Giant Particles Research Articles

Multi-scale characterization of lead-rich deposited particles originating from the fire of Notre-Dame de Paris

Fire is a major hazard for built heritage. The fire at Notre-Dame on April 15, 2019 completely destroyed the woodframe and the lead roof (about 285 tons) almost entirely melted due to high temperatures. A part of the molten lead escaped into the atmosphere in the form of aerosols while the majority remains within cathedral enclosure in the form of deposits, metallic remains, spatters etc. In particular unusual yellowish deposits of lead-rich particles were observed and collected inside the monument (in the nave, near the organ and in St-Eloi Chapel). These were then thoroughly characterized to identify the neoformed lead compounds. Both bulk and local analyses were carried out to obtain particle morphology and size distribution, chemistry and mineralogy of the deposits, from macro to nanoscale. We found that the fire-related deposits all contain high amount of lead (10 to 44 %) mainly in the form of monoxides (litharge and massicot) with other lead-bearing phases (Ca-plumbate, metallic lead, lead sulfates and carbonates, plattnerite) in smaller amount. These lead phases are concentrated in heterogeneous microspheres, at the periphery of terrigenous minerals (calcite, quartz, feldspars) or mixed with anhydrite minerals. The size distribution shows that the fire produced giant particles (> 100 μm in diameter) similar to those found near the fallout from industrial emissions. This study provides a better understanding of the lead contamination pathways following the Notre-Dame cathedral fire and new insights into the reactivity of lead during a fire.

High-resolution sampling in the eastern tropical North Atlantic reveals episodic Saharan dust deposition: implications for the marine carbon sink

In this study we present data collected between August 2017 and December 2018 from submarine sediment trap M1 located in the eastern tropical North Atlantic and determine lithogenic and biogenic fluxes, and grain-size distributions of aerosol dust. An unprecedented high sampling resolution of four days in combination with satellite imagery allowed the identification of thirteen major dust events of two types within the 468-day series. Seven dust events were classified as high-flux events identified by a deposition of >=25 mg m-2 d-1. The average dust deposition rate increased by 461.3% during these types of events. The remaining six events were characterized by a high composition of giant particles (>7.3 vol%). Seasonal variations of dust flux were recorded, with highest fluxes observed in spring at an average deposition rate of 14.8 mg m-2 d-1, and lowest fluxes in fall with an average rate of 8.6 mg m-2 d-1. The estimated total dust flux in the tropical North Atlantic was 4040.02 mg m-2 y-1. We suggest that most of the summer dust was likely transported over the sampling site at high altitudes while winter transport occurred closer to the sea surface, resulting in generally higher background fluxes. Grain-size distributions exhibited seasonal variations with increased occurrences of giant particles (>62.5 μm) in fall 2017 and spring, and less occurrences in winter and fall 2018. Grain-size sorting was high in spring and most variable in summer. Precipitation did not affect depositional fluxes or grain-size distributions of the aeolian dust significantly. Organic matter was deposited continuously at the sampling site with a deposition rate ranging from 14.4–862.25 mg m-2 d-1. Organic matter fluxes increased by 199.5% during high-flux dust events but decreased by 13.6% during anomalous grain-size events. Spring experienced the highest number of dust events (n=5). This unprecedented high-resolution dataset of dust deposition in marine sediment-traps enabled the distinction of dust events and their relation to organic matter flux. This suggests the possibility of a dust fertilization or mineral ballasting effect.

A prediction model of maximum dry density of over coarse-grained soil

The control of maximum dry density is an important issue for over coarse-grained soil. A theoretical formula of the maximum dry density for over coarse-grained soil was derived, which is related to the maximum dry density of the original soil, particle density, and mass fraction of giant particles in the mixed soil. Maximum dry densities of seven groups of mixed soil were calculated by the discrete element method (DEM) and theoretical formula, and the results showed that the maximum dry densities obtained from the DEM were always lower than the results calculated by theoretical formula, and the difference increased with the increase in giant particle proportion. The volume growth coefficient was proposed to describe the increase in pore volume of the mixed soil caused by the embedding of giant particles, and the maximum dry density model for over coarse-grained soil was proposed. The results showed that the model fitted well to the DEM results, validating the high rationality and reliability.

