Inventing aerosols: Auguste Trillat (1861-1944) and the medical meteorology of influenza

The history of biological warfare: Human experimentation, modern nightmares and lone madmen in the twentieth century

Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises

The secret behind the mask

Most respiratory infectious diseases may be spread by human exhaled droplets and droplet nuclei. The once-in-a-century coronavirus disease 2019 (COVID-19) pandemic has shown that the airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cannot be ignored. Understanding the movement and transmission of human exhaled droplets and droplet nuclei is of great significance for exploring the basic transmission mechanisms of SARS-CoV-2 and for developing effective engineering control strategies for infectious diseases. In this paper, we summarize research results on transmission of human exhaled droplets and droplet nuclei, in combination with real-time studies focused on COVID-19. First, droplets exhaled by normal speech, coughing and sneezing range from 10–50, 73–100, and 80–340 µm in size, respectively, with small-sized droplets outnumbering large ones. Second, particle size has a significant impact on the movement and spread of droplets. Large droplets rapidly settle in the air and travel a short horizontal distance, with a small-scale infection range of the source, which is the premise of droplet transmission. Small droplets completely evaporate into droplet nuclei before settling to the ground and then travel a long distance with the airflow, which is the premise of airborne transmission (aerosol transmission). However, what constitutes “large droplets”, and how far can they move on earth? Answering these two questions is crucial for establishing the theory for the mechanism of droplet transmission. Therefore, we clarify the definition of the “critical size” and “critical distance” to distinguish between droplet transmission and airborne transmission, which vary with the composition and size of droplets, environmental factors (temperature, humidity, air velocity, etc.), and the form of air distribution. Different research results may have different critical size or critical distance. Subsequently, we discuss droplet evaporation and its influencing factors. The evaporation of droplets is significantly decided by the relative humidity (RH) of the ambient air and the initial size of the droplets. Droplet nuclei, contributing significantly to airborne transmission, usually have a particle size of less than 1 µm. Their diameters are about 0.25 to 0.5 times that of the initial droplets. Additionally, the droplets within critical size could completely evaporate into droplet nuclei in a low-RH air environment, or settle within a critical distance to cause droplet transmission in a high-RH environment. As a result, we consider the critical size of droplets to be about 30–110 µm, and the critical distance for droplet transmission and airborne transmission to be about 2.5 m. Finally, we collect some latest research on COVID-19. The size of the droplet nuclei containing SARS-CoV-2 is mainly distributed in two ranges: 0.25–0.5 and 0.5–1 µm. Taking the high momentum turbulence effect of sneezing or coughing into account, the virus can be transmitted up to 7–8 m away. These results are expected to be applied for understanding the opportunistic airborne transmission of COVID-19 and for the disease control and prevention in engineering and public places.

Why airborne transmission hasn't been conclusive in case of COVID-19? An atmospheric science perspective

The new coronavirus disease (COVID-19), as a new infectious disease, has relatively strong ability to spread from person to person. This paper studies several meteorological factors and air quality indicators between Shenzhen and Wenzhou, China, and conducts modelling analysis on whether the transmission of COVID-19 is affected by atmosphere. A comparative assessment is made on the characteristics of meteorological factors and air quality in these two typical cities in China and their impacts on the spread of COVID-19. The article uses meteorological data and air quality data, including 7 variables: daily average temperature, daily average relative humidity, daily average wind speed, nitrogen dioxide (NO2), atmospheric fine particulate matter (PM2.5), carbon monoxide (CO) and ozone (O3), a distributed lag non-linear model (DLNM) is constructed to explore the correlation between atmospheric conditions and non-imported confirmed cases of COVID-19, and the relative risk is introduced to measure the lagging effects of meteorological factors and air pollution on the number of non-imported confirmed cases. Our finding indicates that there is significant differences in the relationship between 7 predictors and the transmission of COVID-19 in Shenzhen and Wenzhou. However, all predictors between the two cities have a non-linear relationship with the number of non-imported confirmed cases. The lower daily average temperature has increased the risk of epidemic transmission in the two cities. As the temperature rises, the risk of epidemic transmission in both cities will significantly decrease. The average daily relative humidity has no significant effects on the epidemic situation in Shenzhen, but the lower relative humidity reduces the risk of epidemic spread in Wenzhou. In contrast, meteorological data have significant impacts on the spread of COVID-19 in Wenzhou. The four predictors (NO2, PM2.5, CO, and O3) have significant effects on the number of nonimported confirmed cases. Among them, PM2.5 has a significant positive correlation with the number of non-imported confirmed cases. Daily average wind speed, NO2 and O3 have different effects on the number of non-imported confirmed cases in different cities.

