Philosophy is written in the great book
which ever lies before our eyes
– I mean the Universe-
But we cannot understand it if we do not first learn the language and grasp the symbols, in which it is written
Galileo Galilei (1623)
Galileo Galilei (1623)
Atmosphere is the blanket of gases and suspended solids and liquids that are held near to the earth mainly up to the height of 100 km from the sea level by gravitational force.
Role of the atmosphere
Earth’s atmosphere plays a vital role in regulating the temperature by providing a blanket of gases that not only protects us from excessive heat and harmful radiation from the sun that keeps us from being burned to death. It also traps reradiated heat from the earth’s surface and thereby keeping us warm and makes the Earth habitable. It helps to bring the rain and holds oxygen that we need to breath.
Heat or Thermal Energy: It is a form of energy that is transferred from a warmer body to a cooler body as a result of temperature gradient. Heat can be transferred by the process of Conduction, Convection and Radiation. When heat is transferred to an object, it increases the average kinetic energy (energy generated through movement) of the particles and therefore an increase in its temperature. Temperature can be considered as the measure of the average amount of kinetic energy of particles. As temperature increases so does the kinetic energy. The lowest temperature that can be attained theoretically in this universe is -273.15 degree C (the zero point at the Kelvin scale). At this temperature, all thermal energy is removed from the particles and the motion of the particles would be completely stopped.
Conduction, Convection and Radiation: Conduction is the transfer of heat energy by direct contact, convection is the transfer of heat by actual motion of matter; radiation is the transfer of energy by electromagnetic waves that does not require a medium. Unlike conduction and convection, radiation does not need matter to transfer heat and can be transferred in vacuum.
Thermodynamics: It is the study of energy and how it is interconverted. The first law of thermodynamics states that energy can be converted from one form to another and the total amount of energy in a given system will always remain constant. Earth’s energy budget also follows the laws of thermodynamics.
Albedo is the proportion of the radiation that is reflected by a surface. It is the measure of the reflective nature of an object means how reflective a surface is. The more reflective a surface is the higher the albedo value. Dark colour objects absorb most of the solar radiation and hence have a low albedo, whereas light-coloured ones have a high albedo, as they reflect most of the radiation. Ice and white clouds have high albedos. Albedo is also affected by Emissivity of an object. When electromagnetic radiation is incident on a surface, it is either absorbed causing the surface to get hot or it is reflected. The ratio of reflected to incident radiation is called Albedo. Reflectivity: the percentage of incident light or solar radiation that is reflected. Emissivity: the rate at which absorbed energy is radiated from an object. It is the ratio of the energy radiated by an object to the energy radiated by a black body of the same temperature.
0 to 1 scale (or in percentage): 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that reflects all incident radiation. The albedo for snow is 90% (0.9) since it reflects most of the radiation incident on it. On the other hand, a dark canopy forest has a low albedo of 10% (0.1).
Electromagnetic Radiation (EMR): Refers to the waves of massless elementary particles called photons propagating (radiating) through space, carrying radiant energy in the form of visible light, radio waves, specifically at shorter wavelengths. Electromagnetic spectrum (EMS) is a spectrum of wavelengths that comprise various types of electromagnetic radiation.
Short-wave and Long-wave radiation:
The Sun being a much hotter body emits most of its radiation in the shortwave end and the Earth in the longwave end of the spectrum. The division between shortwave and longwave radiation occurs at about 3 micrometers. The energy (E) of electromagnetic radiation is inversely proportional to the wavelength (λ). E = 1/λ
High energy radiation such as gamma and X-rays have small wavelength. Low energy radiation such as infrared radiations have long wavelength. Shortwave radiation is the radiant energy with wavelengths in the visible, near-ultraviolet, and near-infrared spectrum. It may be broadly defined to include all radiation with a wavelength of 0.1μm and 3.0 μm (Micrometer, also known as a Micron). Long–wave electromegnetic radiation lies in the wavelength range emitted by the surface and atmosphere at wavelengths between 3 and 100 μm. 1 micron = 1000000 of a meter.
Insolation and Heat budget: The total amount of radiant energy received from the sun on the earth surface is called insolation or incoming solar radiation. It varies from equator to pole ward, from season to season, even with in a course of a day. The net solar radiation received (as short wave radiation) by the earth and its atmosphere is converted into long wave infrared radiation after absorption and is sent back to the space. On an average, there exists a balance between the total energy received and the total amount of energy lost from the system of the earth and its atmosphere through this process. This is known as energy budget of the earth. Therefore, in the long run, there is a balance between the total amount of insolation received by the earth and its atmosphere to that with the total amount of radiation returned to the space.
