The effect of (NH₄)₂SO₄ on the freezing properties of non-mineral dust ice-nucleating substances of atmospheric relevance

A wide range of materials including mineral dust, soil dust, and bioaerosols have been shown to act as ice nuclei in the atmosphere. During atmospheric transport, these materials can become coated with inorganic and organic solutes which may impact their ability to nucleate ice. While a number of studies have investigated the impact of solutes at low concentrations on ice nucleation by mineral dusts, very few studies have examined their impact on non-mineral dust ice nuclei. We studied the effect of dilute (NH4)2SO4 solutions (0.05 M) on immersion freezing of a variety of non-mineral dust ice-nucleating substances (INSs) including bacteria, fungi, sea ice diatom exudates, sea surface microlayer substances, and humic substances using the droplet-freezing technique. We also studied the effect of (NH4)2SO4 solutions (0.05 M) on the immersion freezing of several types of mineral dust particles for comparison purposes. (NH4)2SO4 had no effect on the median freezing temperature (ΔT50) of 9 of the 10 non-mineral dust materials tested. There was a small but statistically significant decrease in ΔT50 (−0.43 ± 0.19 ∘C) for the bacteria Xanthomonas campestris in the presence of (NH4)2SO4 compared to pure water. Conversely, (NH4)2SO4 increased the median freezing temperature of four different mineral dusts (potassium-rich feldspar, Arizona Test Dust, kaolinite, montmorillonite) by 3 to 9 ∘C and increased the ice nucleation active site density per gram of material (nm(T)) by a factor of ∼ 10 to ∼ 30. This significant difference in the response of mineral dust and non-mineral dust ice-nucleating substances when exposed to (NH4)2SO4 suggests that they nucleate ice and/or interact with (NH4)2SO4 via different mechanisms. This difference suggests that the relative importance of mineral dust to non-mineral dust particles for ice nucleation in mixed-phase clouds could potentially increase as these particles become coated with (NH4)2SO4 in the atmosphere. This difference also suggests that the addition of (NH4)2SO4 (0.05 M) to atmospheric samples of unknown composition could potentially be used as an indicator or assay for the presence of mineral dust ice nuclei, although additional studies are still needed as a function of INS concentration to confirm the same trends are observed for different INS concentrations than those used here. A comparison with results in the literature does suggest that our results may be applicable to a range of mineral dust and non-mineral dust INS concentrations.

Mixed-dust Pneumoconiosis in a Dental Technician: A Multidisciplinary Diagnosis

BackgroundExposure to crystalline silica in dental laboratories can occur during procedures that generate suspended mineral dusts, e.g. dispersion of mixing powders, removal of castings from moulds grinding and polishing castings and porcelain, and use of silica sand for blasting. Case presentationWe report a 55-year-old male dental technician who, after about 15 years of work, began to suffer from a dry cough and dyspnoea on exertion. The operations included in his job resulted in the generation of crystalline silica, aluminium, chromium, titanium dust. The worker did not regularly wear personal protective equipment and some of the above operations were not carried out in closed circuit systems.The Chest X-ray showed diffuse micronodulation in the lung interstitium in the upper-middle lobes bilaterally and a modest left basal pleural effusion, simple spirometry showed initial small airway obstruction, High Resolution Computerized Tomography of the chest showed bilateral micronodulation of a miliariform type, with greater profusion in the upper lobes, also present in the visceral pleura, bilaterally. Histological examination showed aggregates of pigment-laden macrophages forming perivascular macules or arranged in a radial pattern around a core of sclerohyalinosis. Scanning Electron Microscopy and Energy Dispersive Spectrometry revealed several mineral particles, whose composition is characterised by the presence of aggregates of crystalline silica and metals. The ambient concentrations of total dust and its respirable fraction were all lower than the relative TLV-TWA - ACGIH, but did not negligible. ConclusionsThe above findings and a multidisciplinary assessment led to the diagnosis of mixed dust pneumoconiosis s/q with 2/2 profusion of occupational origin. This diagnosis in a dental technician was supported by environmental exposure analysis for the first time in the literature.