Guidance on the use of respiratory and facial protection equipment

How do healthcare workers in diagnostic imaging minimise risks but maximise performance during the COVID-19 pandemic?

Air quality and climate change are of the dominant challenges for Islandic ecosystems in Mediterranean region. This work studies the air quality and the impact of meteorological conditions in pollution levels of Chalki Island, a small island that is located in the climatic sensitive region of southeastern Aegean basin. The analysis was conducted during a low touristic activity period that covers the days from 24th of November 2023 to 3rd of March 2024. Hourly recording of PM2.5, O3 and SO2 as well as meteorological factors of temperature (T) and relative humidity (HR) from a mobile air quality monitoring system (Haz-Scanner™ Model HIM-6000) which is located in the center of city in combination with meteorological parameters (precipitation, planetary boundary height, atmospheric pressure, wind speed and direction) available from the last generation of ECMWF reanalysis dataset (ERA5) are used for the analysis. The calculation of Air Quality Index (AQI) for the studied pollutants shows that PM2.5 is the dominant factor that determines the air quality in the city center of Chalki. The majority of days is classified in “good” and “moderate” air quality classes (in terms of AQI). Additionally, the analysis shows that climate conditions significantly affect the concentration of pollutants. In particular, the higher height of planetary boundary layer (PBL) and increased ventilation coefficient (as a measure of the dispersive capability) are related to improved air quality conditions. The temperature and relative humidity conditions lead to improved climate sense for the mean population (in terms of Discomfort Index; DI

Liquid water is a dominant and critical tropospheric constituent. Over polluted land masses low level cumulus clouds interact with boundary layer aerosol. The planetary boundary layer (PBL) is the lowest atmospheric layer and is directly influenced by Earth's surface. Water-aerosol interactions are critical to processes that govern the fate and transport of trace species in the Earth system and their impacts on air quality, radiative forcing, and regional hydrological cycling. In the PBL, air parcels rise adiabatically from the surface, and anthropogenically influenced hygroscopic aerosols take up water and serve as cloud condensation nuclei (CCN) to form clouds. Water-soluble gases partition to liquid water in wet aerosols and cloud droplets and undergo aqueous-phase photochemistry. Most cloud droplets evaporate, and low volatility material formed during aqueous phase chemistry remains in the condensed phase and adds to aerosol mass. The resulting cloud-processed aerosol has different physicochemical properties compared to the original CCN. Organic species that undergo multiphase chemistry in atmospheric liquid water transform gases to highly concentrated, nonideal ionic aqueous solutions and form secondary organic aerosol (SOA). In recent years, SOA formation modulated by atmospheric waters has received considerable interest.Key uncertainties are related to the chemical nature of hygroscopic aerosols that become CCN and their interaction with organic species. Gas-to-droplet or gas-to-aqueous aerosol partitioning of organic compounds is affected by the intrinsic chemical properties of the organic species in addition to the pre-existing condensed phase. Environmentally relevant conditions for atmospheric aerosol are nonideal. Salt identity and concentration, in addition to aerosol phase state, can dramatically affect organic gas miscibility for many compounds, in particular when ionic strength and salt molality are outside the bounds of limiting laws. For example, Henry's law and Debye-Hückel theory are valid only for dilute aqueous systems uncharacteristic of real atmospheric conditions. Chemical theory is incomplete, and at ambient conditions, this chemistry plays a determining role in total aerosol mass and particle size, controlling factors for air quality and climate-relevant aerosol properties.Accurate predictive skill to understand the impacts of societal choices and policies on air quality and climate requires that models contain correct chemical mechanisms and appropriate feedbacks. Globally, SOA is a dominant contributor to the atmospheric organic aerosol burden, and most mass can be traced back to precursor gas-phase volatile organic compounds (VOCs) emitted from the biosphere. However, organic aerosol concentrations in the Amazon Rainforest, the largest emitter of biogenic VOCs, are generally lower than in U.S. national parks. The Interagency Monitoring of Protected Visual Environments (IMPROVE) air quality network, with sites located predominantly in national parks, provides the longest continuous record of organic aerosol measurements in the U.S. Analysis of IMPROVE data provides a useful chemical climatology of changing air resources in response to environmental rules and shifting economic trends. IMPROVE data provides an excellent test bed for case studies to assess model skill to accurately predict changes in organic aerosol concentrations in the context of a changing climate.