Insulating blanket of the Earth: Greenhouse gases (GHGs) warm the Earth by absorbing energy and slowing the rate at which the energy escapes to space; they act like a blanket insulating the Earth. Two key ways in which these gases differ from each other are 1. their ability to absorb energy, and how long they stay in the atmosphere (Repose or lifetime).
The rough estimates: The annual balance of between incoming and outgoing radiation is the global energy budget, illustrated as 100 units or 100% of insolation received at the outer margin of the atmosphere. Most of the radiation that enters the atmosphere does not heat it directly. Earth and its atmosphere get heated by the process of greenhouse effect. About 31 units of total insolation are reflected or scattered back to the space. This bounced back radiation is called Albedo. Nearly 50% of the radiation pass through the atmosphere to the Earth’s surface and is absorbed, heating the surface. The heated earth then starts transferring energy to the atmosphere in a number of ways such as radiating long wave radiation, conduction, convection, latent heat of cloud formation etc. Greenhouse gases then absorbs large amount of energy and radiate it back to the surface. Humans are likely altering the energy balance of the earth and its atmosphere by enhanced greenhouse effect, popularly known as global warming.
Atmospheric Window: Some of this infrared energy is trapped in the atmosphere by H2O, CO2, and O3, and some passes through to space. Energy that has wavelengths ranging from 7 to 17 micrometers is not absorbed well by H2O vapor, CO2 and O3, and so it passes through the atmosphere and into space. This is known as atmospheric “window that allows the radiation to directly pass through.”
Earth’s average surface temperature is currently about 15 °C or 288K. If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below −40 °C. In contrast, if the entire Earth was covered by water, a so-called ocean planet the average temperature on the planet would rise to almost 27 °C.
0 K = -273 degree C AND 273 K = 0 degree C
Therefore to convert K (Kelvin) to degree C (celsius scale) add 273.
To convert degree C to K add 273.
Ozone is a pale blue colored, highly reactive gas composed of three oxygen atoms. It can be both natural and man-made and mostly found in the stratosphere roughly between 15 and 35 km above the Earth’s surface. Tropospheric ozone is mainly a pollutant. Ozone is both created and destroyed in the stratosphere. UV rays from the sun are absorbed by oxygen, splitting the molecule into single mono-atomic oxygen. These oxygen atoms then combine with oxygen molecules to form ozone. Ozone layer acts as a protective shield as it is very effective in absorbing the harmful UV radiation.
The Global Warming Potential (GWP): allows comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2). The larger the GWP, the more that a given gas warms the Earth compared to CO2 over that time period. Methane (CH4) is estimated to have a GWP of 28–36 over 100 years. CH4 also absorbs much more energy than CO2. Nitrous Oxide (N2O) has a GWP 265–298 times that of CO2 for a 100-year timescale. The GWPs for Chlorofluorocarbons (CFCs) can be in the thousands.
Many greenhouse gases occur naturally in the atmosphere, such as carbon dioxide, methane, water vapor, and nitrous oxide, while others are man-made. These include the chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and Perfluorocarbons (PFCs) etc. CFCs contribute to ozone depletion in the upper atmosphere. CFCs cause the breakdown of the ozone layer that protects the earth from the sun’s ultraviolet (UV) radiation.
Chlorofluorocarbons, that is, compounds containing Chlorine, fluorine, carbon, and hydrogen, have been used extensively in the industrialized nations in the past decades primarily as propellants in aerosol spray cans, as refrigerants ( link for the physics students), and as blowing agents in producing foam. Their chemical characteristics have made them ideally suited for such uses in that they are generally nontoxic and chemically inert. They are clear, colourless liquids or gases with slight ether like odor at high concentrations. Very low boiling point gives them the character of coolant as well as a lubricant. The breakdown of CFCs releases chlorine, which then acts as a catalyst for the destruction of the ozone layer. Ozone molecules form a layer in the stratosphere, 10 to 50 km above the Earth. This layer protects us from ultraviolet (UV) radiation and, in particular, from most of the ultraviolet B radiation (UVB). UVB is the main cause of sunburn and skin damage, and a decrease in ozone levels will result in more UVB reaching the Earth’s surface.
The Ozone Hole was discovered above Antarctica in 1985, highlighting the seriousness of the danger posed by the continued production of CFCs. Afterwards, the production of CFCs compounds has been phased out under the Montreal Protocol (1987) and they are being replaced with other products such as hydro-fluorocarbons or hydrocarbons. C-H bond is more stable than the C-Cl bond and does not breakdown at the presence of UV rays. However, most of the refrigerant including CFCs have relatively high ozone depleting potential (ODP) and high global warming potential (GWP). Click here to know more about the Antarctic Ozone hole from the educational blog of CIRES (partnership of NOAA and Colorado University research team).