COMPOSITION OF AIR (ATMOSPHERE)
The composition of air (or the atmosphere), as known today, is a mixture of different gases (near the surface of Earth):
- nitrogen (N2: 28 gm/mol) (78%);
- oxygen (O2: 32 gm/mol) (21%);
- argon (Ar: 40 gm/mol) (0.9%);
- carbon dioxide (CO2: 44 gm/mol) (0.04%);
- water (H2O: 18 gm/mol) (vapor) (traces);
- other gases (hydrogen, etc.) (traces).
The global average temperature of the Earth is primarily regulated by the heat received from the Sun (Appendix C). Furthermore, the energy (heat, radiation) reaching the Earth from the Sun has to pass through the atmosphere surrounding the Earth. This means that the sun’s energy (radiation) has to interact with
- gas molecules (and dust particles) in the air (atmosphere)
- reflection by air/clouds
- reflection from Earth, trees, and ocean surface
The heat from the Sun (the surface temperature of the Sun is 5500°C) is transmitted by the infrared wave length of the radiation. The infrared is absorbed by some gases found in the atmosphere (e.g., carbon dioxide, methane, etc.). These gases are called greenhouse gases (GHGs). The absorbed infrared energy is reflected in all directions, which increases the temperature of the planet Earth. In the present text, there is only interest in carbon dioxide and its interactions with the temperature balance of the Earth.
The concentration of carbon dioxide (CO2) in air is reported to be increasing over the past century (ca. 2 ppm/year) (IPCC, 1995, 2005a, b, 2007, 2019; IEA (International Energy Agency) 2011, 2012, 2013, 2014a, b, c, 2015a, b, c, d, 2016e; EPA Handbook, 2011; Dubey et al., 2002; Sanz-Pérez, 2016; Rackley, 2010; Dennis, 2014; CSIRO, 2013; Albo et al., 2010; Oh, 2010; Hinkov et al., 2016). This has been attributed to fossil fuel burning (combustion) (anthropogenic CO2) (Leung et al., 2014; McDonald et al., 2015). Furthermore, the increase in population and increased energy demand leads to increase in anthropogenic CO2.
This book relates to the carbon (i.e., CO2) capture and surface chemistry properties of carbon dioxide (CO2), especially its connections to the change in temperature (average temperature) of Earth. However, it is useful to describe some general remarks about the atmosphere (air) and its characteristics.
The composition (and temperature and pressure) of air varies with height over Earth. In other words, when one considers the composition of air, the height has to be considered. The gradient of composition of air (i.e., variation of composition with height) might be dependent on time scale (and space). Similarly, water (e.g., oceans, rivers, lakes, drinking water) contains different salts (sodium, calcium, chlorides, sulfates, etc.) that are known to interact with some components of air (for example, carbon dioxide, oxygen). Mankind has been aware of the essential role played by these elements for the existence of life on Earth. Even though millions of miles away, the Sun provides heat to the Earth. Besides heat, the Sun also emits other kinds of energy to Earth, for example, radiation, ultraviolet light, and so on. The atmosphere surrounding the Earth has four distinct layers (Saha, 2008; Lang, 2006):
- 0 to 10 miles (0 to 16 km: temperature range, ca. 20°C to −50°C) TROPOSPHERE: This is the region of human activities.
- 10 to 30 miles (16 to 50 km: temperature range, ca. −50°C to 0°C) STRATOSPHERE: The ozone gas (O3) layer, which absorbs the ultraviolet (UV) radiation from the sun, is found in this region. The temperature is higher at higher altitude, owing to the absorbance of ultraviolet radiation from the Sun.
- 31 to 53 miles (50 to 80 km: temperature range from ca. 0°C to 90°C) MESOSPHERE: In the mesosphere, the temperature decreases as altitude increases.
- 53 to 75 miles (80 to 200 km: temperature from ca. >90°C) THERMOSPHERE: In this region temperature increases with altitude, owing to absorption of highly energetic solar radiation.
This clearly shows the complex sun—atmosphere system and the interactions relating to temperature on the Earth.
Further, mankind has used fire (with respect to food, combustion processes, energy (electricity, mechanical), transportation) in many different applications and technologies (both directly and indirectly) for many hundreds of years. It is also recognized that all these elements are essential for the existence of life on Earth. Fire or combustion of fossil fuels in the modern age is described as
- COMBUSTION: FOSSIL FUELS + OXYGEN (FROM AIR) = FIRE (heat, electricity, mechanical energy, etc.) (CO2 produced)
This process (i.e., the production of carbon oxide) is anthropogenic and is currently related to the world population (e.g., food and energy demands). It is thus seen that the above process of combustion adds CO2 to the air. At the same time, it must be stressed that carbon dioxide in air is essential for the existence of life on Earth.
PHOTOSYNTHESIS AND CARBON DIOXIDE CYCLE
The most significant process with regard to life and all kinds of living species on the Earth is the supply/production of food. The latter is singularly provided by the complex system that is dependent on the photosynthesis process (Paoletti et al., 2002; Raschi et al., 2000):
- CARBON DIOXIDE (CO2) + SUN SHINE + WATER < PHOTOSYNTHESIS > ALL KINDS OF PLANTS/FOODS/CARBOHYDRATES
Each gas component in air is known to have a specific role in the life cycle on Earth. For example, even though the concentration of carbon dioxide (CO2) in air is at present only 400 ppm (0.04%), it provides all carbonaceous food to life. Food is obviously the most necessary product for the existence of life on Earth. Actually, the photosynthesis process is the opposite of fossil fuel combustion, and CO2 is captured in plants and so on. It is important to mention that all the carbon atoms in plants on Earth are supplied by the CO2 in air (via photosynthesis). Furthermore, the food is digested by all living species on Earth by the metabolism process (Appendix C):
- The CO2—food—metabolism cycle:
- CO2 in air (photosynthesis) >>>> Food >>>> Metabolism (exhale CO2)
This shows that in the life cycle on Earth all the carbonaceous components are solely provided by CO2 in the air (EPA Handbook, 2011). Actually, it is clear now that all these natural elements are interrelated and are basic necessities for life on Earth. The characteristics of the different gases in air (atmosphere) for example:
- Oxygen (O2: 21% in air) is essential for all living species (as a source of metabolic and other reactions, for example, oxidation)....
