Characterization of aerosol particles during a high pollution episode over Mexico City

Abstract More than 7 thousand wildfires were recorded over Mexico in 2019, affecting almost 640 thousand hectares. Most of these fires occurred during the warm-dry season generating dense smoke plumes, impacting urban areas in the central part of the Mexican plateau. From May 10 to 17, 2019, biomass burning (BB) plumes affected Mexico City (MC) and diffused across the basin, drastically reducing visibility. Due to the severity of this high atmospheric pollution (HAP) episode, the local government declared an environmental contingency, warning the population. Fine particle (PM2.5) concentrations were ~ 2 times higher than the nation's air quality standards. Likewise, aerosol optical measurements indicated that visibility was mainly affected by fine aerosol particles. Electron microscopy analysis of aerosol samples obtained during the HAP days shows a high incidence of strong absorbent soot and tarballs (TB). These types of particles were simultaneously observed in MC and at the high-altitude Altzomoni Atmospheric Observatory (~ 4010 m.a.g.l.). Elemental analysis of the particles shows that the composition is dominated by sulfur and potassium, evidencing a strong influence of the BB emissions, but also suggests the presence of urban pollution from MC at the remote Altzomoni site.

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Characterization of aerosol particles during a high pollution episode over Mexico City

Scientific Reports ◽

10.1038/s41598-021-01873-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Giovanni Carabali ◽

José Villanueva-Macias ◽

Luis A. Ladino ◽

Harry Álvarez-Ospina ◽

Graciela B. Raga ◽

...

Keyword(s):

Mexico City ◽

Urban Areas ◽

Particle Concentration ◽

Aerosol Particles ◽

Quality Standards ◽

X Ray ◽

Smoke Plumes ◽

High Incidence ◽

High Pollution

AbstractMore than 7 thousand wildfires were recorded over Mexico in 2019, affecting almost 640 thousand hectares. Most of these fires occurred during the spring season generating dense smoke plumes, impacting urban areas in the central part of the Mexican plateau. From May 10 to 17, 2019, biomass burning (BB) plumes affected Mexico City (MC) and diffused across the basin, producing PM2.5 levels ~ 2 times higher than the nation's air quality standards. Average PM2.5 concentrations increased sharply from 29.4 ± 7.2 µg m−3 to 65.1 ± 13.6 µg m−3 when the dense smoke plumes were detected. The higher particle concentration impacted the aerosol optical depth (AOD) as values ~ 3 times greater than the annual mean (0.32 ± 0.12) were measured, which resulted in a 17% loss of global horizontal irradiation (GHI). Under these severe pollution conditions, the visibility (Va) was reduced by ~ 80%. The high incidence of strong absorbent particles, such as soot and tarballs was revealed through electron microscopy and X-ray fluorescence (XRF) analysis. These techniques show chemical similarities between MC aerosols and those from the high-altitude (~ 4010 m. a. g. l.) Altzomoni Atmospheric Observatory, evidencing a strong influence of the BB emissions, suggesting a regional transport of these pollutants.

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Material analysis techniques using the ion mill

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167639 ◽

1996 ◽

Vol 54 ◽

pp. 1034-1035

Author(s):

J. P. Benedict ◽

R. M. Anderson ◽

S. J. Klepeis

Keyword(s):

Polished Surface ◽

Surface Material ◽

Analysis Techniques ◽

Material Analysis ◽

Optical Inspection ◽

Electron Microscopy Analysis ◽

Microscopy Analysis ◽

Argon Ions ◽

The Impact ◽

Scanning Electron

Ion mills equipped with flood guns can perform two important functions in material analysis; they can either remove material or deposit material. The ion mill holder shown in Fig. 1 is used to remove material from the polished surface of a sample for further optical inspection or SEM ( Scanning Electron Microscopy ) analysis. The sample is attached to a pohshing stud type SEM mount and placed in the ion mill holder with the polished surface of the sample pointing straight up, as shown in Fig 2. As the holder is rotating in the ion mill, Argon ions from the flood gun are directed down at the top of the sample. The impact of Argon ions against the surface of the sample causes some of the surface material to leave the sample at a material dependent, nonuniform rate. As a result, the polished surface will begin to develop topography during milling as fast sputtering materials leave behind depressions in the polished surface.