Mechanisms controlling giant sea salt aerosol size distributions along a tropical orographic coastline

Abstract. Sea salt aerosol (SSA) is a naturally occurring phenomenon that arises from the breaking of waves and consequent bubble bursting on the ocean's surface. The resulting particles exhibit a bimodal distribution spanning orders of magnitude in size that introduces significant uncertainties when estimating the total annual mass of SSA on a global scale. Although estimates of mass and volume are significantly influenced by the presence of giant particles (dry radius >1 µm), effectively observing and quantifying these particles proves to be challenging. Additionally, uncertainties persist regarding the contribution of SSA production along coastlines, but preliminary studies suggest that coastal interactions may increase SSA particle concentrations by orders of magnitude. Moreover, our knowledge regarding the vertical distribution of SSA particles in the marine boundary layer remains limited, resulting in significant gaps in understanding the vertical mixing of giant aerosol particles and specific environmental conditions facilitating their dispersion. By addressing these uncertainties, particularly in regions where SSA particles constitute a substantial percentage of total aerosol loading, we can enhance our comprehension of the complex relationships between the air, sea, aerosols, and clouds. A case study conducted on the Hawaiian island of O`ahu offers insight into the influence of coastlines and orography on the production and vertical distribution of giant SSA size distributions. Along the coastline, the frequency of breaking waves is accelerated, serving as an additional source of SSA production. Furthermore, the steep island orography generates strong and consistent uplift under onshore trade wind conditions, facilitating vertical mixing of SSA particles along windward coastlines. To investigate this phenomenon, in situ measurements of SSA size distributions for particles with dry radii (rd) ≥ 2.8 µm were conducted for various altitudes, ranging from approximately 80 to 650 m altitude along the windward coastline and from 80 to 250 m altitude aboard a ship offshore. Comparing size distributions onshore and offshore confirmed significantly higher concentrations along the coastline, with 2.7–5.4 times greater concentrations than background open-ocean concentrations for supermicron particles. These size distributions were then analyzed in relation to environmental variables influencing SSA production and atmospheric dynamics. It was found that significant wave height exhibited the strongest correlation with changes in SSA size distributions. Additionally, simulated sea salt particle trajectories provided valuable insight into how production distance from the coastline impacts the horizontal and vertical advection of SSA particles of different sizes under varying trade wind speeds. Notably, smaller particles demonstrated reduced dependence on local wind speeds and production distance from the coastline, experiencing minimal dry deposition and high average maximum altitudes relative to larger particles. This research not only highlights the role of coastlines in enhancing the presence and vertical mixing potential of giant SSA particles, but also emphasizes how important it is to consider the influence of local factors on aerosol observations at different altitudes.

Dating recent tidal marsh sediments using windborne giant particles of green petcoke – An example from the southwest coast of Portugal

