On airborne tire wear particles along roads with different traffic characteristics using passive sampling and optical microscopy, single particle SEM/EDX, and µ-ATR-FTIR analyses

Tire wear particles (TWPs) are a major category of microplastic pollution produced by friction between tires and road surfaces. This non-exhaust particulate matter (PM) is transported through the air and with runoff leading to environmental pollution and health concerns. Here, we collected airborne PM along paved roads with different traffic volumes and speeds using Sigma-2 passive samplers. Particles entering the samplers deposit onto substrates for analysis, or, as we modified it, directly into small (60 ml) separatory funnels, which is particularly useful with high particle loads, where a density separation aids in isolating the microplastics. We quantified putative TWPs (∼10–80 µm) deposited on the substrates (primarily adhesive tape on glass slides) and in the funnels using stereomicroscopy. Putative TWP deposition rates (particles/cm2/day ± SD) at 5 m from the road were highest near a busy highway (324 ± 129), followed by a boulevard with moderate traffic (184 ± 93), and a slow traffic avenue (29 ± 7). We observed that deposition rates increased within proximity to the highway: 99 ± 54, 180 ± 88, and 340 ± 145 at 30, 15, and 5 m, respectively. We show that TWP abundances (i.e., deposition and mass concentration) increase with vehicle braking (driving behavior). We observed no differences (p \u3e 0.05) between the separatory funnel and adhesive tape collection methods. In addition, we were able to obtain FTIR spectra of TWPs (\u3e10 µm) using µ-ATR-FTIR. Both deserve further scrutiny as novel sampling and analytical approaches. In a separate sampling campaign, we differentiated 1438 particles (∼1–80 µm) deposited on boron substrates into TWP, metal, mineral, and biogenic/organic classes with single particle SEM/EDX analysis based on morpho-textural-chemical classification and machine learning. The results revealed similar concentration trends with traffic (high \u3e moderate \u3e low), with the distribution of particle sources alike for the highway and the moderate road: TWPs (∼38–39%) \u3e biogenic (∼34–35%) \u3e minerals (∼23–26%), and metallic particles (∼2–3%). The low traffic road yielded a much different distribution: biogenic (65%) \u3e minerals (27%) \u3e TWPs (7%) \u3e metallic particles (1%). Overall, this work provides much-needed empirical data on airborne TWPs along different types of roads

Differentiating and quantifying carbonaceous (tire, bitumen, and road marking wear) and non-carbonaceous (metals, minerals, and glass beads) non-exhaust particles in road dust samples from a traffic environment

Tires, bitumen, and road markings are important sources of traffic-derived carbonaceous wear particles and microplastic (MP) pollution. In this study, we further developed a machine-learning algorithm coupled to an automated scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) analytical approach to classify and quantify the relative number of the following subclasses contained in environmental road dust: tire wear particles (TWP), bitumen wear particles (BiWP), road markings, reflecting glass beads, metallics, minerals, and biogenic/organics. The method is non-destructive, rapid, repeatable, and enables information about the size, shape, and elemental composition of particles 2–125 μm. The results showed that the method enabled differentiation\ua0between TWP and BiWP for particles > 20 μm with satisfying results. Furthermore, the relative number concentration of the subclasses was similar in both analyzed size fractions (2–20 μm and 20–125 μm), with minerals as the most dominant subclass (2–20 μm x̄ = 78%, 20–125 μm x̄ = 74%) followed by tire and bitumen wear particles, TBiWP, (2–20 μm x̄ = 19%, 20–125 μm x̄ = 22%). Road marking wear, glass beads, and metal wear contributed to x̄ = 1%, x̄ = 0.1%, and x̄ = 1% in the 2–20-μm fraction and to x̄ = 0.5%,x̄ = 0.2%, and x̄ = 0.4% in the 20–125-μm fraction. The present results show that road dust appreciably consists of TWP and BiWP within both the coarse and the fine size fraction. The study delivers quantitative evidence of the importance of tires, bitumen, road marking, and glass beads besides minerals and metals to wear particlesand MP pollution in traffic environments based on environmental (real-world) sample