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Transmission electron microscopy analysis of planar faults on (001) planes in MoSi2single crystals

Philosophical Magazine A ◽

10.1080/01418610208240063 ◽

2002 ◽

Vol 82 (14) ◽

pp. 2737-2754 ◽

Cited By ~ 2

Author(s):

Susanne Guder ◽

Martin Bartsch ◽

Ulrich Messerschmidt

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Transmission Electron Microscopy Analysis ◽

Transmission Electron ◽

Electron Microscopy Analysis ◽

Microscopy Analysis

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MEMS Based Gravimetric Sensor for the Detection of Ultra-Fine Aerosol Particles

2020 IEEE Sensors ◽

10.1109/sensors47125.2020.9278870 ◽

2020 ◽

Author(s):

Malar Chellasivalingam ◽

Laxmeesha Somappa ◽

Adam M. Boies ◽

Maryam Shojaei Baghini ◽

Ashwin A. Seshia

Keyword(s):

Aerosol Particles ◽

Fine Aerosol

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Effects of Various Antioxidant Pretreatment Modalities on Adhesion to Sound and Caries-Affected Dentin: An In Vitro Study

Journal of Advanced Oral Research ◽

10.1177/2320206821997985 ◽

2021 ◽

pp. 232020682199798

Author(s):

Beyza Unalan Degirmenci ◽

Alperen Degirmenci ◽

Emine Kara

Keyword(s):

Bond Strength ◽

In Vitro Study ◽

Natural Antioxidants ◽

Microtensile Bond Strength ◽

Mandibular Molar ◽

Electron Microscopy Analysis ◽

Molar Teeth ◽

Microscopy Analysis ◽

Two Parameters

Aim: Natural antioxidants were offered as the answer of dentin adhesion issue. The aim of this study is to investigate the effects of proanthocyanidin and lycopene as pretreatment agents on the sound and caries-affected dentin surface on microtensile bond strength and microleakage. Materials and Methods: This study was designed as in vitro because of that 84 mandibular molar teeth were collected. Forty-two of the included teeth were carious teeth, while the other 42 were without caries. Sixty of them were used for microleakage and 24 for microtensile bond strength testing and scanning electron microscopy analysis. The samples were divided into six subgroups randomly according to dentin pretreatments: 5% proanthocyanidin, 5% lycopene, and no antioxidant application. After the restorative procedures, samples were attached to the microtensile tester. Samples were subjected to tensile stress in the load cell until they broke at a speed of 0.5 mm per min. Microtensile bond strength (µTBS) and microleakage test data were analyzed with two-way analysis of variance, Bonferroni correction, and Tamhane’s T2 tests. Results: Two-way variance analysis showed that dentin pretreatment applications, dentin substrate, and the interaction between these two parameters had statistically significant effects on µTBS values ( P < .001). There was no difference between dentin pretreatment applications in terms of microleakage scores ( P > .05). Conclusion: The application of dentin pretreatment with proanthocyanidin is a successful procedure that increases the bond strength in both dentin substrate, while pretreatment with lycopene in caries-affected dentin reduces it.

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Antiparasitic Properties of Cardiovascular Agents against Human Intravascular Parasite Schistosoma mansoni

Pharmaceuticals ◽

10.3390/ph14070686 ◽

2021 ◽

Vol 14 (7) ◽

pp. 686

Author(s):

Raquel Porto ◽

Ana C. Mengarda ◽

Rayssa A. Cajas ◽

Maria C. Salvadori ◽

Fernanda S. Teixeira ◽

...

Keyword(s):