Coastal systems are especially vulnerable to human activities resulting from a range of direct physical modifications of the ecosystems to the biological, chemical, and physical impacts of pollutants. For the most recent decades, these modifications can be accurately tracked by industrial development indicators, providing an exceptional record of historical changes. In return, when such changes are identified in the sedimentological record, they can serve as precise chronological markers. Here, we examined the potential of petcoke particles, a by-product of crude oil refining, as an emergent sediment dating tool. To this end, giant (63–∼200 μm) black spheroidal petcoke particles – present in cores retrieved in the salt marshes of the Sado estuary (SW Portugal) – were used. These anthropogenic particles were counted and identified according to their morphology, structure, and chemical composition, using complementary micro-beam techniques: Scanning Electron Microscope and Energy Dispersive Spectroscopy, and Micro X-Ray Diffraction. The analyses revealed shot-type green petcoke particles containing a set of elements, which are well-known metallic/non-metallic impurities in petcoke. Based on the available historical data on petcoke imports in the port of Setúbal (Sado estuary) and Portugal, their first appearance in sediments can be dated to 1996 ± 2, with maxima in 2006 ± 4. Both the presence and the historical evolution of the use of petcoke in the region were recorded in all sediment cores, with higher particle density in locations aligned with the prevailing winds. The combination of petcoke and 137Cs data provided accretion rates for the 1963–2006 period ranging from 0.1 to 0.3 cm yr−1 (average: 0.2 cm yr−1), while these rates significantly increased from 2006 onwards (avg. rate: 1.1 cm yr−1; range: 0.6–2.1 cm yr−1). The widespread handling of petcoke worldwide leads us to suggest petcoke particles as a reliable chronological marker at local and regional scales, to be used in combination with other dating methods to build more exact sediment chronologies.

Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites.

Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100μm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94W m-1 K-1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. Our work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large-scale fabrication of vertical array with advanced functionalities. This article is protected by copyright. All rights reserved.

Modeling coarse and giant desert dust particles

Abstract. Dust particles larger than 20 µm in diameter have been regularly observed to remain airborne during long-range transport. In this work, we modify the parameterization of the mineral dust cycle in the GOCART-AFWA dust scheme of WRFV4.2.1 to also include such coarse and giant particles, and we further discuss the underlying misrepresented physical mechanisms which hamper the model in reproducing adequately the transport of the coarse and giant mineral particles. The initial particle size distribution is constrained by observations over desert dust sources. Furthermore, the Stokes drag coefficient has been updated to account for realistic dust particle sizes (Re < 105). The new code was applied to simulate dust transport over Cabo Verde in August 2015 (AER-D campaign). Model results are evaluated against airborne dust measurements and the CALIPSO-LIVAS pure dust product. The results show that the modeled lifetimes of the coarser particles are shorter than those observed. Several sensitivity runs are performed by reducing artificially the particles' settling velocities in order to compensate underrepresented mechanisms, such as the non-spherical aerodynamics, in the relevant parameterization schemes. Our simulations reveal that particles with diameters of 5.5–17 and 40–100 µm are better represented under the assumption of an 80 % reduction in the settling velocity (UR80), while particles with sizes ranging between 17 and 40 µm are better represented in a 60 % reduction in settling velocity (UR60) scenario. The overall statistical analysis indicates that the best agreement with airborne in situ measurements downwind (Cabo Verde) is achieved with a 40 % reduction in settling velocity (UR40). Moreover, the UR80 experiment improves the representation of the vertical structure of the dust layers as those are captured by the CALIPSO-LIVAS vertically resolved pure dust observations. The current study highlights the necessity of upgrading the existing model parameterization schemes of the dust life-cycle components towards improving the assessment of the dust-related impacts within the Earth–atmosphere system.

Identification and quantification of giant bioaerosol particles over the Amazon rainforest

Eukarya dominate the coarse primary biological aerosol (PBA) above the Amazon rainforest canopy, but their vertical profile and seasonality is currently unknown. In this study, the stratification of coarse and giant PBA >5 µm were analyzed from the canopy to 300 m height at the Amazon Tall Tower Observatory in Brazil during the wet and dry seasons. We show that >2/3 of the coarse PBA were canopy debris, fungal spores commonly found on decaying matter were second most abundant (ranging from 15 to 41%), followed by pollens (up to 5%). The atmospheric roughness layer right above the canopy had the greatest giant PBA abundance. Measurements over 5 years showed an increased abundance of PBA during a low-rainfall period. Giant particles, such as pollen, are reduced at 300 m, suggesting their limited dispersal. These results give insights into the giant PBA emissions of this tropical rainforest, and present a major step in understanding the type of emitted particles and their vertical distribution.

