Acute and chronic exposure on humans of carbon dioxide contained both in the air of enclosed spaces and in the atmosphere of the Earth are described. The current tendencies of increasing the CO2 content in the external and internal aerial environment of buildings are shown. A forecast of the consequences of an increase in the content of carbon dioxide in the atmosphere for human health is presented. The paper presents information on the technological systems created by the «Carbon Engineering» enterprise for cleaning the atmosphere from CO2, allowing to eliminate the accumulation of carbon dioxide in the air, regardless of the reasons causing the accumulation. The use of technologies of physicochemical and bio regeneration of the chemical composition of air and water is proposed to create an artificial environment favorable for humans.
1. Human exposure to CO2
Carbon dioxide plays an important role in the physiology of the human body, participating in the processes of cellular metabolism and regulation of the functions of external respiration. There are no permissible standards for the content of CO2 in the outdoor air since for a long time it was believed that carbon dioxide, the concentration of which in the atmospheric air in the pre-industrial era (before 1750) did not exceed 300 ppm (0.03% by volume), does not have any harmful effect on humans. The consequences of acute exposure to CO2, manifested when it accumulates above 5000 ppm in the air, began to be massively recorded only in the middle of the 19th century, when, with the beginning of the industrial revolution, a large number of people began to spend a long time in enclosed industrial premises with sources of carbon dioxide emissions (steam boiler furnaces, melting furnaces, coke oven batteries, etc.), the number of which increased rapidly due to the growth of the heat power industry, manufacturing, and transportation.
Problems associated with high levels of carbon dioxide in the air include nasal congestion, eye inflammation, nasopharyngitis, cough, headache, fatigue, and decreased concentration. When exposed to extremely high concentrations of CO2 (over 15000 ppm), there is a rapid accumulation of carbon dioxide in the human blood (hypercapnia), accompanied by an increase in blood acidity (a decrease in pH), which causes acidosis — acidification of the body formed by the interaction of CO2 with water molecules of carbonic acid H2CO3. The symptoms of acidosis are depression of the functions of the central nervous system, expressed in drowsiness, stupor (obtundation), and coma. When blood pH drops below 7.0, death occurs1.
In 1865, the German hygienist M. Pettenkofer proposed using the concentration of carbon dioxide as a criterion for the suitability of air for human breathing2. In 1964, O.V. Eliseeva found that even short-term inhalation of air with a CO2 concentration of 1000 to 5000 ppm causes noticeable changes in the respiratory system, blood circulation, and brain electrical activity3. Therefore, in most regulatory documents, 1000 ppm was taken as the permissible content of carbon dioxide in indoor air. However, in work4 it is noted that the average CO2 content, with a long stay of people in enclosed spaces, should not exceed 800 ppm. Only at this concentration the number of symptoms caused by poor air quality significantly reduced.
Currently, there is no unambiguous value limiting the permissible content of carbon dioxide in indoor air. Thus, the European standard prEN 13779: 2006 (E) for industrial and public buildings establishes 4 classes of air purity depending on the content of carbon dioxide5. The cleanest air of class IDA 1 should contain no more than 400 ppm CO2, and for the air of the lowest quality IDA 4 it is allowed to exceed the threshold value of 1000 ppm up to 1200 ppm.
It is also necessary to note an extremely important instruction for the developers of ventilation systems contained in the regulatory documents: «The permissible content of CO2 in premises is taken over the content of CO2 in the outside air.» Thus, the concentration of carbon dioxide in the internal atmosphere of buildings located in large industrial cities will significantly exceed 400 ppm, even with properly designed and well-functioning ventilation. The Russian standard GOST 30494-2011 recommends, during the calculation of the required performance of ventilation systems, to take the CO2 concentration in the outside air equal to 400 ppm for buildings located in the polluted center of a large city6. Therefore, the air of the 1st quality class in such premises can contain up to 800 ppm of carbon dioxide.