Most coronavirus infections are transmitted via respiratory droplets through the mucosa or direct inhalation route and are manifested as respiratory diseases. However, human coronaviruses such as SARS-CoV-2 (the COVID-19 virus) show environmental resistance that makes airborne transmission plausible. According to published evidence related to COVID-19, airborne transmission through droplet nuclei that propagate in air is limited to aerosol generating procedures during clinical care of COVID-19 patients. However, recent experimental studies have indicated that SARS-CoV-2 can remain viable in airborne aerosols potentially for hours. Studies in hospitals in Iran and China have reported undetectable levels of airborne SARS-CoV-2 RNA at distances over 2 m from patients’ beds or in well sanitised spaces. Although fine particles, pollen and dust in ambient air have all been linked to other infectious diseases in the past, their role in the transmission of COVID-19 and other coronaviruses has not been systematically reviewed so far. Theoretically, inhalation of virus-laden airborne particles could transport the virus deeper into alveolar regions, which could increase the risk of infective transmission. In this rapid systematic review, we analyse the evidence on airborne transmission of COVID-19 and other coronaviruses in outdoor and indoor settings. We investigate how aerosols, including droplets, droplet nuclei, smoke particles, dust, pollen and other aeroallergens may act as carriers of coronaviruses in the air and into the human respiratory system causing infection. We analyse peer-reviewed studies (published or accepted) reporting on airborne transmission of any human coronavirus, including SARS-CoV-2. We include experimental, epidemiological, and mathematical modelling studies in any human population. No restrictions are imposed on the health status or age of these populations or setting (outdoor, indoor, residential, occupational). The primary outcomes of the review are confirmed coronavirus infections as well as positive environmental samples. We searched PubMed, MEDLINE, Scopus, Cochrane Library, and relevant government agency databases.

Abstract. High-altitude remote sites are unique places to study aerosol–cloud interactions, since they are located at the altitude where clouds may form. At these remote sites, organic aerosols (OAs) are the main constituents of the overall aerosol population, playing a crucial role in defining aerosol hygroscopicity (κ). To estimate the cloud condensation nuclei (CCN) budget at OA-dominated sites, it is crucial to accurately characterize OA hygroscopicity (κOA) and how its temporal variability affects the CCN activity of the aerosol population, since κOA is not well established due to the complex nature of ambient OA. In this study, we performed CCN closures at a high-altitude remote site during summer to investigate the role of κOA in predicting CCN concentrations under different atmospheric conditions. In addition, we performed an OA source apportionment using positive matrix factorization (PMF). Three OA factors were identified from the PMF analysis: hydrocarbon-like OA (HOA), less-oxidized oxygenated OA (LO-OOA), and more-oxidized oxygenated OA (MO-OOA), with average contributions of 5 %, 36 %, and 59 % of the total OA, respectively. This result highlights the predominance of secondary organic aerosol (SOA) with a high degree of oxidation at this high-altitude site. To understand the impact of each OA factor on the overall OA hygroscopicity, we defined three κOA schemes that assume different hygroscopicity values for each OA factor. Our results show that the different κOA schemes lead to similar CCN closure results between observations and predictions (slope and correlation ranging between 1.08–1.40 and 0.89–0.94, respectively). However, the predictions were not equally accurate across the day. During the night, CCN predictions underestimated observations by 6 %–16 %, while, during morning and midday hours, when the aerosol was influenced by vertical transport of particles and/or new particle formation events, CCN concentrations were overestimated by 0 %–20 %. To further evaluate the role of κOA in CCN predictions, we established a new OA scheme that uses the OA oxidation level (parameterized by the f44 factor) to calculate κOA and predict CCN. This method also shows a large bias, especially during midday hours (up to 40 %), indicating that diurnal information about the oxygenation degree does not improve CCN predictions. Finally, we used a neural network model with four inputs to predict CCN: N80 (number concentration of particles with diameter > 80 nm), OA fraction, f44, and solar global irradiance. This model matched the observations better than the previous approaches, with a bias within ± 10 % and with no daily variation, reproducing the CCN variability throughout the day. Therefore, neural network models seem to be an appropriate tool to estimate CCN concentrations using ancillary parameters accordingly.