Nejapa Tephra: The youngest (c. 1kaBP) highly explosive hydroclastic eruption in western Managua (Nicaragua)

Nejapa Maar (2.5 × 1.4 km, c. 120 m deep), the largest maar along the 15-km-long Holocene Nejapa–Miraflores Lineament (NML), is the source vent of the youngest relatively widespread basaltic tholeiitic tephra blanket (Nejapa Tephra: NT) in western central Nicaragua, as shown by isopachs and isopleths (Rausch and Schmincke, 2008). The NT covers an area of > 10 km2 in W/NW Managua. The minimum total magma volume erupted is estimated as 0.09 km3. Juvenile, dominantly slightly vesicular (20–40 vol.%) basically tachylitic cauliflower-shaped lapilli with an average density of 2.1 g/cm3, make up > 90 vol.% of the deposit, while lithoclasts comprise < 10 vol.% except proximally. This, the paucity of fine-grained tuffs and the dominant plane-parallel bedding all suggest fragmentation by shallow interaction of a rising magma starting to vesiculate and fragment pyroclastically with external water. The complex particles so generated erupted in moderately high eruption columns (at least 7–10 km) and were dominantly deposited as dry to damp, warm to cool fallout. Minor surge transport is inferred from fine-grained, locally cross-bedded tephra beds chiefly north of Nejapa and just west of Asososca Maars. Synvolcanic faulting along the NML is inferred. Faults in the study area indicate that activation of the N–S-trending Nejapa–Miraflores Fault (NMF), representing the western flank of Managua Graben, preceded deposition of NT and underlying Masaya Tuff (c.1.8 ka BP), Chiltepe Pumice (c. 1.9 ka BP) and Masaya Triple Layer (2.1 ka BP). The NT deposit is underlain regionally by a paleosol and topped by a soil. The basal paleosol contains pottery sherds made by the Usulután negative technique during the Late Formative period (700 BCE–300 CE) (2.7–1.7 ka BP). The soil overlying NT contains pottery related to the Ometepe technique dated as between 1350 and 1550 CE (650–450 a BP). These, and the radiocarbon dates of the pottery-bearing paleosols (1245 ± 125 and 535 ± 110 a BP) obtained by Pardo et al. (2008) indicate that Nejapa Maar erupted between c. 1.2 and 0.6 ka BP. Future eruptions in this area of similar magnitude, eruptive and transport mechanisms would represent a major hazard and risk to the densely populated western suburbs of Managua, a city expanding rapidly westward. Assuming a similar eruption scenario, poor-quality roofs, common in Nicaragua, would be prone to collapse up to 12 km peripheral to Nejapa Maar or another close-by eruptive site, and buildings at a distance of up to 500 m are likely to be severely affected. In view of the past frequency of eruptions along the NML, further eruptions are likely to occur in the near future

The Malpaisillo Formation: A sequence of explosive eruptions in the mid to late Pleistocene (Nicaragua, Central America)

The subduction-related volcanic front in Nicaragua consists of the Tertiary “Coyol” member in the eastern highlands and the Quaternary to recent volcanic arc within the Nicaraguan depression. Although the Holocene to recent explosive volcanism has been studied extensively no detailed work has been done on the products of explosive volcanism from Quaternary volcanic complexes comprising also the Malpaisillo and Monte Galán Calderas, the focus of this study. The 11 km-wide Malpaisillo Caldera and ~3.5 km-wide Monte Galán Caldera, located ~50 km northwest of Managua, are surrounded by tens of meters of rhyolitic tephras. These pyroclastic flow and fall deposits extend proximally at least 11 km to the southeast and 23 km to the southwest, with observed depositional thicknesses of >16 m for a single ignimbrite unit (or >25 m for the entire section). Distal deposits are found as far as 350 km offshore in the Pacific. At least twelve highly explosive large-volume eruptive phases with corresponding tephra deposits (LPT = La Paz Centro Tephra, PPT = Punta de Plancha Tephra, LCbT = Lower Chibola Tephra, GT = Guacucal Tephra, UCbT = Upper Chibola Tephra, FeT = La Fuente Tephra, ST = Sabanettas Tephra, MgT = Miralago Tephra, ToT = Tolapa Tephra, LMT, MMT, UMT = Lower, Middle, and Upper Maderas Negras Tephras) are distinguished based on geochemical correlations and similar depositional characteristics. Radiometric 40Ar/39Ar ages indicate that most activity related to the large Malpaisillo Caldera occurred between ~570 and ~420 ka. The large Pleistocene Malpaisillo and Monte Galán Calderas are characterized by a long- lived history and, if evolved, a distinctly alkaline (K2O = 2.3–3.8 wt%; Na2O = 4.0– 4.9 wt%) geochemical signature compared to the other Nicaraguan tephra deposits. As a result, the previously defined Malpaisillo Formation has been considerably extended and revised. Our findings contribute to fill a considerable gap in the long- term eruptive history of Nicaraguan volcanoes, with prominent implications for volcanic hazard evaluation for Nicaragua

