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TECHNICAL SCHEME

The primordial atmosphere
Today, our atmosphere is composed of about 21% of oxygen, 78% of nitrogen, and 1% of small quantities of various gases: argon, neon, hydrogen, etc. But it has not always been so! It is estimated that Earth's primordial atmosphere - about 4.5 billion years ago - was mostly composed of hydrogen, nitrogen, carbon dioxide (CO2), ammonia (NH3) and methane (CH4). No oxygen, therefore! Or in very small quantities, of the order of only 0.0001%.
Therefore, we are talking about the absence of O2 gas , at that time.  Paradoxically, the oxygen atoms were  all there, and they were  even among  the most abundant elements on earth. But for the most part they were linked to carbon to form CO2 or trapped in rocks of the crust and mantle.

All this changed with the appearance of life about 3.5 billion years ago. A key element of life as we know it, is the ability to produce organic carbon molecules (such as carbohydrates, proteins or lipids), which serve as sources of energy. To make them, living organisms have to find carbon. The first bacteria found their carbon by picking up what came within their reach as nutrients (humans do the same). But about 2.7 billion years ago, a new type of bacteria appeared: cyanobacteria.

Cyanobacteria were the first to invent photosynthesis as we know it. From CO2, water and solar energy, these bacteria - sometimes also called blue-green algae - were able to capture the carbon in the CO2, while rejecting oxygen! Unlike plants (which convert mineral nitrogen into organic nitrogen) and animals (which convert organic nitrogen into another organic nitrogen), cyanobacteria (and a few others) are able to take nitrogen directly into the air, gaseous form, and turn it into organic nitrogen. They thus put 100 million tons of mineral nitrogen a year at the disposal of plants on the planet.
Cyanobacteria, which make up a good part of phytoplankton, contribute significantly to the surface fixation of oceans, atmospheric carbon dioxide (CO2). This role is of major importance today because of the increased production of this greenhouse gas by human activities.
As an essential link in oceanic food chain, they contribute greatly to the transformation of CO2 into carbon (the organic pump) and its storage in deep ocean sediments (carbon sinks), in reserve for the future needs of the planet.

Air Composition
Dioxygen, O2: 20.9476%
Nitrogen, N2: 78.084%
Argon, Ar: 0.934%
Carbon dioxide, CO2: 0.0314%
Hydrogen, H2: 0.000 05%
Neon, Ne: 0.001 818%
Helium, He: 0.000 524%
Krypton, Kr: 0, 000 114%
Xenon, Xe: 0.000 008 7%


The measurement of oxygen content in inhaled air is fundamental to health, (as well as we measure the various primary pollutants: oxides of carbon, sulfur, nitrogen, VOCs, PM10 and PM2.5 particles , metals or light hydrocarbons and ozone), the constant must be 21%.

The combined action of land and oceans on atmospheric oxygen
Photosynthesis, respiration and dissolution in seawater act simultaneously and vary the concentration of oxygen in the atmosphere. These variations were measured by Keeling and Shertz (1992) in three places on the planet: Alaska, California and Tasmania. In the first two, both located in the northern hemisphere, there is a maximum of atmospheric oxygen in summer and a minimum in winter. The summer maximum is mainly due to the photosynthesis on the land surface that characterize this hemisphere. In winter, breathing and dissolving in the colder sea water combine to give rise to a minimum. Between maximum and minimum, the difference is approximately 26 ppm (parts per million) in Alaska, and 20 ppm in California. This difference is smaller in Tasmania (18 ppm), the southern hemisphere being mainly occupied by the oceans and terrestrial photosynthesis only plays a small role. These seasonal variations are very small compared to the oxygen concentration of about 200,000 ppm. The highest, that observed in Alaska, represents only 0.013%. Even a small change in the oceans balance , or global photosynthesis (even in the case of the Amazon, the so-called "lung of the planet"), could threaten the quality of the atmosphere in the medium term.

Human disturbance

For more than a century, man has been meeting his energy needs by burning coal and hydrocarbons from photosynthesis of past geological eras. This combustion consumes oxygen. Similarly, the increase in the world's population has led to the clearing of forests and replacing them with crops. This practice also results in oxygen consumption. On one hand, the biomass that constitutes the forest, very high, is largely transformed into carbon dioxide. On the other hand, agricultural practices generate an impoverishment of the soil by degradation of the organic material they contain (humus). This degradation is caused by organisms that breathe and therefore consume oxygen. The corresponding decreases are in total at the rate of about 4 ppm / year or about 0.002% of the oxygen content of the atmosphere.
Again, there are reasons to fear a lack in the decades to come, as the emissions of carbon dioxide by the man continue to increase every year .

Oxygen tends to associate with other chemicals to oxidize (burn). Thus, stocks of carbon or organic matter that do not currently participate in the living matter cycle could "go up in smoke" by incorporating oxygen. Soil organic matter is an example as we saw above when forests are cultivated. Oxidizable carbon stocks are available in the Geneva based 5th IPCC ( Intergovernmental Panel on Climate Change )report. Knowing that an oxidized carbon atom in a carbon dioxide molecule consumes an oxygen molecule, a rapid calculation gives, in case of rapid global oxidation of these stocks, the following orders of magnitude (percentages of decrease in atmospheric oxygen):
oxidation of hydrocarbons (gas) - 0,19% oxidation of hydrocarbons (petroleum) - 0,07% oxidation of coal - 0,16% oxidation of organic matter of soils - 0,64% oxidation of permafrost - 0,55%
Oil, gas and hydrocarbons, if they pose a threat to the climate, can therefore cause, in the case of intensive mining, a decrease in the oxygen concentration of the atmosphere.

According to a study of the INRS "National institute of research and security" on Confined Spaces, the measurement in oxygen content in a confined or polluted space must be controlled: Measure Oxygen Content Together, the oxygen content of the ambient atmosphere will be monitored using a portable oxygen meter. If the oxygen content is less than 19%, penetration should only be carried out with respiratory protective equipment. It should be noted that any measured oxygen concentration below 20.5% already reflects
an anomaly in the atmosphere of the confined space (oxygen consumption or accumulation of another gas).

Creation of a roof top garden laboratory and micro algae greenhouses

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