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Atmospheric tar balls (TBs) are spherical, organic aerosol particles that occur in smoke from biomass burning (BB). They absorb sunlight and thereby cause warming of the atmosphere. This study reports a transmission electron microscope (TEM) study of TBs from BB smoke samples collected within minutes to hours from emission in a tropical area of Mexico. Their spherical shapes as seen in both scanning electron microscope images and with electron tomography indicate that they were solid when collected. They consist of C and minor O, S, K, and N. The hygroscopic growth factor for our relatively fresh TBs is 1.09 ± 0.04 at a relative humidity of 100%. In samples <0.6 km and >1.6 km from the fire, an average of ∼1 and 14%, respectively, of particles with aerodynamic diameter from 50 to 300 nm consisted of TBs. For the latter, more aged samples, the total volume was roughly double that of soot, and their total calculated light absorption at a wavelength of 550 nm was between 74 and 96% that of soot, with the exact amount depending on the size, shape, and coating of the soot. In general, the TBs that we analyzed were similar to those from North America, southern Africa, and Europe in terms of size, external mixing, relative freedom of inclusions, and composition. This and previous studies show that TBs result from a range of biomass fuels. Their distribution from various regions across the globe, combined with their optical properties, suggests they have important effects on regional and perhaps global climate.

Biomass burning (BB) emits enormous amounts of aerosol particles and gases into the atmosphere and thereby significantly influences regional air quality and global climate. A dominant particle type from BB is spherical organic aerosol particles commonly referred to as tarballs. Currently, tarballs can only be identified, using microscopy, from their uniquely spherical shapes following impaction onto a grid. Despite their abundance and potential significance for climate, many unanswered questions related to their formation, emission inventory, removal processes, and optical properties still remain. Here, we report analysis that supports tarball formation in which primary organic particles undergo chemical and physical processing within ∼3 h of emission. Transmission electron microscopy analysis reveals that the number fractions of tarballs and the ratios of N and O relative to K, the latter a conserved tracer, increase with particle age and that the more-spherical particles on the substrates had higher ratios of N and O relative to K. Scanning transmission X-ray spectrometry and electron energy loss spectrometry analyses show that these chemical changes are accompanied by the formation of organic compounds that contain nitrogen and carboxylic acid. The results imply that the chemical changes increase the particle sphericity on the substrates, which correlates with particle surface tension and viscosity, and contribute to tarball formation during aging in BB smoke. These findings will enable models to better partition tarball contributions to BB radiative forcing and, in so doing, better help constrain radiative forcing models of BB events.

Carbyne-related materials permit exploring the potentially extraordinary properties of this long-sought but still elusive carbon allotrope. However, accurate understanding of these materials is challenging. Here we report the crystal structure of a Au-pseudocarbyne, a representative of a possible new family of materials consisting of sp -hybridized carbon chains and stabilizing metal atoms. Au-pseudocarbyne(C 6 ), the representative pseudocarbyne containing six-membered carbon chains, has space group P6/mmm 191 and unit-cell parameters a  =  b  = 0.60 nm, c  = 0.896 nm, α  =  β  = 90°, γ  = 120°. Its long-range structure can be understood as intimately intergrown bundles, each consisting of six parallel, infinite carbon chains surrounding a column of gold atoms. This compound, together with its eight-membered counterpart Au-pseudocarbyne(C 8 ), shows that interesting new materials resembling the carbyne structure and sharing some of its properties can be designed and developed. The current work raises serious questions regarding recent reports of carbyne synthesis.

The Amazon basin is important for understanding the global climate because of its carbon cycle and as a laboratory for obtaining basic knowledge of the continental background atmosphere. Aerosol particles play an important role in the climate and weather, and knowledge of their compositions and mixing states is necessary to understand their influence on the climate. For this study, we collected aerosol particles from the Amazon basin during the Green Ocean Amazon (GoAmazon2014/5) campaign (February to March 2014) at the T3 site, which is located about 70 km from Manaus, and analyzed them using transmission electron microscopy (TEM). TEM has better spatial resolution than other instruments, which enables us to analyze the occurrences of components that attach to or are embedded within other particles. Based on the TEM results of more than 10 000 particles from several transport events, this study shows the occurrences of individual particles including compositions, size distributions, number fractions, and possible sources of materials that mix with other particles. Aerosol particles during the wet season were from both natural sources such as the Amazon forest, Saharan desert, Atlantic Ocean, and African biomass burning and anthropogenic sources such as Manaus and local emissions. These particles mix together at an individual particle scale. The number fractions of mineral dust and sea-salt particles increased almost 3-fold when long-range transport (LRT) from the African continent occurred. Nearly 20 % of mineral dust and primary biological aerosol particles had attached sea salts on their surfaces. Sulfates were also internally mixed with sea-salt and mineral dust particles. The TEM element mapping images showed that several components with sizes of hundreds of nanometers from different sources commonly occur within individual LRT aerosol particles. We conclude that many aerosol particles from natural sources change their compositions by mixing during transport. The compositions and mixing states of these particles after emission result in changes in their hygroscopic and optical properties and should be considered when assessing their effects on climate.

