Ecology: Biology of Interaction. V-12. Absorption of Solar Radiation by the Atmosphere and the Greenhouse Effect

V-12. Absorption of solar radiation by the atmosphere and the greenhouse effect The atmosphere is selectively permeable to different parts of the electromagnetic radiation spectrum. Ionizing radiation and most of the ultraviolet radiation are effectively absorbed by the ozone layer (a zone of the atmosphere with a high ozone content - O 3 ), and the spectral region from infrared to short-wave radio radiation is absorbed by water vapor, carbon dioxide, methane, and other greenhouse gases. The absorption of ultraviolet and ionizing radiation by the atmosphere is primarily associated with ozone and, to a lesser extent, with oxygen. Under the influence of ionizing radiation, an oxygen molecule (O 2 ) can break down into atomic oxygen, which, by combining with other oxygen molecules, forms ozone (O 3 ). Ozone is a gas that is sometimes found on the planet's surface. It is responsible for the smell of "freshness" after a thunderstorm. It can be detected near switched-on ultraviolet lamps, as well as near faulty laser printers and copiers. On the Earth's surface, ozone is a dangerous pollutant. It is a much stronger oxidizer than oxygen, and therefore can damage living cells, causing, for example, lung cancer. Interacting with other pollutants in the lower atmosphere, ozone can make their effects much more dangerous. In the upper layers of the atmosphere, ozone acts as a screen, protecting the Earth's surface from hard radiation - the same radiation that causes its formation from diatomic oxygen. At altitudes from 12–25 to 45 kilometers above the Earth's surface, a layer with increased ozone content (with a concentration of about 0.001%) is formed. This layer effectively blocks ionizing radiation from the far ultraviolet with wavelengths less than 315 nm to gamma radiation. Each component of the atmosphere has its own, quite complex, absorption spectrum. Nevertheless, all together they cut out two regions from the solar spectrum (which also has a very complex frequency distribution). As a result, mainly visible light, as well as near (to visible light) ultraviolet and near infrared radiation, reach the Earth from the Sun (Fig. V-12.1). Fig. V-12.1. Main parts of the solar radiation spectrum on Earth. The gases that primarily absorb certain parts of the solar spectrum are indicated. Thus, most of the solar energy reaches the Earth in the form of visible light. Do you think that we see precisely these frequencies of the EMV spectrum is a coincidence or a completely logical result of our adaptation to the environment? In addition to the atmosphere, solar radiation is intensely absorbed in the hydrosphere and lithosphere. In water, the spectrum narrows significantly, and the amount of light reaching the depth decreases. Light practically does not penetrate the lithosphere. As already noted, the maximum solar radiation lies in the visible part of the spectrum (wavelength about 0.5 μm), and the Earth's surface - in the far infrared (about 10,000 nm). The reason for this difference is very simple: the Sun is much hotter than the Earth. The Earth's atmosphere transmits solar and terrestrial radiation differently: it is almost transparent to visible light, but effectively retains far-infrared radiation. As a result, energy passes more easily to the Earth's surface than it leaves it. The Earth heats up as a result. This phenomenon is called the greenhouse effect. The property of transmitting visible radiation better than infrared is possessed not only by air but also by many other substances - for example, glass and polyethylene film, which are used to cover greenhouses and hotbeds (Fig. V-12.2). Fig. V-12.2. The mechanism of a greenhouse's operation The greenhouse effect is one of the conditions for the existence of developed life on our planet. Without it, the average surface temperature of the Earth (which is about +15°C) would be –23°C, and the planet would be practically unsuitable for life (see section V-5). Water vapor, clouds and fog, atmospheric aerosols, carbon dioxide, and methane have greenhouse properties. Ultimately, the arrival and departure of energy from the Earth balance each other (otherwise the planet's temperature would not remain constant). But since the outflow of heat from the Earth's surface is hindered by the greenhouse effect, its sufficient level is achieved at a higher temperature than would be observed without this phenomenon.