The Recent Relationships Between Andean Ice-Core Dust Record and Madeira River Suspended Sediments on the Wet Season

Dust particle studies in ice cores from the tropical Andes provide important information about climate dynamics. We investigated dust concentrations from a 22.7 m ice-core recovered from the Quelccaya Ice Cap (QIC) in 2018, representing 14 years of snow accumulation. The dust seasonality signal was still preserved with homogenization of the record due to surface melting and percolation. Using a microparticle counter, we measured the dust concentration from 2 to 60 µm and divided the annual dust concentration into three distinct groups: fine particle percentage (FPP, 2–10 µm), coarse particle percentage (CPP, 10–20 μm), and giant particle percentage (GPP, 20–60 μm). Increased dust was associated with the warm stage of the Pacific Decadal Oscillation index (PDO) after 2013 with significant increases in FPP and a relative decrease in CPP and GPP. There was a positive correlation between PDO and FPP (r = 0.70, p-value < 0.005). CPP and GPP were dominant during the mainly PDO cold phase (2003–2012). The FPP increase record occurs during the positive phase of PDO and snow accumulation decrease. We also revealed a potential link between QIC record and Madeira River during the wet season through two relationships: between QIC snow accumulation and runoff during transitional season, QIC dust, and suspended sediments during high-water discharge. The snow accumulation (during September-November) and runoff (during November-January) relationship present similar variability using a time-lag (60 days) while total dust and FPP group are associated with average suspended sediments concentration during February-April. Assessing dust record variability by distinct size groups can help to improve our knowledge of how the Pacific ocean influence dust record in the QIC. In addition, the association of snow accumulation and dust variability with dynamic changes in suspended sediments load and runoff in the Madeira River system demonstrates the potential for future investigation of linkages between QIC record and Amazon basin rivers.

Regulation of gene expression in <i>Nicotiana tabacum</i> seedlings by the MKASAA peptide through DNA methylation via the RdDM pathway

<abstract> <p>DNA methylation is involved in the protection of the genome, the regulation of gene expression, splicing, and is associated with a serious reprogramming of plant development. Using fluorescence microscopy, it was shown that the MKASAA peptide penetrates through the root system of <italic>Nicotiana tabacum</italic> tobacco, mainly into the cap, meristem, and elongation zones. In the cell, the peptide is localized mainly on the nuclei. In tobacco seedlings grown in the presence of the peptide at a concentration of 10<sup>–7</sup> M, an increase in the expression of DNA methyltransferases, especially DRM2, which methylates previously unmethylated DNA sites, is observed. In the presence of the peptide in the roots and leaves of tobacco, the level of global DNA methylation increases. An increase in DNA methylation occurs via the RdDM pathway. Presumably, the peptide binds to siRNAs, forming giant particles that remodulate chromatin and facilitate the entry of DNA methyltransferases. An increase in the level of DNA methylation is accompanied by silencing of the genes of the <italic>GRF</italic>, <italic>KNOX</italic>, and <italic>EXP</italic> families. Suppression of gene expression of these families is accompanied by significant morphological changes in tobacco seedlings. Thus, the short exogenous MKASAA peptide is involved in global morphological and genetic changes in tobacco seedlings.</p> </abstract>

Mineralogical, geochemical, and textural characteristics of soil and airborne samples during dust storms in Khuzestan, southwest Iran

