarbons (PAHs) and reactive oxygen species (ROS). Particle volatility was determined by passing the polydisperse size distribution through a thermodenuder set to 300 °C. The results from this study, conducted over a four point test cycle, showed that both fuel type and injection technology have an impact on particle emissions, but injection technology was the more important factor. Significant particle number emission (54%-84%) reductions were achieved at half load operation (1% increase-43% decrease at full load) with the common rail injection system; however, the particles had a significantly higher PAH fraction (by a factor of 2 to 4) and ROS concentrations (by a factor of 6 to 16) both expressed on a test-cycle averaged basis. The results of this study have significant implications for the health effects of DPM emissions from both direct injection and common rail engines utilizing various alternative fuels.

Particle chemical properties in the vertical column based on aircraft observations in the vicinity of Cape Verde Islands

During the second Saharan Mineral Dust Experiment (SAMUM-2) field campaign, particles with geometric diameters (d) between ∼0.1 and 25 μm were collected on board of the Deutsches Zentrum f¨ur Luft- und Raumfahrt (German Aerospace Center, DLR) Falcon aircraft. Size, chemical composition and mixing state of aerosols sampled (spatially and vertically resolved) along theWest African coastline and in the Cape Verde Islands region were determined by electron microscopy. A pronounced layer structure of biomass-burning aerosol and desert dust was present for all days during the sampling period from 23 January to 6 February. The aerosol composition of the small particles (d < 0.5 μm) was highly variable and in cases of biomass burning strongly dominated by soot with up to 90% relative number abundance. Internal mixtures of soot particles with mineral dust were not detected. Soot was only observed to mix with secondary sulphate. The coarse particles (d > 0.5 μm) were dominated by silicates. In the Cape Verde Islands region mineral dust is well mixed. The determination of source regions by elemental or mineralogical composition was generally not possible, except for air masses which were transported over the Gulf of Guinea. The real part of the refractive index showed little variation. In contrast, the imaginary part strongly depended on the abundance of soot (biomass-burning aerosol) and haematite (mineral dust).

Fast and Efficient Method for Fire Detection Using Image Processing

Conventional fire detection systems use physical sensors to detect fire. Chemical properties of particles in the air are acquired by sensors and are used by conventional fire detection systems to raise an alarm. However, this can also cause false alarms; for example, a person smoking in a room may trigger a typical fire alarm system. In order to manage false alarms of conventional fire detection systems, a computer vision-based fire detection algorithm is proposed in this paper. The proposed fire detection algorithm consists of two main parts: fire color modeling and motion detection. The algorithm can be used in parallel with conventional fire detection systems to reduce false alarms. It can also be deployed as a stand-alone system to detect fire by using video frames acquired through a video acquisition device. A novel fire color model is developed in CIE L*a*b* color space to identify fire pixels. The proposed fire color model is tested with ten diverse video sequences including different types of fire. The experimental results are quite encouraging in terms of correctly classifying fire pixels according to color information only. The overall fire detection system's performance is tested over a benchmark fire video database, and its performance is compared with the state-of-the-art fire detection method.

Fabrication of poly(ethylene glycol) hydrogel structures for pharmaceutical applications using electron beam and optical lithography

Soft-polymer based microparticles are currently being applied in many biomedical applications, ranging from bioimaging and bioassays to drug delivery carriers. As one class of soft-polymers, hydrogels are materials, which can be used for delivering drug cargoes and can be fabricated in controlled sizes. Among the various hydrogel-forming polymers, poly(ethylene glycol) (PEG) based hydrogel systems are widely used due to their negligible toxicity and limited immunogenic recognition. Physical and chemical properties of particles (i.e., particle size, shape, surface charge, and hydrophobicity) are known to play an important role in cell-particle recognition and response. To understand the role of physicochemical properties of PEG-based hydrogel structures on cells, it is important to have geometrically precise and uniform hydrogel structures. To fabricate geometrically uniform structures, we have employed electron beam lithography (EBL) and ultra-violet optical lithography (UVL) using PEG or PEG diacrylate polymers. These hydrogel structures have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy, and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirming control of chemistry, size, and shape.

Chemistry, Mechanics and the Making of Anatomical Knowledge: Boerhaave vs. Ruysch on the Nature of the Glands

A controversy between the well-known medical teacher Herman Boerhaave and the anatomist Frederik Ruysch on the nature of the glands shows how chemical knowledge had a decisive influence on the way in which Boerhaave perceived the anatomy and working of the glands. While Ruysch maintained that the glands are no more than the extremities of arteries and act as mechanical instruments separating the fluids into smaller particles, Boerhaave examined the glands as membranous follicles in which chemical processes prepare the fluids for their different uses in the body. Boerhaave, in other words, turned to the chemical properties of particles rather than the vessels that contain them. Boerhaave's viewpoint was new and resulted from his belief in chemistry as the discipline par excellence for the explanation of the most basic processes in the body. More than anything else, the controversy shows how chemistry was not contained within fixed disciplinary boundaries, but had a decisive influence on Boerhaave's construction of anatomical knowledge.