Internally mixed aerosol particles consisting of one or more hygroscopic compounds can contain both solid and liquid parts, the details depending on the relative humidity (RH). The solid‐to‐liquid transition of such particles as the RH increases influences their light‐scattering properties through changes in particle shape, size, and refractive index. Most techniques used to analyze ambient aerosol particles do not have the ability to view both solid and liquid phases within individual particles. Using a transmission electron microscope fitted with an environmental cell (ETEM), we analyzed laboratory‐prepared and ambient aerosol samples. Our results suggest that solid inclusions inside aqueous droplets at high RH values (e.g., >65%) are likely to be common in atmospheric particles. In order to assess the effects of such inclusions, we calculated their combined light‐scattering efficiencies using a discrete dipole approximation (DDA). The results show differences compared to those from a core‐shell model, with an average increase in light scattering of ∼20%. The results demonstrate that the combination of ETEM measurements of ambient particles with DDA calculations yields new insights into the effects of inclusions on the light‐scattering properties of internally mixed particles.

Soot aerosol particles (also called light‐absorbing, black, or elemental carbon) are major contributors to global warming through their absorption of solar radiation. When embedded in organic matter or sulfate, as is common in polluted areas such as over Mexico City (MC) and other megacities, their optical properties are affected by their shapes and positions within their host particles. However, large uncertainties remain regarding those variables and how they affect warming by soot. Using electron tomography with a transmission electron microscope, three‐dimensional (3‐D) images of individual soot particles embedded within host particles collected from MC and its surroundings were obtained. From those 3‐D images, we calculated the optical properties using a discrete dipole approximation. Many soot particles have open, chainlike shapes even after being surrounded by organic matter and are located in off‐center positions within their host materials. Such embedded soot absorbs sunlight less efficiently than if compact and located near the center of its host particle. In the case of our MC samples, their contribution to direct radiative forcing is ∼20% less than if they had a simple core‐shell shape, which is the shape assumed in many climate models. This study shows that the shapes and positions of soot within its host particles have an important effect on particle optical properties and should be recognized as potentially important variables when evaluating global climate change.

Aerosol particles are ubiquitous in the troposphere and exert an important influence on global climate and the environment. They affect climate through scattering, transmission, and absorption of radiation as well as by acting as nuclei for cloud formation. A significant fraction of the aerosol particle burden consists of minerals, and most of the remainder--whether natural or anthropogenic--consists of materials that can be studied by the same methods as are used for fine-grained minerals. Our emphasis is on the study and character of the individual particles. Sulfate particles are the main cooling agents among aerosols; we found that in the remote oceanic atmosphere a significant fraction is aggregated with soot, a material that can diminish the cooling effect of sulfate. Our results suggest oxidization of SO2may have occurred on soot surfaces, implying that even in the remote marine troposphere soot provided nuclei for heterogeneous sulfate formation. Sea salt is the dominant aerosol species (by mass) above the oceans. In addition to being important light scatterers and contributors to cloud condensation nuclei, sea-salt particles also provide large surface areas for heterogeneous atmospheric reactions. Minerals comprise the dominant mass fraction of the atmospheric aerosol burden. As all geologists know, they are a highly heterogeneous mixture. However, among atmospheric scientists they are commonly treated as a fairly uniform group, and one whose interaction with radiation is widely assumed to be unpredictable. Given their abundances, large total surface areas, and reactivities, their role in influencing climate will require increased attention as climate models are refined.

Lonsdaleite, also called hexagonal diamond, has been widely used as a marker of asteroidal impacts. It is thought to play a central role during the graphite-to-diamond transformation, and calculations suggest that it possesses mechanical properties superior to diamond. However, despite extensive efforts, lonsdaleite has never been produced or described as a separate, pure material. Here we show that defects in cubic diamond provide an explanation for the characteristic d -spacings and reflections reported for lonsdaleite. Ultrahigh-resolution electron microscope images demonstrate that samples displaying features attributed to lonsdaleite consist of cubic diamond dominated by extensive {113} twins and {111} stacking faults. These defects give rise to nanometre-scale structural complexity. Our findings question the existence of lonsdaleite and point to the need for re-evaluating the interpretations of many lonsdaleite-related fundamental and applied studies. Lonsdaleite has been used as a marker of asteroid impacts and is thought to have mechanical properties superior to diamond; however, pure lonsdaleite has not been described or fabricated. Here, the authors show that it does not exist as a discrete material and is in fact faulted and twinned cubic diamond.

Biomass burning is a major source of light-absorbing black and brown carbonaceous particles. Tar balls (TBs) are a type of brown carbonaceous particle apparently unique to biomass burning. Here we describe the first atmospheric observations of the formation and evolution of TBs from forest fires. Aerosol particles were collected on transmission electron microscopy (TEM) grids during aircraft transects at various downwind distances from the Colockum Tarps wildland fire. TB mass fractions, derived from TEM and in situ measurements, increased from <1 % near the fire to 31–45 % downwind, with little change in TB diameter. Given the observed evolution of TBs, it is recommended that these particles be labeled as processed primary particles, thereby distinguishing TB formation–evolution from secondary organic aerosols. Single-scattering albedo determined from scattering and absorption measurements increased slightly with downwind distance. Similar TEM and single-scattering albedo results were observed sampling multiple wildfires. Mie calculations are consistent with weak light absorbance by TBs (i.e., m similar to the literature values 1.56−0.02i or 1.80−0.007i) but not consistent with absorption 1 order of magnitude stronger observed in different settings. The field-derived TB mass fractions reported here indicate that this particle type should be accounted for in biomass burning emission inventories.