Mihály Pósfai

Individual aerosol particles from biomass burning in southern Africa: 1. Compositions and size distributions of carbonaceous particles

[1] Individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging. Based on composition, morphology, and microstructure, three distinct types of carbonaceous particles were present in the smoke: organic particles with inorganic (K-salt) inclusions, ‘‘tar ball’’ particles, and soot. The relative number concentrations of organic particles were largest in young smoke, whereas tar balls were dominant in a slightly aged (1 hour) smoke from a smoldering fire. Flaming fires emitted relatively more soot particles than smoldering fires, but soot was a minor constituent of all studied plumes. Further aging caused the accumulation of sulfate on organic and soot particles, as indicated by the large number of internally mixed organic/sulfate and soot/sulfate particles in the regional haze. Externally mixed ammonium sulfate particles dominated in the boundary layer hazes, whereas organic/sulfate particles were the most abundant type in the upper hazes. Apparently, elevated haze layers were more strongly affected by biomass smoke than those within the boundary layer. Based on size distributions and the observed patterns of internal mixing, we hypothesize that organic and soot particles are the cloudnucleating constituents of biomass smoke aerosols. Sea-salt particles dominated in the samples taken in stratus clouds over the Atlantic Ocean, off the coast of Namibia, whereas a distinct haze layer above the clouds consisted of aged biomass smoke particles. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: biomass burning, carbonaceous aerosol, individual particles, TEM

Influence of sea-salt on aerosol radiative properties in the Southern Ocean marine boundary layer

There has been considerable debate about the relative importance of sea-salt and sulphate from non-sea-salt sources in determining aerosol radiative effects in the marine boundary layer. In the marine boundary layer, the most numerous aerosols are volatile sulphate particles smaller than about 0.08 µm (ref. 1) and most of the aerosol mass is in a few sea-salt particles larger than 1 µm. Yet intermediate-size aerosols between about 0.08 and 1 µm diameter are the most relevant to the radiative forcing of climate because they efficiently scatter solar radiation and also serve as cloud nuclei. Indeed, Charlson et al. hypothesized that oceanic production of sulphate aerosols from the oxidation of dimethyl sulphide could be a powerful feedback in the climate system. It is generally assumed that marine aerosols smaller than about 1 µm are non-sea-salt sulphate, but a recent review cites indirect evidence that many aerosols in the sub-micrometre range contain at least some sea-salt,. Here we present direct observational evidence from a remote Southern Ocean region that almost all aerosols larger than 0.13 µm in the marine boundary layer contained sea-salt. These sea-salt aerosols had important radiative effects: they were responsible for the majority of aerosol-scattered light, and comprised a significant fraction of the inferred cloud nuclei.

Soot and sulfate aerosol particles in the remote marine troposphere

Sulfate aerosol particles containing soot aggregates were observed in the marine troposphere in both hemispheres under conditions that ranged from extremely clean to heavily polluted. Even in clean air above the remote Southern Ocean during the First Aerosol Characterization Experiment (ACE 1), depending on the sample, between 10 and 45% of sulfate particles contained soot inclusions. We identified aircraft emissions and biomass burning as the most likely major sources of soot. Internally mixed soot and sulfate appear to comprise a globally significant fraction of aerosols in the troposphere. Anthropogenic combustion aerosols can thus potentially change the radiative climate effects of sulfate aerosols and may have an impact on cloud properties even in the remote troposphere.

Magnetite morphology and life on Mars

Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from the Martian meteorite. In contrast to previous accounts, we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars.

A Cultured Greigite-Producing Magnetotactic Bacterium in a Novel Group of Sulfate-Reducing Bacteria

The crystal structure of biomineralized magnetic nanocrystals depends on environmental and genetic factors. Magnetotactic bacteria contain magnetosomes—intracellular, membrane-bounded, magnetic nanocrystals of magnetite (Fe3O4) or greigite (Fe3S4)—that cause the bacteria to swim along geomagnetic field lines. We isolated a greigite-producing magnetotactic bacterium from a brackish spring in Death Valley National Park, California, USA, strain BW-1, that is able to biomineralize greigite and magnetite depending on culture conditions. A phylogenetic comparison of BW-1 and similar uncultured greigite- and/or magnetite-producing magnetotactic bacteria from freshwater to hypersaline habitats shows that these organisms represent a previously unknown group of sulfate-reducing bacteria in the Deltaproteobacteria. Genomic analysis of BW-1 reveals the presence of two different magnetosome gene clusters, suggesting that one may be responsible for greigite biomineralization and the other for magnetite.