Dust storms are frequent phenomena in Khuzestan Province, southwest Iran, leading to environmental hazards and deleterious impacts on human health. This work analyzes mineralogic and geochemical characteristics of dust sediments at the source regions and in deposition areas in southwest Iran during three dust-storm events in winter and spring 2018. Twenty soil and airborne dust samples were collected and analyzed for compositions of dust at different distances from the source regions in Iraq and southwest Iran, aiming to assess the source characterization and possible mixing processes in the atmosphere. The grain size distributions were also analyzed at specific sites. The results show that about 50 % of the volume size distribution corresponds to particle sizes of above 20 μm, indicating local/regional dust storms of coarse to giant particles. XRD analysis indicates that calcite is the dominant mineral in all the samples, with a high quartz and dolomite fraction. The most abundant major compounds are SiO2 and CaO, while Cl, Ba, Sr, Pb, Ni, Zn, Cr, V are the main trace elements. The enrichment factor (EF) analysis showed that apart from Th, Nb, Ce, and V, all the other elements (Pb, Zn, Cr, etc.) have an anthropogenic origin or represent high amounts of pollutant contamination. High levels of elemental enrichment are attributable to intensive pollution in Khuzestan Province and at sampling sites due to fossil-fuel combustion, gas and petroleum drilling activities. Moreover, based on the geo-accumulation index (Igeo), all samples are found to be contaminated by heavy metals due to prior war-related materiel, oil and gas extraction, and emissions from polluting industries.

Giant dust particles at Nevado Illimani: a proxy of summertime deep convection over the Bolivian Altiplano

Abstract. A deeper understanding of past atmospheric circulation variability in the Central Andes is a high-priority topic in paleoclimatology mainly because of the necessity to validate climate models used to predict future precipitation trends and to develop mitigation and/or adaptation strategies for future climate change scenarios in this region. Within this context, we here investigate an 18-year firn core drilled at Nevado Illimani in order to interpret its mineral dust record in relation to seasonal processes, in particular atmospheric circulation and deep convection. The core was dated by annual layer counting based on seasonal oscillations of dust, calcium, and stable isotopes. Geochemical and mineralogical data show that dust is regionally sourced in winter and summer. During austral summer (wet season), an increase in the relative proportion of giant dust particles (∅>20 µm) is observed, in association with oscillations of stable isotope records (δD, δ18O). It seems that at Nevado Illimani both the deposition of dust and the isotopic signature of precipitation are influenced by atmospheric deep convection, which is also related to the total amount of precipitation in the area. This hypothesis is corroborated by regional meteorological data. The interpretation of giant particle and stable isotope records suggests that downdrafts due to convective activity promote turbulent conditions capable of suspending giant particles in the vicinity of Nevado Illimani. Giant particles and stable isotopes, when considered together, can be therefore used as a new proxy for obtaining information about deep convective activity in the past.

The characterization of Taklamakan dust properties using a multiwavelength Raman polarization lidar in Kashi, China

Abstract. The Taklamakan desert is an important dust source for the global atmospheric dust budget and a cause of the dust weather in East Asia. The characterization of Taklamakan dust in the source region is still very limited. To fill this gap, the DAO (dust aerosol observation) was conducted in April 2019 in Kashi, China. The Kashi site is about 150 km from the western rim of the Taklamakan desert and is strongly impacted by desert dust aerosols, especially in spring time, i.e., April and May. According to sun–sky photometer measurements, the aerosol optical depth (at 500 nm) varied in the range of 0.07–4.70, and the Ångström exponent (between 440 and 870 nm) in the range of 0.0–0.8 in April 2019. In this study, we provide the first profiling of the 2α+3β+3δ parameters of Taklamakan dust based on a multiwavelength Mie–Raman polarization lidar. For Taklamakan dust, the Ångström exponent related to the extinction coefficient (EAE, between 355 and 532 nm) is about 0.01 ± 0.30, and the lidar ratio is found to be 45 ± 7 sr (51 ± 8–56 ± 8 sr) at 532 (355) nm. The particle linear depolarization ratios (PLDRs) are about 0.28–0.32 ± 0.07 at 355 nm, 0.36 ± 0.05 at 532 nm and 0.31 ± 0.05 at 1064 nm. Both lidar ratios and depolarization ratios are higher than the typical values of Central Asian dust in the literature. The difference is probably linked to the fact that observations in the DAO campaign were collected close to the dust source; therefore, there is a large fraction of coarse-mode and giant particles (radius >20 µm) in the Taklamakan dust. Apart from dust, fine particles coming from local anthropogenic emissions and long-range transported aerosols are also non-negligible aerosol components. The signatures of pollution emerge when dust concentration decreases. The polluted dust (defined by PLDR532≤0.30 and EAE355-532≥0.20) is featured with reduced PLDRs and enhanced EAE355−532 compared to Taklamakan dust. The mean PLDRs of polluted dust generally distributed in the range of 0.20–0.30. Due to the complexity of the nature of the involved pollutants and their mixing state with dust, the lidar ratios exhibit larger variabilities compared to those of dust. The study provides the first reference of novel characteristics of Taklamakan dust measured by Mie–Raman polarization lidar. The data could contribute to complementing the dust model and improving the accuracy of climate modeling.