A model based two-stage classifier for airborne particles analyzed with Computer Controlled Scanning Electron Microscopy

Computer controlled scanning electron microscopy (CCSEM) is a widely-used method for single airborne particle analysis. It produces extensive chemical and morphological data sets, whose processing and interpretation can be very time consuming. We propose an automated two-stage particle classification procedure based on elemental compositions of individual particles. A rule-based classifier is applied in the first stage to form the main classes consisting of particles containing the same elements. Only elements with concentrations above a threshold of 5 wt% are considered. In the second stage, data of each main class are isometrically log-ratio transformed and then clustered into subclasses, using a robust, model-based method. Single particles which are too far away from any more densely populated region are excluded during training, preventing these particles from distorting the definition of the sufficiently populated subclasses. The classifier was trained with over 55,000 single particles from 83 samples of manifold environments, resulting in 227 main classes and 465 subclasses in total. All these classes are checked manually by inspecting the ternary plot matrix of each main class. Regardless of the size of training data, some particles might belong to still undefined classes. Therefore, a classifier was chosen which can declare particles as unknown when they are too far away from all classes defined during training

Walking through volcanic mud : the 2,100 year-old Acahualina footprints (Nicaragua) II: the Acahualina people, environmental conditions and motivation

We analyzed bare human footprints in Holocene tuff preserved in two pits in the Acahualinca barrio in the northern outskirts of Managua (Nicaragua). Lithology, volcanology, and age of the deposits are discussed in a companion paper (Schmincke et al. Bull Volcanol doi: 10.1007/s00445-008-0235-9, 2008). The footprint layer occurs within a series of rapidly accumulated basaltic–andesitic tephra that is regionally correlated to the Masaya Triple Layer Tephra. The people were probably trying to escape from a powerful volcanic eruption at Masaya Caldera 20 km farther south that occurred at 2.1 ka BP. We subdivided the swath of footprints, up to 5.6 m wide, in the northern pit (Pit I) into (1) a central group of footprints made by about six individuals, the total number being difficult to determine because people walked in each other’s footsteps one behind the other and (2) two marginal groups on either side of the central group with more widely spaced tracks. The western band comprises tracks of three adjacent individuals and an isolated single footprint farther out. The eastern marginal area comprises an inner band of deep footprints made by three individuals and, farther out, three clearly separated individuals. We estimate the total number of people as 15–16. In the southern narrow and smaller pit (Pit II), we recognize tracks of ca. 12 individuals, no doubt made by the same group. The group represented in both pits probably comprised male and female adults, teenagers and children based on differences in length of footprints and of strides and depth of footprints made in the soft wet ash. The smallest footprints (probably made by children) occur in the central group, where protection was most effective. The footprint layer is composed of a lower 5–15-cm thick, coarse-grained vesicle tuff capped by a medium to fine-grained tuff up to 3 cm thick. The surface on which the people walked was muddy, and the soft ash was squeezed up on the sides of the foot imprints and between toes. Especially, deep footprints are mainly due to local thickening of the water-rich ash, multiple track use, and differences in weight of individuals. The excellent preservation of the footprints, ubiquitous mudcracks, sharp and well-preserved squeeze-ups along the margins of the tracks and toe imprints, and the absence of raindrop impressions all suggest that the eruption occurred during the dry season. The people walked at a brisk pace, as judged from the tight orientation of the swath and the length of the strides. The directions of a major erosional channel in the overlying deposits that probably debouched into Lake Managua and the band of footprints are strictly parallel, indicating that people walked together in stride along the eastern margin of a channel straight toward the lake shore, possibly a site with huts and/or boats for protection and/or escape