According to the results of the surveys given in work7, people in the enclosed spaces begin to feel signs of deteriorating air quality in the form of stuffiness already at a carbon dioxide content of 600 ppm. Therefore, air considered to be of high quality according to regulatory documents may in fact, not be such according to the subjective sensations of the people breathing it. Since ventilation is currently the only way to regulate the gas composition of the internal atmosphere of buildings, produced by air exchange with the environment, the condition of the outside air has a direct impact on the quality of indoor air.
Disadvantages of the current operation of buildings and ventilation systems can be added to the problem of outdoor air pollution: an increase in the estimated number of people in enclosed spaces, replacement of window frames with double-glazed windows, clogging or blocking of air ducts, etc. Article8 presents the results of measurements of the content of carbon dioxide in the air of various buildings and structures, according to which the concentration of CO2 in industrial premises at the end of the working day with inoperative ventilation can reach 2500 ppm, in residential apartments with double-glazed windows after a night’s sleep — 2000 ppm, in educational institutions to at the end of classes — 1500 ppm, in kindergartens — 700 ppm.
The currently emerging trend of deterioration in the quality of indoor air in the industrial, communal and residential environment has led to the widespread use of SBS — Sick Building Syndrome in many countries of the world9. People who spend a long time in “sick buildings” suffer from poor health. Due to poor air quality, they develop irritation and inflammation of the mucous membranes of the eyes, nasopharyngitis, rhinitis, throat irritation, dry cough, allergies, headache. There is also a decrease in working capacity and a decrease in attention concentration10.
SBS usually resolves after prolonged outdoor exposure. But apart from the tendency of deterioration in the quality of indoor air in premises, there is a tendency to an increase in the content of carbon dioxide in the atmosphere of the planet as a whole. Since a person breathes this air throughout his life, the task of studying the exposure to human health of CO2 contained in the outdoor air at relatively low concentrations is urgent.
2. Consequences of the increase of CO2 content in the atmosphere
Regular monitoring of the amount of carbon dioxide in the air began to be carried out in 1958 by the Mauna Loa observatory located in the Hawaiian Islands (USA) in the central part of the Pacific Ocean11, that is, away from large industrial land regions. According to the results of long-term observations, an increase in the average annual concentration of CO2 was recorded from 315 ppm in 1958 to 400 ppm in 201412. The problem of the accumulation of carbon dioxide in the atmosphere is currently receiving much attention, primarily in connection with climatic changes. Therefore, the Intergovernmental Panel on Climate Change (IPCC) carried out modeling of the global carbon cycle, taking into account the technogenic impact, and proposed four scenarios for a further increase in the concentration of CO2 in the Earth’s atmosphere. These forecasts are called Representative Concentration Pathways (RCP) and are denoted by the amount of additional contribution of carbon dioxide to radiative forcing to climate, which can be achieved by 2100, compared with the period before the start of the industrial revolution (1750). Scenarios RCP2.6, RCP4.5, RCP6 and RCP8.5 envisage an increase in the inflow of long-wave (thermal) radiation in the “surface-atmosphere” system by 2.6, 4.5, 6, and 8.5 W/m2, respectively13.
According to the most optimistic scenario (RCP2.6), the CO2 concentration in the Earth’s atmosphere will reach 450 ppm by 2060 and decrease to 421 ppm by 2100. The most pessimistic forecast (RCP8.5) assumes an increase in the carbon dioxide content to 936 ppm at 2100, after which the increase in the concentration of CO2 in the atmosphere will continue at the same rate14. However, since priority attention is now given to changes in the global climate, the problem of the direct and immediate impact of an increase in the content of carbon dioxide in the atmosphere on health remains underestimated by researchers. Man, as a biological species, was formed under conditions when the concentration of CO2 in the air never exceeded 310 ppm but did not decrease to less than 180 ppm, as was established based on studies of air bubbles frozen in the ice of Antarctica for more than 400 thousand years15.
It is possible to assume that the increase in the content of carbon dioxide in the planet’s atmosphere observed over the past 60 years has an impact on the entire population of Homo sapiens. D.S. Robertson in article16 showed the relationship between changes in the acidity of a person’s blood and the concentration of carbon dioxide in the inhaled air during lifelong exposure. As already noted, a change in the pH of human blood even by 0,1 units entails significant shifts in the work of physiological systems. In this way, the homeostasis of the body tends to compensate for the resulting acidosis.