Compositional variations of sea-salt-mode aerosol particles from the North Atlantic

Individual sea-salt-mode aerosol particles collected during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) experiment in June 1992 were studied using transmission electron microscopy in both imaging and analysis modes. The set of eight samples provided an opportunity to compare “clean,” “intermediate,” and “dirty” oceanic aerosols. In the clean samples, major species include NaCl, mixed-cation (Na, Mg, K, and Ca) sulfates, and in some particles, NaNO3. The same compounds also occur in intermediate samples, but compositional groups can be distinguished that are characterized by low- and high-Cl losses from sea salt. In these samples, most Cl loss is compensated by NaNO3 formation. Several compositional groups occur in the dirty samples; these include, in addition to the particle types in clean and intermediate samples, Na2SO4 (with minor Mg, K, and Ca), (NH4)2SO4, and silicates. The uniform compositions of sea-salt-mode particles in the clean samples suggest that the same process was acting on all particles. Their excess sulfate and nitrate probably formed through the oxidation of SO2 in the sea-salt aerosol water and by reactions between NOx and NaCl. On the other hand, distinct compositional groups in the dirty samples reveal that long-range transport of continental air masses resulted in the mixing of aerosols that were exposed to different conditions. In addition to O3 oxidation, cloud processing may have contributed to the formation of excess sulfate in these samples.

The Red Mud Accident in Ajka (Hungary): Characterization and Potential Health Effects of Fugitive Dust

As a result of a tragic industrial accident, a highly alkaline red mud sludge inundated settlements and agricultural areas near Ajka, Hungary on October 4, 2010. One of the major concerns about the aftermaths of the accident is the potential health effects of vast amounts of fugitive dust from red mud sediment. Thus, we studied the chemical and physical properties of particles of red mud and its respirable fugitive dust, and performed toxicity measurements. Under unfavorable meteorological conditions dry red mud sediment could emit very high amounts of respirable alkaline particles into the air. The number size distribution of fugitive dust peaks above 1 μm aerodynamic diameter; therefore, its inhalation is unlikely to affect the deep regions of the lungs. No significant mineralogical or elemental fractionation was observed between the sediment and dust, with the major minerals being hematite, cancrinite, calcite, and hydrogarnet. Although the high resuspension potential and alkalinity might pose some problems such as the irritation of the upper respiratory tract and eyes, based on its size distribution and composition red mud dust appears to be less hazardous to human health than urban particulate matter.

Wet and dry sizes of atmospheric aerosol particles: An AFM‐TEM Study

We studied the hygroscopic behavior of atmospheric aerosols by using a novel approach, the combination of atomic force microscopy (AFM) with transmission electron microscopy (TEM) imaging of the same individual particles. By comparing the dimensions of hydrated and dry ammonium sulfate particles collected above the North Atlantic Ocean, we determined that particle volumes are up to four times larger under ambient conditions (as determined by AFM) than in the vacuum of a transmission electron microscope. We interpret these changes as resulting from the loss of water. Organic films on the particles may be responsible for the relatively large water uptake at low relative humidities.

Biosynthesis of magnetic nanostructures in a foreign organism by transfer of bacterial magnetosome gene clusters

The synthetic production of monodisperse single magnetic domain nanoparticles at ambient temperature is challenging. In nature, magnetosomes--membrane-bound magnetic nanocrystals with unprecedented magnetic properties--can be biomineralized by magnetotactic bacteria. However, these microbes are difficult to handle. Expression of the underlying biosynthetic pathway from these fastidious microorganisms within other organisms could therefore greatly expand their nanotechnological and biomedical applications. So far, this has been hindered by the structural and genetic complexity of the magnetosome organelle and insufficient knowledge of the biosynthetic functions involved. Here, we show that the ability to biomineralize highly ordered magnetic nanostructures can be transferred to a foreign recipient. Expression of a minimal set of genes from the magnetotactic bacterium Magnetospirillum gryphiswaldense resulted in magnetosome biosynthesis within the photosynthetic model organism Rhodospirillum rubrum. Our findings will enable the sustainable production of tailored magnetic nanostructures in biotechnologically relevant hosts and represent a step towards the endogenous magnetization of various organisms by synthetic biology.

Three-Dimensional Tomographic Imaging and Characterization of Iron Compounds within Alzheimer's Plaque Core Material

Although it has been known for over 50 years that abnormal concentrations of iron are associated with virtually all neurodegenerative diseases, including Alzheimers disease, its origin, nature and role have remained a mystery. Here, we use high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) spectroscopy and electron energy-loss spectroscopy (EELS), electron tomography, and electron diffraction to image and characterize iron-rich plaque core material - a hallmark of Alzheimers disease pathology - in three dimensions. In these cores, we unequivocally identify biogenic magnetite and/or maghemite as the dominant iron compound. Our results provide an indication that abnormal iron biomineralization processes are likely occurring within the plaque or the surrounding diseased tissue and may play a role in aberrant peptide aggregation. The size distribution of the magnetite cores implies formation from a ferritin precursor, implicating a malfunction of the primary iron storage protein in the brain.