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We review recent results on the formation and evolution of aqueous organic aerosols via concurrent nucleation/condensation and chemical aging processe…

****!!!!*** {Also see citing documents at agupubs.onlinelibrary.wiley.com/doi/10.1029/RG021i004p00903} "organic films... If present, they will increase the lifetimes of aerosol particles... both by inhibiting water vapor evaporation and by reducing the efficiency with which these atmospheric components are scavenged. The presence of the films will not cause a significant reduction of solar radiation within the aqueous solution. It appears likely, however, that the transport of gaseous molecules into and out of the aqueous solution will be impeded by factors of several hundred or more when organic films are present. Since incorporated gas molecules provide much of the oxidizing potential of atmospheric water droplets, the organic films will play a major role in droplet chemistry by strongly inhibiting solution oxidation"

"Airborne transmission arises through the inhalation of aerosol droplets exhaled by an infected person and is now thought to be the primary transmission route of COVID-19. By assuming that the respiratory droplets are mixed uniformly through an indoor space, we derive a simple safety guideline for mitigating airborne transmission that would impose an upper bound on the product of the number of occupants and their time spent in a room. Our theoretical model quantifies the extent to which transmission risk is reduced in large rooms with high air exchange rates, increased for more vigorous respiratory activities, and dramatically reduced by the use of face masks. Consideration of a number of outbreaks yields self-consistent estimates for the infectiousness of the new coronavirus."

(1996). Nasal Pathology and infrastructure in Patients with Chronic Airway Inflammation (RADS and RUDS) Following an Irritant Exposure. Journal of Toxicology: Clinical Toxicology: Vol. 34, No. 4, pp. 383-396.

Coughs and sneezes feature turbulent, multiphase flows that may contain pathogen-bearing droplets of mucosalivary fluid. As such, they can contribute to the spread of numerous infectious diseases, including influenza and SARS. The range of contamination of the droplets is largely determined by their size. However, major uncertainties on the drop size distributions persist. Here, we report direct observation of the physical mechanisms of droplet formation at the exit of the mouth during sneezing. Specifically, we use high-speed imaging to directly examine the fluid fragmentation at the exit of the mouths of healthy subjects. We reveal for the first time that the breakup of the fluid into droplets continues to occur outside of the respiratory tract during violent exhalations. We show that such breakup involves a complex cascade of events from sheets, to bag bursts, to ligaments, which finally break into droplets. Finally, we reveal that the viscoelasticity of the mucosalivary fluid plays an important role in delaying fragmentation by causing the merger of the droplet precursors that form along stretched filaments; thereby affecting the final drop size distribution farther downstream.

As a place of healing and recovery, hospital air quality is even more important than the air quality at commercial offices and shopping malls. The purpose of a hospital is to return people to good health, and an essential aspect of this process is ensuring that airborne pollutants do not make existing conditions worse.

There are so far no intervention studies investigating biocides in air conditioning systems. -The sick building syndrome (SBS) consists of a group of mucosal, skin, and general symptoms that are temporally related to working in particular buildings. It is the workers who are symptomatic, but the building or its services which are the cause. The common symptoms and a method of assessment are shown in box 2. The average number of work related symptoms per occupant is known as the building symptom index. It can be measured reproducibly by simple questionnaire surveys. The building symptom index shows a wide variation between different buildings (fig 1); “sicker” buildings often have conditions of air temperature, humidity, and lighting levels that fully comply with current standards. Some of the reproducible “facts” shown in studies in different countries are shown in box 1, and factors related to higher (sicker) building symptom indices shown in box 3. Box 4 shows the WHO standards for the management of building ventilation systems. Money spent on the building services is likely to be cost effective in terms of the lost productivity in symptomatic workers. Figure 1 Range of building symptom indices in a group of buildings studied with the same questionnaire with a maximum of 10 symptoms (the actual BSI is dependent on the number of possible positive answers and differs between questionnaires). ### Box 1: Reproducible observations related to sick building syndrome (?facts)

**!!!!*** "Airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing, and social distancing programs." "Aerosols can accumulate, remain infectious in indoor air for hours, and be easily inhaled deep into the lungs. A competition between droplet size, inertia, gravity, and evaporation determines how far emitted droplets and aerosols will travel in air. Larger respiratory droplets will undergo gravitational settling faster than they evaporate, contaminating surfaces and leading to contact transmission. Smaller droplets and aerosols will evaporate faster than they can settle, are buoyant, and thus can be affected by air currents, which can transport them over longer distances. ...Respiratory droplet size has been shown to affect the severity of disease. For example, influenza virus is more commonly contained in aerosols with sizes below 1 µm (submicron), which lead to more severe infection. In the case of (SARS-CoV-2), it is possible that submicron virus-containing aerosols are being transferred deep into the alveolar region of the lungs, where immune responses seem to be temporarily bypassed. SARS-CoV-2 has been shown to replicate three times faster than SARS-CoV-1 and thus can rapidly spread to the pharynx, from which it can be shed before the innate immune response becomes activated and produces symptoms. By the time symptoms occur, the patient has transmitted the virus without knowing.... The US CDC recommendations... are based on studies of respiratory droplets carried out in the 1930s. In outdoor environments, numerous factors will determine the concentrations and distance traveled, and whether respiratory viruses remain infectious in aerosols. Overall, the probability of becoming infected indoors will depend on the total amount of SARS-CoV-2 inhaled. Ultimately, the amount of ventilation, number of people, how long one visits an indoor facility, and activities that affect airflow will all modulate viral transmission pathways and exposure. Universal masking is highly important."