Coarse and giant particles are ubiquitous in Saharan dust export regions and are radiatively significant over the Sahara

Abstract. Mineral dust is an important component of the climate system, interacting with radiation, clouds, and biogeochemical systems and impacting atmospheric circulation, air quality, aviation, and solar energy generation. These impacts are sensitive to dust particle size distribution (PSD), yet models struggle or even fail to represent coarse (diameter (d) >2.5 µm) and giant (d>20 µm) dust particles and the evolution of the PSD with transport. Here we examine three state-of-the-art airborne observational datasets, all of which measured the full size range of dust (d=0.1 to >100 µm) at different stages during transport with consistent instrumentation. We quantify the presence and evolution of coarse and giant particles and their contribution to optical properties using airborne observations over the Sahara (from the Fennec field campaign) and in the Saharan Air Layer (SAL) over the tropical eastern Atlantic (from the AER-D field campaign). Observations show significantly more abundant coarse and giant dust particles over the Sahara compared to the SAL: effective diameters of up to 20 µm were observed over the Sahara compared to 4 µm in the SAL. Excluding giant particles over the Sahara results in significant underestimation of mass concentration (40 %), as well as underestimates of both shortwave and longwave extinction (18 % and 26 %, respectively, from scattering calculations), while the effects in the SAL are smaller but non-negligible. The larger impact on longwave extinction compared to shortwave implies a bias towards a radiative cooling effect in dust models, which typically exclude giant particles and underestimate coarse-mode concentrations. A compilation of the new and published effective diameters against dust age since uplift time suggests that two regimes of dust transport exist. During the initial 1.5 d, both coarse and giant particles are rapidly deposited. During the subsequent 1.5 to 10 d, PSD barely changes with transport, and the coarse mode is retained to a much greater degree than expected from estimates of gravitational sedimentation alone. The reasons for this are unclear and warrant further investigation in order to improve dust transport schemes and the associated radiative effects of coarse and giant particles in models.

Experimental Verification of the Particle Blocking Feature of Nasal Hair

Although it is well known that nasal hair keeps particles from entering our body, its quantitative evaluation has not been done. In this study, the particle blocking efficiency by nasal hair was studied both experimentally and numerically. The results of laboratory experiments performed with the successfully reconstructed artificial nose indicate that nasal breathing is effective in blocking particle (especially the giant particle lager than 5 µm), especially during the exercise respiration mode. At the exercise respiration pattern, two kinds of coarse particles (i.e., particles of 2-5 µm and >5µm) showed a continuous decrease in particle blocking efficiency (Epb (%)) with increasing breathing duration. All curves drown by the theoretically calculated particle cut-off efficiency of nasal hairs (Einteg.) with three different thicknesses (i.e., 50, 75, and 100 µm) show a minimum (nearly zero) for the particle ranged from 0.004 to 0.4 µm. In the Einteg. curves, the thinner nasal hair can block particles more efficiently through a whole particle size range.