Grain is the relationship between the people's livelihood and social stability of the special goods, is the stability of the world's important strategic materials, but also is the human survival and social development of a solid foundation, the world attaches great importance to this. Grain production is closely related to climate factors, especially in the current stage of serious ecological environment destruction. Climate change has become an important factor affecting grain production and security. The scholars speculate that in the next 20–50 years, China's agriculture will be seriously affected by climate factors, and the grain production will be adversely affected. Analysis of meteorological factors affecting grain production, with a view to the development of food policy and the implementation of grain security system control to provide rationalization proposals. Wheat is one of the main grain crops in China, and annual planting area and total yield are second only to rice and maize. Henan is a major grain production province in China, which mainly grow winter wheat. During the whole growth and development of winter wheat, the meteorological factors such as temperature, light and rainfall are important environmental factors that affect the normal growth of winter wheat. Many scholars at home and abroad have done a lot of fruitful work in the field of meteorology and wheat production. Chinese studies on meteorology and grain production can be traced back to the Northern Wei Dynasty. China's outstanding agronomist Jia Sixie, in his book “Qi Min Yao Shu” described in detail the seasons, climates, crops and their mutual relationships. Most of the above research methods are based on the principle of statistics and fuzzy mathematics to study the effect of meteorological factors on the yield of wheat growth period. The grain production system itself is a grey system, which is influenced by many influencing factors. The large sample of data defects, for food production system is no longer applicable, and grey system theory just to make up for the mathematical statistics method defects. The existing literature review focuses on the impact of meteorological factors on the yield of grain during the whole growth period, there is little literature about combining phenology changes to study the influence of meteorological factors on different growth stages of crops, the results are not well explained its various growth stages of the impact mechanism. In order to explore the influence of meteorological factors in different growth stages of crops, this paper firstly chooses winter wheat in Henan province as research object by dividing the winter wheat growth period into nine growth stages according to the phonological map. Then the study selects the yield data and daily average meteorological data of winter wheat in Henan province from 2005 to 2015 and uses the exponential smoothing method to calculate the meteorological yield of winter wheat, and finally establishes the meteorological factors set and the grey relational analysis model to doubly analyze the influence of meteorological factors on winter wheat in different growth stages. The results show that in the case of single analysis, the average relative humidity has the greatest influence on meteorological yield of winter wheat during sowing stage, tillering stage, overwintering stage and grouting stage; the mean wind speed has the greatest influence on meteorological yield of winter wheat during the period of reviving stage, jointing stage and maturing stage; the average daily temperature has the greatest influence on meteorological yield of winter wheat during the seeding stage; the duration of illumination has the greatest influence on meteorological yield of winter wheat during the heading stage. In the case of double quantitative analysis, the meteorological yield of winter wheat was influenced by the average relative temperature and the daily maximum temperature at the seedling stage, the average relative humidity of the tillering stage and the overwintering stage and the mean wind speed of jointing stage. Generally speaking, the results of this study are in agreement with previous studies, And this article more comprehensive and specific study of the whole growth stage of winter wheat different meteorological factors on the impact of meteorological production. Through the study of the influence of meteorological factors on grain yield, it is of great significance to the sustainable development of agriculture in Henan province and to improve the economic strength of Henan province, which is of theoretical significance to the social and economic development of the province and the improvement of grain yield.