Work-Related Asthma

Work-related asthma encompasses both new-onset asthma and aggravation of pre-existing asthma from work exposures/conditions. New-onset asthma can be caused by exposure to an irritant or a substance that causes sensitization. Approximately 350 substances have been identified by which exposure at work can lead to sensitization and asthma. When the term occupational asthma is used, it generally does not include work-aggravated asthma. Some authors limit the use of occupational asthma to new-onset asthma from sensitization to a substance at work, while others also include new-onset asthma from exposure to an irritant at work under this category. New-onset asthma from an acute single exposure is called reactive airways dysfunction Syndrome (RADS) (note this is not the same as reactive airways disease). New-onset asthma from repeated chronic exposure to an irritant at work as a cause of asthma has also been described, but it is not as well accepted as an entity as RADS. Aggravation of pre-existing asthma by work can occur from any exposure as well as stress, physical activity, and temperature/humidity. Unlike the work-related lung diseases such as the pneumoconioses, which cause irreversible fibrosis, work-related asthma is potentially completely reversible if diagnosed soon after onset of symptoms and the patient’s exposure to the etiologic agent ceases. Beginning in the early 1900s, asthma from exposure at work to plant material and metals first began to be reported in the medical literature. In the 1970s, Dr. Jack Pepys from England markedly advanced the identification of etiological agents by developing a practical way to perform specific inhalation challenge testing. The field has continued to advance with the recognition of an increased number of etiological agents, an understanding of the pathophysiology, an understanding of the prognosis and factors associated with a better prognosis, and the initiation of work on the interaction with genetic variability. At least in more developed countries, such as in European countries and the United States, which have implemented controls or banned the use of the mineral dusts (i.e., asbestos, silica) that have caused the most common pneumoconioses, work-related asthma has become a more important cause of new-onset work-related lung disease than the more traditional pneumoconioses.

The effect of (NH₄)₂SO₄ on the freezing properties of non-mineral dust ice nucleating substances of atmospheric relevance

A wide range of materials including mineral dust, soil dust, and bioaerosols have been shown to act as ice nuclei in the atmosphere. During atmospheric transport, these materials can become coated with inorganic and organic solutes which may impact their ability to nucleate ice. While a number of studies have investigated the impact of solutes at low concentrations on ice nucleation by mineral dusts, very few studies have examined their impact on non-mineral dust ice nuclei. We studied the effect of dilute (NH4)2SO4 solutions on immersion freezing of a variety of non-mineral dust ice nucleating substances including bacteria, fungi, sea ice diatom exudates, sea surface microlayer, and humic substances using the droplet freezing technique. We also studied the effect of (NH4)2SO4 on immersion freezing of mineral dust particles for comparison purposes. (NH4)2SO4 had no effect on the median freezing temperature of nine of the ten tested non-mineral dust materials. There was a small but statistically significant decrease in the median freezing temperature of the bacteria X. campestris (change in median freezing temperature ∆T_50 = -0.43 ± 0.19 °C) in the presence of (NH4)2SO4 compared to pure water. Conversely, (NH4)2SO4 increased the median freezing temperature of four different mineral dusts (Potassium-rich feldspar, Arizona Test Dust, Kaolinite, Montmorillonite) by 3 °C to 8 °C. This significant difference in the response of mineral dust and non-mineral dust ice nucleating substances when exposed to (NH4)2SO4 suggests that they nucleate ice and/or interact with (NH4)2SO4 via different mechanisms. This difference suggests that the relative importance of mineral dust to non-mineral dust particles for ice nucleation in mixed-phase clouds could increase as these particles become coated with ammonium sulfate in the atmosphere. This difference also suggests that the addition of (NH4)2SO4 to atmospheric samples of unknown composition could be used as an indicator or assay for the presence of mineral dust ice nuclei.