Schistosoma Mansoni ◽

Screening Strategy ◽

Early Infection ◽

Global Public Health ◽

Parasitic Worm ◽

Electron Microscopy Analysis ◽

Health Significance ◽

Microscopy Analysis

The intravascular parasitic worm Schistosoma mansoni is a causative agent of schistosomiasis, a disease of great global public health significance. Praziquantel is the only drug available to treat schistosomiasis and there is an urgent demand for new anthelmintic agents. Adopting a phenotypic drug screening strategy, here, we evaluated the antiparasitic properties of 46 commercially available cardiovascular drugs against S. mansoni. From these screenings, we found that amiodarone, telmisartan, propafenone, methyldopa, and doxazosin affected the viability of schistosomes in vitro, with effective concentrations of 50% (EC50) and 90% (EC90) values ranging from 8 to 50 µM. These results were further supported by scanning electron microscopy analysis. Subsequently, the most effective drug (amiodarone) was further tested in a murine model of schistosomiasis for both early and chronic S. mansoni infections using a single oral dose of 400 mg/kg or 100 mg/kg daily for five consecutive days. Amiodarone had a low efficacy in chronic infection, with the worm and egg burden reduction ranging from 10 to 30%. In contrast, amiodarone caused a significant reduction in worm and egg burden in early infection (>50%). Comparatively, treatment with amiodarone is more effective in early infection than praziquantel, demonstrating the potential role of this cardiovascular drug as an antischistosomal agent.

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Impact Resistance of Epoxy Composites Reinforced with Amazon Guaruman Fiber: A Brief Report

Polymers ◽

10.3390/polym13142264 ◽

2021 ◽

Vol 13 (14) ◽

pp. 2264

Author(s):

Raphael H. M. Reis ◽

Fabio C. Garcia Filho ◽

Larissa F. Nunes ◽

Veronica S. Candido ◽

Alisson C. R. Silva ◽

...

Keyword(s):

Fiber Composite ◽

Impact Resistance ◽

Fiber Composites ◽

Epoxy Composites ◽

Impact Performance ◽

Electron Microscopy Analysis ◽

Ballistic Properties ◽

Microscopy Analysis ◽

Izod Impact ◽

The Impact

Fibers extracted from Amazonian plants that have traditionally been used by local communities to produce simple items such as ropes, nets, and rugs, are now recognized as promising composite reinforcements. This is the case for guaruman (Ischinosiphon körn) fiber, which was recently found to present potential mechanical and ballistic properties as 30 vol% reinforcement of epoxy composites. To complement these properties, Izod impact tests are now communicated in this brief report for similar composites with up to 30 vol% of guaruman fibers. A substantial increase in impact resistance, with over than 20 times the absorbed energy for the 30 vol% guaruman fiber composite, was obtained in comparison to neat epoxy. These results were statistically validated by Weibull analysis, ANOVA, and Tukey’s test. Scanning electron microscopy analysis disclosed the mechanisms responsible for the impact performance of the guaruman fiber composites.

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Tunnel performance during the Puebla-Mexico 19 September 2017 earthquake

Earthquake Spectra ◽

10.1177/8755293020976140 ◽

2020 ◽

Vol 36 (2_suppl) ◽

pp. 288-313

Author(s):

Juan M Mayoral ◽

Gilberto Mosqueda ◽

Daniel De La Rosa ◽

Mauricio Alcaraz

Keyword(s):

Mexico City ◽

Seismic Performance ◽

Urban Areas ◽

Numerical Study ◽

Three Dimensional ◽

Frequency Content ◽

Seismic Performance Evaluation ◽

Ground Deformations ◽

Under Construction ◽

Observed Damage

Seismic performance of tunnels during earthquakes in densely populated areas requires assessing complex interactions with existing infrastructure such as bridges, urban overpasses, and metro stations, including low- to medium-rise buildings. This article presents the numerical study of an instrumented tunnel, currently under construction on stiff soils, located in the western part of Mexico City, during the Puebla-Mexico 19 September 2017 earthquake. Three-dimensional finite difference models were developed using the software FLAC3D. Initially, the static response of the tunnel was evaluated accounting for the excavation technique. Then, the seismic performance evaluation of the tunnel was carried out, computing ground deformations and factors of safety, considering soil nonlinearities. Good agreement was observed between predicted and observed damage during post-event site observations. Once the soundness of the numerical model was established, a numerical study was undertaken to investigate the effect of frequency content in tunnel-induced ground motion incoherence for tunnels built in cemented stiff soils. A series of strong ground motions recorded during normal and subduction events were used in the simulations, considering a return period of 250 years, as recommended in the Mexico City building code. From the results, it was concluded that the tunnel presence leads to important frequency content modification in the tunnel surroundings which can affect low- to mid-rise stiff structures located nearby. This important finding must be taken into account when assessing the seismic risk in highly populated urban areas, such as Mexico City.

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