New Isolates of Pandoraviruses: Contribution to the Study of Replication Cycle Steps.

Giant viruses are complex members of the virosphere, exhibiting outstanding structural and genomic features. Among these viruses, the pandoraviruses are some of the most intriguing members, exhibiting giant particles and genomes presenting at up to 2.5 Mb, with many genes having no known function. In this work, we analyzed, by virological and microscopic methods, the replication cycle steps of three new pandoravirus isolates from samples collected in different regions of Brazil. Our data indicate that all analyzed pandoravirus isolates can deeply modify the Acanthamoeba cytoplasmic environment, recruiting mitochondria and membranes into and around the electron-lucent viral factories. We also observed that the viral factories start forming before the complete degradation of the cellular nucleus. Various patterns of pandoravirus particle morphogenesis were observed, and the assembly of the particles seemed to be started either by the apex or by the opposite side. On the basis of the counting of viral particles during the infection time course, we observed that pandoravirus particles could undergo exocytosis after their morphogenesis in a process that involved intense recruitment of membranes that wrapped the just-formed particles. The treatment of infected cells with brefeldin affected particle exocytosis in two of the three analyzed strains, indicating biological variability among isolates. Despite such particle exocytosis, the lysis of host cells also contributed to viral release. This work reinforces knowledge of and reveals important steps in the replication cycle of pandoraviruses.IMPORTANCE The emerging Pandoraviridae family is composed of some of the most complex viruses known to date. Only a few pandoravirus isolates have been described until now, and many aspects of their life cycle remain to be elucidated. A comprehensive description of the replication cycle is pivotal to a better understanding of the biology of the virus. For this report, we describe new pandoraviruses and used different methods to better characterize the steps of the replication cycle of this new group of viruses. Our results provide new information about the diversity and biology of these giant viruses.

Unexpected vertical structure of the Saharan Air Layer and giant dust particles during AER-D

Abstract. The Saharan Air Layer (SAL) in the summertime eastern Atlantic is typically well mixed and 3–4 km deep, overlying the marine boundary layer (MBL). In this paper, we show experimental evidence that at times a very different structure can be observed. During the AERosol properties – Dust (AER-D) airborne campaign in August 2015, the typical structure described above was observed most of the time, and was associated with a moderate dust content yielding an aerosol optical depth (AOD) of 0.3–0.4 at 355 nm. In an intense event, however, an unprecedented vertical structure was observed close to the eastern boundary of the basin, displaying an uneven vertical distribution and a very large AOD (1.5–2), with most of the dust in a much lower level than usual (0.3–2 km). Estimated dust concentrations and column loadings for all flights during the campaign spanned 300–5500 and 0.8–7.5 g m−2, respectively. The shortwave direct radiative impact of the intense dust event has been evaluated to be as large as -260±30 and -120±15 W m−2 at the surface and top of atmosphere (TOA), respectively. We also report the correlation of this event with anomalous lightning activity in the Canary Islands. In all cases, our measurements detected a broad distribution of aerosol sizes, ranging from ∼0.1 to ∼80 µm (diameter), thus highlighting the presence of giant particles. Giant dust particles were also found in the MBL. We note that most aerosol models may miss the giant particles due to the fact that they use size bins up to 10–25 µm. The unusual vertical structure and the giant particles may have implications for dust transport over the Atlantic during intense events and may affect the estimate of dust deposited to the ocean. We believe that future campaigns could focus more on events with high aerosol load and that instrumentation capable of detecting giant particles will be key to dust observations in this part of the world.