THE FORMATION OF HIGH TEMPERATURE MINERALS FROM AN EVAPORITE-RICH DUST IN GAS TURBINE ENGINE INGESTION TESTS

The ingestion of multi-mineral dusts by gas turbine engines during routine operations is a significant problem for engine manufacturers because of the damage caused to engine components and their protective thermal barrier coatings. A complete understanding of the reactions forming these deposits is limited by a lack of knowledge of compositions of ingested dusts and unknown engine conditions. Past engine tests have used standardised test dusts that do not resemble the composition of the background dust in the operating regions. A new evaporite-rich test dust was developed and used in a full engine ingestion test, designed to simulate operation in regions with evaporite-rich geology, such as Doha or Dubai. Analysis of the engine deposits showed that mineral fractionation was present in the cooler, upstream sections of the engine. In the hotter, downstream sections, deposits contained new, high temperature phases formed by reaction of minerals in the test dust. The mineral assemblages in these deposits are similar to those found from previous analysis of service returns. Segregation of anhydrite from other high temperature phases in a deposit sample taken from a High Pressure Turbine blade suggests a relationship between temperature and sulfur content. This study highlights the potential for manipulating deposit chemistry to mitigate the damage caused in the downstream sections of gas turbine engines. The results of this study also suggest that the concentration of ingested dust in the inlet air may not be a significant contributing factor to deposit chemistry.

Atmospheric oxidation of fluoroalcohols initiated by ·OH radical in the presence of water and mineral dusts: Mechanism, kinetics, and risk assessment

The transport and formation of fluorinated compounds are greatly significant due to their possible environmental risks. In this work, the ·OH-mediated degradation of CF3CF2CF2CH2OH and CF3CHFCF2CH2OH in the existence of...

The Formation of High Temperature Minerals From an Evaporite-Rich Dust in Gas Turbine Engine Ingestion Tests

The ingestion of multi-mineral dusts by gas turbine engines during routine operations is a significant problem for engine manufacturers because of the damage caused to engine components and their protective thermal barrier coatings. A complete understanding of the reactions forming these deposits is limited by a lack of knowledge of compositions of ingested dusts and unknown engine conditions. Test bed engines can be dosed with dusts of known composition under controlled operating conditions, but past engine tests have used standardised test dusts that do not resemble the composition of the background dust in the operating regions. A new evaporiterich test dust was developed and used in a full engine ingestion test, designed to simulate operation in regions with evaporiterich geology, such as Doha or Dubai. Analysis of the engine deposits showed that mineral fractionation was present in the cooler, upstream sections of the engine. In the hotter, downstream sections, deposits contained new, high temperature phases formed by reaction of minerals in the test dust. The mineral assemblages in these deposits are similar to those found from previous analysis of service returns. Segregation of anhydrite from other high temperature phases in a deposit sample taken from a High Pressure Turbine blade suggests a relationship between temperature and sulfur content. This study highlights the potential for manipulating deposit chemistry to mitigate the damage caused in the downstream sections of gas turbine engines. The results of this study also suggest that the concentration of ingested dust in the inlet air may not be a significant contributing factor to deposit chemistry.

Bronchiolitis and Bronchiolar Disorders

Bronchioles are noncartilaginous small airways with internal diameter of 2 mm or less, located from approximately the eighth generation of purely air conducting airways (membranous bronchioles) down to the terminal bronchioles (the smallest airways without alveoli) and respiratory bronchioles (which communicate directly with alveolar ducts and are in the range of 0.5 mm or less in diameter). Bronchiolar injury, inflammation, and fibrosis may occur in myriad disorders including connective tissue diseases, inflammatory bowel diseases, lung transplant allograft rejection, graft versus host disease in allogeneic stem cell recipients, neuroendocrine cell hyperplasia, infections, drug toxicity (e.g., penicillamine, busulfan), inhalation injury (e.g., cigarette smoke, nylon flock, mineral dusts, hard metals, Sauropus androgynous); idiopathic, common variable immunodeficiency disorder, and a host of other disorders or insults. The spectrum of bronchiolar disorders is wide, ranging from asymptomatic to fatal obliterative bronchiolitis. In this review, we discuss the salient clinical, radiographic, and histological features of these diverse bronchiolar disorders, and discuss a management approach.