The practice of social distancing and wearing masks has been popular worldwide in combating the contraction of COVID-19. Undeniably, although such practices help control the COVID-19 pandemic to a greater extent, the complete control of virus-laden droplet ...

More and more evidence suggests that the Covid-19 coronavirus can spread via aerosols, which is changing the strategies on how to deal with the virus.

Wearing masks at home -While tiny viral particles might travel through the air, it's unclear whether they could make someone else sick.

Physical filtration efficiencies may not directly translate to effectiveness in mitigating virus transmission. More effectiveness studies with biological measures (e.g. viral load and infection events) as outcomes are needed.

An inactivation of airborne pathogenic Middle East Respiratory Syndrome (MERS-CoV) virus was investigated under controlled laboratory conditions. Two …

Influenza A Virus (IAV) replications start from the deposition of inhaled virus-laden droplets on the epithelial cells in the pulmonary tracts. In ord…

The impact of ambient relative humidity (RH) and airflow patterns on the evaporation and dispersion of infectious droplets exhaled from an infector wa…

(2020). The coronavirus pandemic and aerosols: Does COVID-19 transmit via expiratory particles? Aerosol Science and Technology: Vol. 54, No. 6, pp. 635-638.

Humidifiers are commonly used in the community to relieve symptoms associated with acute respiratory infections in young children; however, clear benefits of these devices have not been documented. The Environmental Protection Agency has not found any adverse health effects related to humidifier use. We report here the case of a young infant with significant accidental inhalational lung injury related to dispersal of mineral dust from an ultrasonic home-use humidifier. The clinical consequences included prolonged hypoxemia, tachypnea, and failure to thrive. Radiography revealed pneumonitis, and pulmonary-function testing showed a nonreversible mild obstructive ventilatory defect. Because of persistent symptoms, evolution of failure to thrive, and nonresponse to inhaled and short courses of systemic glucocorticoids, an aggressive management approach was successfully pursued with high-dose pulse steroid therapy, which could be a potential therapeutic approach for similar patients. In addition, this case raises important questions about the safety of exposing infants and young children to humidifiers and emphasizes the need for further study.

Fate and Transport of Indoor Microbiological Aerosols (FaTIMA) tool based on CONTAM. National Institute of Standards and Technology

Particle pollution in ai is the term for a mixture of solid particles and liquid droplets found in the air. These include "inhalable coarse particles," with diameters between 2.5 micrometers and 10 micrometers, and "fine particles," 2.5 micrometers and smaller.

In conclusion, the frequency of indoor and outdoor allergens in state of Qatar, based on skin prick test study showed the dominance of house dust mites, pollen, grasses which are more or less same to other countries with similar and even with different climate. Reduced exposure to these agents will …

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1986. A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have ...

The changes in humidity levels during the Diwali festivities have been examined over a period of 13 years at three Indian metro cities: Ahmedabad, New Delhi and Kolkata. A small short term increase in relative humidity even in the absence of transport ...

****"One of the standard rules (Stoke’s Law) applied in engineering calculations to estimate the suspension times of droplets falling under gravity with air resistance, was derived assuming several conditions including that the ambient air is still. So actual suspension times will differ and vary." "Although short-range large-droplet transmission is possible for most respiratory infectious agents, deciding on whether the same agent is also airborne has a potentially huge impact on the types (and costs) of infection control interventions that are required." "Despite the various mechanistic arguments about which organisms can be potentially airborne and therefore aerosol-transmissible, ultimately, the main deciding factor appears to be how many studies using various differing approaches: empirical (clinical, epidemiological), and/or experimental (e.g. using animal models), and/or mechanistic (using airflow tracers and air-sampling) methods, reach the same consensus opinion. Over time, the scientific community will eventually form an impression of the predominant transmission route for that specific agent, even if the conclusion is one of mixed transmission routes, with different routes predominating depending on the specific situations. This is the case for influenza viruses, and is likely the most realistic. Some bacterial and viral infections that have more than one mode of transmission are also anisotropic, like anthrax, plague, tularemia and smallpox: the ***severity of the disease varies depending on the mode of transmission** [37, 89]. Older experimental infection experiments on volunteers suggest that this is the case for influenza, with transmission by aerosols being associated with a more severe illness [14, 90], and some more recent field observations are consistent with this concept [57]. For anisotropic agents, even if a mode of transmission (e.g. aerosols) accounts for only a minority of cases, interruption of that route of transmission may be required if it accounts for the most severe cases."

Abstract. Annual influenza epidemics in the United States result in an average of >36,000 deaths and 114,000 hospitalizations. Influenza can spread rapidly

"The successful transmission of infection via the airborne route relies on several factors, including the survival of the airborne pathogen in the environment as it travels between susceptible hosts. This review summarizes the various environmental factors (particularly temperature and relative humidity) that may affect the airborne survival of viruses, bacteria and fungi, with the aim of highlighting specific aspects of environmental control that may eventually enhance the aerosol or airborne infection control of infectious disease transmission within hospitals."

1999