Coarse-mode mineral dust size distributions, composition and optical properties from AER-D aircraft measurements over the tropical eastern Atlantic

Abstract. Mineral dust is an important component of the climate system, affecting the radiation balance, cloud properties, biogeochemical cycles, regional circulation and precipitation, as well as having negative effects on aviation, solar energy generation and human health. Dust size and composition has an impact on all these processes. However, changes in dust size distribution and composition during transport, particularly for coarse particles, are poorly understood and poorly represented in climate models. Here we present new in situ airborne observations of dust in the Saharan Air Layer (SAL) and the marine boundary layer (MBL) at the beginning of its transatlantic transport pathway, from the AERosol Properties – Dust (AER-D) fieldwork in August 2015, within the peak season of North African dust export. This study focuses on coarse-mode dust properties, including size distribution, mass loading, shape, composition, refractive indices and optical properties. Size distributions from 0.1 to 100 µm diameter (d) are presented, fully incorporating the coarse and giant modes of dust. Within the MBL, mean effective diameter (deff) and volume median diameter (VMD) were 4.6 and 6.0 µm respectively, giant particles with a mode at 20–30 µm were observed, and composition was dominated by quartz and alumino-silicates at d > 1 µm. Within the SAL, particles larger than 20 µm diameter were always present up to 5 km altitude, in concentrations over 10−5 cm−3, constituting up to 40 % of total dust mass. Mean deff and VMD were 4.0 and 5.5 µm respectively. Larger particles were detected in the SAL than can be explained by sedimentation theory alone. Coarse-mode composition was dominated by quartz and alumino-silicates; the accumulation mode showed a strong contribution from sulfate-rich and sea salt particles. In the SAL, measured single scattering albedos (SSAs) at 550 nm representing d < 2.5 µm were 0.93 to 0.98 (mean 0.97). Optical properties calculated for the full size distribution (0.1 < d < 100 µm) resulted in lower SSAs of 0.91–0.98 (mean 0.95) and mass extinction coefficients of 0.27–0.35 m2 g−1 (mean 0.32 m2 g−1). Variability in SSA was mainly controlled by variability in dust composition (principally iron) rather than by variations in the size distribution, in contrast with previous observations over the Sahara where size is the dominant influence. It is important that models are able to capture the variability and evolution of both dust composition and size distribution with transport in order to accurately represent the impacts of dust on climate. These results provide a new SAL dust dataset, fully representing coarse and giant particles, to aid model validation and development.

Seeds mediated synthesis of giant gold particles on the glass surface

Herein, we present the protocols of synthesis of two types of gold particles which are in the great interest for the purpose of molecular electronics. The first type is the flat prisms with a triangular/hexagonal shape and a lateral size up to ~ 80 µm. They were synthesized directly on a glass surface pretreated with (3-aminopropyl)-triethoxysilane molecules. The second type of particles was synthesized with using gold seeds with diameter of 18 nm. These seeds were deposited on a glass surface coated with APTES. The resulted three-dimensional structures with a form close to spherical increase in size up to 0.5–0.08 µm. Moreover, these particles grew up separately and did not merge during 48 h of synthesis.

The number of genes encoding repeat domain-containing proteins positively correlates with genome size in amoebal giant viruses.

Curiously, in viruses, the virion volume appears to be predominantly driven by genome length rather than the number of proteins it encodes or geometric constraints. With their large genome and giant particle size, amoebal viruses (AVs) are ideally suited to study the relationship between genome and virion size and explore the role of genome plasticity in their evolutionary success. Different genomic regions of AVs exhibit distinct genealogies. Although the vertically transferred core genes and their functions are universally conserved across the nucleocytoplasmic large DNA virus (NCLDV) families and are essential for their replication, the horizontally acquired genes are variable across families and are lineage-specific. When compared with other giant virus families, we observed a near–linear increase in the number of genes encoding repeat domain-containing proteins (RDCPs) with the increase in the genome size of AVs. From what is known about the functions of RDCPs in bacteria and eukaryotes and their prevalence in the AV genomes, we envisage important roles for RDCPs in the life cycle of AVs, their genome expansion, and plasticity. This observation also supports the evolution of AVs from a smaller viral ancestor by the acquisition of diverse gene families from the environment including RDCPs that might have helped in host adaption.