Background and AimsCystic fibrosis (CF) is characterised by repeated bacterial respiratory infections and progressive lung disease. While Pseudomonas aeruginosa is the most prevalent organism recovered from the respiratory secretions of people with CF, other species including Staphylococcus aureus, Stenotrophomonas maltophilia, Achromobacter species, Burkholderia cepacia complex species, and Mycobacterium abscessus may also be detected. The majority of these pathogens are found in the natural environment and the identification of genetically diverse bacterial strains infecting people with CF would suggest that this is the most common acquisition source. However, epidemiological studies have demonstrated that some people with CF may harbour genetically indistinguishable (shared) strains of organisms. Common environmental reservoirs have not been identified for many shared strains, suggesting that person-to-person transmission may be a method of acquisition, although the exact mechanisms involved are unclear. The airborne route, involving inhalation of microbe-containing droplet nuclei, has been speculated as a possible transmission pathway.Previous studies have demonstrated that people with CF can generate droplet nuclei containing P. aeruginosa, which can survive for up to 45-minutes and can travel up to 4-metres from their source and therefore potentially capable of airborne transmission. The survival of other common CF pathogens over distance and time is not known. Recent updates to CF infection control guidelines in some countries recommend the use of a surgical face mask for people with CF to minimise risk of transmission and acquisition of such pathogens. The effectiveness of face masks in a CF population has not been studied extensively.To address the knowledge gaps highlighted above, this thesis had two key aims:i) To determine if CF pathogens other than P. aeruginosa can be aerosolised during coughing, and to investigate their survival in the air over distance and time and;ii) To examine the effectiveness of face masks and cough etiquette in reducing the outward dispersal of cough generated aerosols containing P. aeruginosa in people with CF.Methodsi) Cough aerosolisation of cystic fibrosis respiratory pathogens (other than P. aeruginosa) Thirty-three participants with CF were enrolled, according to a recent history of infection with: 1) Gram-negative bacteria (GNB) other than P. aeruginosa; 2) S. aureus and; 3) M. abscessus complex. Using two validated systems for aerosol sampling, the viability and survival of cough aerosols were measured over distance and time.ii) Effectiveness of face masks and cough etiquette to reduce aerosol concentration of Pseudomonas aeruginosa Twenty-five participants with CF and chronic P. aeruginosa infection were enrolled. Six respiratory activities of talking and coughing, with and without face masks were undertaken within an aerosol sampling device. Aerosols were collected at 2-metres and quantitative analysis performed on bacterial colony forming units (CFU) for each intervention. Subjects rated their comfort levels when wearing masks during each cough activity.ResultsPeople with CF and respiratory infections including: S. maltophilia, Achromobacter spp., B. cepacia spp., and S. aureus can aerosolise these organisms during coughing. All species were detected within droplet nuclei at 4-metres from source and up to 45-minutes after generation. A correlation between bacterial aerosol concentration and sputum load was demonstrated for GNB (r=0.50, p=0.035) and S. aureus (r=0.66, p=0.005) (Chapter 2).M. abscessus can be aerosolised during coughing and survive (presumably on inanimate surfaces) for up to 24-hours. Viable aerosols were detected when there was greater burden of respiratory infection (Chapter 3).During uncovered coughing, 19/25 (76%) subjects produced viable P. aeruginosa aerosols at 2- metres, with a positive correlation observed between the P. aeruginosa sputum load and the aerosol bacterial concentration (r=0.55, p=0.01). The surgical mask (p˂0.001), the N95 mask (p˂0.001) and cough etiquette (p˂0.001) were effective at reducing cough aerosols containing P. aeruginosa by 94, 94 and 53%, respectively when compared to uncovered coughing. The surgical mask was rated more comfortable than the N95 mask (p=0.004) (Chapter 4).ConclusionsThis thesis demonstrates that common CF pathogens are aerosolised during coughing and survive for extended periods within droplet nuclei, suggesting that airborne transmission is plausible for the organisms measured. This finding suggests that stringent infection control practices are required for people with CF.Face masks significantly reduce the outward dispersal of cough generated P. aeruginosa aerosols, whereas cough etiquette is less effective. These data support the recent infection control recommendations for people with CF to wear a surgical mask in common areas of healthcare facilities to reduce potential transmission of pathogens.

Purpose of ReviewSeveral studies have found that air pollution and climate change can have an impact on acute coronary syndromes (ACS), the leading cause of death worldwide. We synthesized the latest information about the impact of air pollution and climate change on ACS, the latest data about the pathophysiological mechanisms of meteorological factors and atmospheric pollutants on atherosclerotic disease, and an overall image of air pollution and coronary heart disease in the context of the COVID-19 pandemic.Recent FindingsThe variation of meteorological factors in different seasons increased the risk of ACS. Both the increase and the decrease in apparent temperature were found to be risk factors for ACS admissions. It was also demonstrated that exposure to high concentrations of air pollutants, especially particulate matter, increased cardiovascular morbidity and mortality.SummaryClimate change as well as increased emissions of air pollutants have a major impact on ACS. The industrialization era and the growing population cause a constant increase in air pollution worldwide. Thus, the number of ACS favored by air pollution and the variations in meteorological factors is expected to increase dramatically in the next few years.