K.E. Schafer studied the chronic exposure of carbon dioxide, based on medical examinations of submariners who were continuously exposed to elevated concentrations of carbon dioxide for a long time17. It was found that an increase in the content of CO2 in the air significantly changes the biochemical indicators of the blood. Carbon dioxide has been recognized as a major component of the environment with rapid, direct exposure to human health. The formation of carbonic acid in the blood leads to the extraction of calcium and phosphorus from the bones with the formation of bicarbonates of these chemical elements. Bicarbonates are excreted from the blood by the kidneys, and at very high concentrations, they are deposited in the bones, kidneys, liver, and lungs of a person in the form of pathogenic biominerals — calcifications.
Data obtained by D.S. Robertson on the increase in blood acidity, due to an increase in the concentration of CO2 in the atmosphere is confirmed by the results of population medical studies of the US population, given in the review18. The increase in the number of bicarbonates in the blood serum from 23,7 mmol/L in 2000 to 25,2 mmol/L in 2012 indicates the compensation of mild forms of mass acidosis. In addition to the fact that acidosis compensation leads to multisystemic damage to the human body caused by calcification deposits, other long-term health exposures of elevated carbon dioxide levels have been identified. A study19 provides data that even a small increase in the concentration of CO2 in the inhaled air with prolonged exposure to humans can cause endocrine dysfunctions of the thyroid gland associated with a decrease in the content of free calcium in the blood, which leads to pathologies of intrauterine growth, leading to miscarriages during pregnancy and the birth of dead children.
These health disorders can negatively affect the entire population so that a further increase in the concentration of CO2 in the Earth’s atmosphere could call into question the survival of mankind. According to D.S. Robertson, the critically low value of the acidity of human blood pH = 7,3 with a further decrease of which develops acidosis, corresponds to a concentration of carbon dioxide in the air equal to 426 ppm. Even under the most optimistic scenario (RCP2.6), this carbon dioxide content will be reached by 2050. Therefore, the task of reducing the concentration of CO2 in the atmosphere is extremely urgent, not only in the light of preventing climatic changes but also from the standpoint of preserving the chemical composition of the environment suitable for human life.
3. Technological removal of CO2 from the air
At present, great efforts of the world community are aimed at limiting carbon dioxide emissions into the atmosphere, primarily through the transition to the use of unconventional energy sources (solar, wind, geothermal, tidal, etc.), replacing the capacities of traditional thermal energy. However, this path is not a universal way to reduce the concentration of CO2 in the Earth’s atmosphere in general and in the internal air environment of buildings and structures in particular. There are alternative technical solutions, which receive much less attention both in the mass media of the population and in the scientific, political, and business communities.
Firstly, a reduction in the supply of technogenic greenhouse gases, and primarily carbon dioxide, may be ineffective if the increase in the concentration of CO2 in the atmosphere has natural, rather than anthropogenic, causes. This point of view is expressed by many scientists20. Secondly, if the model of the technogenic impact on the climate turns out to be correct and the global economy can ideally reduce the emissions of greenhouse gases to almost zero, then the problem of excess carbon dioxide accumulated in the atmosphere will remain, it can continue to negatively affect not only the planet’s climate but also on human health.
