Dear Alex,

This is indeed an interesting question, I also have been thinking about for years, but never tackled due to lack of physical expertise.

However, I do miss in your excellent paper a discussion about the robustness of the respiratory tract, in which dry/cold conditions lower the mucous layer thickness and at the same time the mucociliary clearance, especially among elderly people. This desiccation process, thus, results in a respiratory tract more vulnerable to exposure of various kinds, including virus.

Further literature for your convenience:

Moriyama M, Hugentobler W J and Iwasaki A (2020) Seasonality of Respiratory Viral Infections. Annu Rev Virol 7:2.1-2.19.

Wolkoff P (2018a) Indoor Air Humidity, Air Quality, and Health - An Overview. Int J Hyg Environ Health 221:376-390.

Wolkoff P (2018b) The Mystery of Dry Indoor Air - An Overview. Environ Int 121:1058-1065.

Kind regards,

Peder

Dear @Peder,

Thank you for the question!

The problem that you touched on is one of the most actual. Due to the strong word limit, this issue like many others was excluded from the manuscript. We have discussed this issue with specialists in the transmission of influenza and other respiratory infections at specialized conferences many times. I added some comments from this discussion at the end of this post.

Moreover, recently I pointed out the problem of dry mucosa in the elderly in a short message on the link: https://www.researchgate.net/publication/340006233_Supersaturation_in_the_Airways_and_Covid-19_New_Way_to_Understand

One of the main points is that the supersaturation and enhanced condensation of water vapor (as well as enhanced deposition of inhaled pollutants due to supersaturation) is a strictly localized process in the nose and upper airways.

This process occurs due to the mixing of air and mass transfer with the wet walls of the respiratory tract. If the mucous membranes of the walls of upper airways are dry (as in the elderly), then due to a violation of mass transfer with the walls, the localization of “Supersaturation” will shift to the lower section of airways.

Accordingly, the enhanced deposition of inhaled pollutants and infectious aerosols, as well as the physicochemical impact of the effect of supersaturation (pH of formed droplets under supersaturated conditions are 4.5-6.5), will affect the trachea and bronchioles in the elderly.

I believe that this may be one of the important factors for explaining the increased mortality among the elderly in Wuhan and Italy, where extreme levels of air pollution PM2.5 were observed at the same time. A few simple experiments could clarify this aspect, but unfortunately, my research is not of interest in Russia, so I can’t have a job, a salary, a laboratory and hire students.

Kind regards,

Alex

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Some points from previous discussions:

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Few words about physics of the supersaturation and cold dry air inhalation

On the one hand, a temperature difference of more than 20 degrees Celsius between the inhaled air (T100%) for a few milliseconds. Then, due to mixing with dry inhaled air, the RH in mixed air decreases to normal values below 100%.

Thus, evaporation will occur as well as condensation, and this will have the same impact (because evaporation and condensation are the same processes which are described by one physical law) but spaced apart by a few milliseconds with condensation during inhalation.

It follows from Table 1 that even a few milliseconds under the short-term supersaturated condition in the airways is enough for efficiently grow due to condensation of inhaled submicron particles to droplets of micrometer sizes and their subsequent enhanced deposition in the trachea and head airways until evaporation begins/starts.

PS

The localization of enhanced aerosols deposition in the elderly may be shifted in the lower airways due to the problem with “Dry Mucosa” (See below the text of the message )

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Indoor air and heated dwellings

This is an interesting question and an important point for future research. I think that this question touches on not only the problem of localization of enhanced deposition of submicron aerosols but also on a number of additional research concepts. It is obvious that the problem of timing and the strength of outbreaks of influenza and respiratory infections is the result of many factors as indoor temperature and humidity, crowding and close contact with other people, indoor air heating, vitamin deficiency, etc. And all these factors must be considered together.

The relative humidity (RH) of indoor air in heated houses and buildings in cold seasons may reach critically low values. However, indoor conditions correlate strongly with ambient outdoor conditions (Nguyen et al., 2014). People in industrialized countries generally spend more than 90% of their time indoors (Hoppe and Martinac, 1998), and such factors as indoor space temperature and humidity are important and especially for the elderly population.

Such “extreme” (and even normal indoor conditions) cannot be associated with supersaturation in the airways and enhanced aerosols deposition (as follows from Table 1 - see the main paper). However, exposure to dry conditions over a prolonged period of time leads to the suppression of host defense mechanisms (the mucous membrane layer dries and this can cause damage to the cilia, inhibiting the clearance in the airways). On the other hand, this may lead to a shift of normal localization of deposition of inhaled pollutants to the lower airways, since the ability of the upper airways to condition and filter air is impaired in this case.

Apparently, many factors which are typical for mid-latitudes and not typical for the tropics and subtropics (heating seasons, dry indoor air, vitamin deficiency, etc.) may be more likely to be associated with the strength of epidemics in the mid-latitudes than with the timing of influenza seasons in the different climatic conditions.

Thus, One of the most important findings is that the supersaturation effect can be clearly correlated with the timing of influenza in different climatic conditions. Perhaps, the Supersaturation is the only factor that can be used for analyzing the timing of influenza in mid-latitudes and tropics at the same time.

@Supersaturation/oversaturation definitely is unusual and generally neglected effect that can be induced in the airways by cold air inhalation (T70%; T

Preprint Age- and gender-related changes in the upper airways correla...

Effects of air pollution is definitely underestimated. There're many more aspects to consider.

And if we are wrong and the Earth is flat and it is the Sun that revolves around the Earth ?: The data and evidence on its harmful and pathogenic effects are so abundant that it is already something OBVIOUS ... and the obvious is not discussed! ; It is already something paradigmatic. CAN DATA AND EVIDENCE BE PRESENTED THAT CAN ALLOW A HYPOTHESIS ABOUT THE OPPOSITE ?; no Paradigm, ne the Theory of Knowledge, Epistemology and Philosophy of Science is changed for another unless there is no IRREFUTABLE AND CONTRACTABLE DATA THAT ALLOWS THE ESTABLISHMENT OF ANOTHER PARADIGM.

Hi, Francisco Javier Gala .

Indeed, in order to change the paradigm, we need to do a lot of work and present new evidence.

BUT the problem with assessing the deposition of inhaled particles (air pollution) inside the respiratory tract is that there is only one small inaccuracy in the right methodology - which is correct, well-developed and repeatedly tested and verified

... BUT all actions with this methodology was and is for normal external conditions (room temperature - normal humidity, etc.) - BUT we all know perfectly well that normal conditions on the street are often replaced by abnormal ones! == AND HOW DOES THE STANDARD METHODOLOGY TAKEs it INTO ACCOUNT?

- - - In my publication I showed - that a small assumption and simplification in standart methodology of estimating particle deposition (namely, that the initial conditions are always taken as NORMAL room conditions -- this asssuptation was was made in all models and is directly indicated ) is not true for cold and humid climates -

And THIS small assumptions can lead to significant errors in the estimates!

I am not trying to change the physical paradigm in the particle deposition model - I just showed - that this old paradigm needs the correct use of initial conditions --- if a person breathes cold air - or humid air - then these conditions should be reflected in the physical and mathematical model (heat and mass transfer within the respiratory tract is very important for the deposition of particles - As I Showed in my article) - - we must revise the standards adopted centuries ago in accordance with the latest scientific data.

@ The effect of super-saturation in the airways @ is a very important physical process that must be considered and taken into account by us!

Thank you, dear Alex N.