Pushing the volcanic explosivity index to its limit and beyond: constraints from exceptionally weak explosive eruptions at Kīlauea in 2008

Estimating the mass, volume, and dispersal of the deposits of very small and/or extremely weak explosive eruptions is difficult, unless they can be sampled on eruption. During explosive eruptions of Halema'uma'u Crater (Kīlauea, Hawaii) in 2008, we constrained for the first time deposits of bulk volumes as small as 9–300 m³ (1 × 10⁴ to 8 × 10⁵ kg) and can demonstrate that they show simple exponential thinning with distance from the vent. There is no simple fit for such products within classifications such as the Volcanic Explosivity Index (VEI). The VEI is being increasingly used as the measure of magnitude of explosive eruptions, and as an input for both hazard modeling and forecasting of atmospheric dispersal of tephra. The 2008 deposits demonstrate a problem for the use of the VEI, as originally defined, which classifies small, yet ballistic-producing, explosive eruptions at Kīlauea and other basaltic volcanoes as nonexplosive. We suggest a simple change to extend the scale in a fashion inclusive of such very small deposits, and to make the VEI more consistent with other magnitude scales such as the Richter scale for earthquakes. Eruptions of this magnitude constitute a significant risk at Kīlauea and elsewhere because of their high frequency and the growing number of "volcano tourists" visiting basaltic volcanoes

Decrypting silicic magma/plug fragmentation at Azufral crater lake, Northern Andes: insights from fine to extremely fine ash morpho-chemistry

Azufral (SW Colombia) is a dangerous silicic volcano hosting a crater lake, which serves as an excellent example of an incipient plug disruption through phreatomagmatism. We studied the youngest succession of dilute pyroclastic density currents (PDCs) onlapping the north-eastern crater rim. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy was used to carry out an automated single-particle analysis of fine to extremely fine ash. We were able to obtain fast and accurate chemical analysis and imaging of 15,098 particles within the 250–63-μm and the 63–32-μm size ranges. The 2D form and roughness parameters were determined for 4895 juvenile glassy particles and validated by 3D micro-X ray computer tomography. There are two end members of high (group 1) and low (group 2) roughness juvenile glassy particles. Group 1 comprises high-roughness glass particles with solidity values as low as 0.34 in 2D and 0.33 in 3D, and convexity values as low as 0.33 in 2D and 0.26 in 3D. Group 2 comprises low-roughness glass particles with 2D solidity values < 0.79 and 3D solidity values typically < 0.58. In this group, 2D convexity values are < 0.68 and 3D convexity values are < 0.71. Both end members are mostly discriminated by the 2D Concavity Index (0.14 to 0.77 in group 1 vs. 0.05–0.35 in group 2). The remaining group 3 comprises particles of intermediate roughness values. In this study, we show how an incipient plug developed over a short repose time might be subjected to only a few cycles of vesicle nucleation, collapse and densification, retaining the characteristics of juvenile glass. Each glassy juvenile ash type, defined by a particular morphology, roughness and microtexture can be linked to a density “stratified” conduit model. In Azufral, the capping and conduit lining dense regions and the permeable zones of the incipient plug likely cracked. The newly formed cracks could allow hydraulic forcing caused by external water and induce phreatomagmatic interaction. This interaction favoured the fine fragmentation of the plug while enhancing ongoing magmatic processes. Finally, the variations of bulk componentry provided clues on dilute pyroclastic density current transport and physical fractionation processes by secondary fragmentation, elutriation and interaction with the crater rim