Another aspect of disrupting the carbon cycle, in addition to direct CO2 emissions from the energy sector, industry, and transport, is the reduction of the functions of the biosphere for the utilization of atmospheric carbon dioxide due to damage to regional ecosystems by human economic activities (agriculture, deforestation, mining, solid waste storage, etc.). Carbon dioxide simply has nowhere to go out of the atmosphere, since the global shortage of ecosystem services, (including the World Ocean), to maintain a favorable chemical composition of the air is now estimated21 to be about 5%. That is, with the total amount of organic compounds removed from the air by terrestrial and aquatic ecosystems of 172 Gt/year (in terms of pure carbon), 8,6 Gt/year of such substances, primarily CO2, remain in the atmosphere. Of these, the share of emissions from the combustion of fossil fuels accounts for 6 Gt/year, and the remaining 2,6 Gt/year are formed due to the disturbance of ecosystems during land use and forest use. Thus, in the campaign to reduce CO2 emissions, not enough attention is paid to the fact that only one reduction in direct greenhouse gas emissions by the economy, without changing the principles of environmental management, can reduce the global imbalance of the carbon cycle by no more than 70%, which will not solve the problem already accumulated in the atmosphere of carbon dioxide.
It is possible to propose the following ways to reduce the CO2 content in the air, which every inhabitant of the Earth breathes for a long time.
1. Organization of technological removal of carbon dioxide directly from the atmosphere or directly from sources of its emissions using technical air purification systems.
2. Creation of a closed artificial habitat using technologies for the regeneration of the chemical composition of air and water necessary for a person.
To implement the first method, new groups of technologies are currently being developed, which are named22 «Carbon Capture and Storage» (CCS). They are based on the processes of CO2 adsorption on zeolites. A technological installation for cleaning the atmosphere from excess carbon dioxide should have fans for pumping air, a dehumidifier that removes water vapor, an adsorber that captures carbon dioxide, a desorption system by heating zeolites, and storage for the captured gas. CO2 accumulated in the tanks can be further used for various purposes. The Canadian company «Carbon Engineering», 30 miles north of Vancouver, has built a plant to extract carbon dioxide from the atmospheric air23. The captured and concentrated carbon dioxide is converted into biofuel, methane, through a hydrogenation reaction. «Carbon Engineering» is currently planning to build the world’s largest carbon dioxide removal plant, capable of pumping 500,000 tons of CO2 out of the air every year. The installation will be located in Texas (USA).
This method is a universal solution to the problem of increasing the concentration of carbon dioxide in the atmosphere and climate change, regardless of the cause — natural or anthropogenic. But the project to remove CO2 from the atmosphere in the required quantities (up to 10 Gt/year) requires extremely large expenditures of time, material, and financial resources, therefore, it can be completed promptly only under the most optimistic scenario of changes in the gas composition of the atmosphere and climate (RCP2.6).
In the case of a more rapid increase in the concentration of CO2 in the atmosphere (RCP8.5), established by D.S. Robertson, the critical value of 426 ppm will be reached by 2030, after which there will be mass diseases of people caused by the consequences of acidosis. To solve this problem, it is possible to propose to implement a project of transferring the production and living environment to the principle of closed internal gas exchange, water flows, and solid matter recycling. Then the regeneration of the chemical composition of air and water necessary for a person will be carried out using physicochemical methods.
For this purpose air and water purification technologies based on various physical and chemical processes as well as with the help of biotechnologies can be applied. The main problem of creating a closed artificial habitat is its energy supply. Due to the need to move away from traditional thermal energy, it is important to develop projects that allow more efficient utilization of the energy of the sun, air, water, and biomass. Thus, the heat obtained from various sources — from solar radiation, heated air, and water, decomposing organic matter can be used to generate electricity using a universal thermal machine, such as a Stirling engine, or other devices. The theoretical calculation and experimental study of heat and mass transfer processes occurring in such devices are given much attention in Bauman Moscow State Technical University24, 25, 26, 27.
At present, experimental technologies have been developed for the bio regeneration of air and water in enclosed spaces using higher plants, microalgae28, 29 and other microorganisms30, 31, 32, 33 which can also be intensified, for example, by ozonation34. Technologies planned to create artificial ecosystems for future extra-terrestrial colony35, may find applications on Earth today. This path will not prevent further climatic changes but will ensure the survival and development of the human population under any possible negative scenarios of changes in the chemical composition of the planet’s atmosphere and hydrosphere.
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Yu L Tkachenko1, a), S D Morozov1, I S Sherbakova1, A S Rovnyagina1,
1 Bauman Moscow State Technical University, Moscow, 105005, Russia