Source-Specific Fine Particles in Urban Air and Respiratory Function Among Adult Asthmatics

Fine and ultrafine particles in ambient air are more consistently associated with severe adverse health effects than coarse particles. We assessed whether the effects of PM2.5 on peak expiratory flow (PEF) and respiratory symptoms in asthma patients differ by the source or the chemical properties of particles. A panel of 57 adult asthmatics was followed for 181 days from November 1996 to April 1997 with 3 daily PEF measurements and diaries. Air quality, including elemental analyses of PM2.5 filters every 2 days (n = 83), was monitored at a central site. Daily concentrations of PM2.5 from different sources were estimated using principal component analysis and multiple linear regression. Associations of PM2.5 from different sources with respiratory endpoints were examined using a generalized least squares autoregressive model after adjustment for covariates. PM2.5 attributable to local combustion was consistently negatively associated with all measurements of PEF. One interquartile increase (1.3 μ g/m3) in 5-day average concentrations of PM2.5 attributable to local combustion was associated with an average 1.14 L/min decline in evening PEF (95% CI: −1.95 to −0.33 L/min). We also observed that PM2.5 attributable to long-range transport was positively, and soil-derived PM2.5 negatively, associated with PEF. No consistent associations were observed between source-specific PM2.5 and respiratory symptoms or between individual chemical elements and any respiratory endpoints. Our results suggest that the negative effects of PM2.5 on PEF in adult asthmatics are mainly mediated by particles related to local combustion sources.

Synchrotron radiation induced μ-X-ray fluorescence spectroscopy on municipal solid waste fly ashes

The high brightness of synchrotron radiation sources of the 3rd generation and the development of focusing optical elements for X-rays make it possible to create beams of micrometer size with high intensity. These beams can be used to reveal spatially resolved information about structural and chemical properties of particles. Here, the possibility of using synchrotron radiation micro-X-ray fluorescence (μ-SRXRF) for the determination of the major and minor components and their distribution within municipal solid waste (MSW) fly ashes has been investigated. By using an excitation energy of 27.0 keV, trace elements of environmental concern, like Cd, Pb and Zn can be detected to their low concentrations (ppm) routinely. The aim of the work was to gain a better understanding of the factors that determine the environmental mobility of each trace element and, in particular, the potential for their dissolution and leaching. Such detailed investigation of the content and distribution of toxic metals on/in individual particles is a valuable complement to the usual elemental analysis of bulk samples.

Hydrolysis of phosphatidylcholine by hepatic lipase in discoidal and spheroidal recombinant high-density lipoprotein.

Hepatic lipase (HL) hydrolysis of phosphatidylcholine (PC) was studied in recombinant high-density lipoprotein particles (r-HDL). r-HDL were made from cholate mixed micelles that contained PC, apo AI, and, in some cases, unesterified cholesterol. r-HDL were characterized using chemical composition, nondenaturing gradient gel electrophoresis, transmission electron microscopy, and dynamic light scattering. The r-HDL were found to be discoidal and in the size range of native HDL. Upon treatment of cholesterol-containing r-HDL with lecithin-cholesterol acyltransferase (LCAT), to form cholesteryl ester, the discoidal r-HDL became spheroidal. The effects of r-HDL morphology and size on HL activity were studied on r-HDL made of palmitoyloleoyl-PC, unesterified cholesterol, cholesteryl ester, and apolipoprotein AI. Spheroidal r-HDL were hydrolyzed at a faster rate than discoidal r-HDL. Protein-poor r-HDL were hydrolyzed by HL at a faster rate than protein rich r-HDL. Unesterified cholesterol had no apparent effect on particle PC hydrolysis. The hydrolysis of different species of PC [dipalmitoyl (DPPC), dioleoyl(DOPC), palmitoylarachidonoyl (PAPC), and palmitoyloleoyl (POPC)] in r-HDL was also investigated. In discoidal r-HDL, we found that POPC >/= DOPC = PAPC/DPPC. However, in LCAT-treated spheroidal r-HDL, POPC = DOPC > PAPC/DPPC. In both discoidal and spheroidal rHDL, DPPC containing r-HDL were not hydrolyzed to a significant extent. Collectively, these studies demonstrate that the physico-chemical properties of particles (such as phospholipid packing and phospholipid acyl composition) play a significant role in hydrolysis of HDL phospholipid by HL and, therefore, in reverse cholesterol transport.

On the distribution of physical and chemical particle properties in the atmospheric aerosol

Consideration of sources and growth dynamics of aerosols has led to the conclusion that there may be a distribution or variation of chemical composition and physical structure among atmospheric aerosol particles as a function of size, and within a narrow size range as well. A mathematical representation of these particle properties in terms of an additional dimension to the number size distribution is described. Examples of the relevance of this aspect of aerosol characterization for physical and chemical processes in the atmosphere are discussed. A review of the available techniques shows that several methods are available which can and have provided quantitative results on the distribution of particle properties. Examples of data from the literature have been selected and are presented as three-dimensional distributions illustrating the wide range of particle properties which may exist in narrow size intervals. An evaluation of these results reiterates the value of taking the distribution of particle properties in the atmosphere into account for sampling and modeling purposes.

Comparison of particles in the fume from eruptions of Kilauea, Mayon, and Arenal volcanoes

The physical and chemical properties of particles collected from the eruption fume of Kilauea, Mayon, and Arenal volcanoes were determined by colorimetric chemical techniques, neutron activation, atomic absorption, X-ray diffraction, an electron microprobe, and electron microscopy. As in previous studies, more than 95% of the Kilauea particles were largely dilute sulfuric acid droplets plus some mainly needle-like crystals, which previously had been tentatively identified as sulfur and calcium and ammonium sulfates. The wet chemical analysis demonstrated the presence of soluble calcium, ammonium, and magnesium sulfates. Each type of particle observed at Kilauea was also observed at Mayon, but most of the droplets from Mayon were much less acidic. Some Mayon particles were ‘ash’ or minute spheres; this type of particle was not observed at Kilauea. Particles in the fume from Arenal were more like the particles from Mayon than like those from Kilauea.