**5. Global warming potential**

Carbon di oxide is considered to be the knob of earth's thermostat and it is an amazing tracer gas. Even a small change in the Co2 concentrations makes a big difference to the global surface temperature [3]. Greenhouse gases have the properties of active radiative or heat-trapping nature. Comparing the properties of greenhouse gases, are done by indexing them according to their Global Warming Potential. The ability of a GHG to trap heat in the atmosphere comparative to an equivalent quantity of carbon dioxide is called GWP. Carbon dioxide has the value one (1), though the most prevalent, is the least powerful GHG. So, the greenhouse gases are expressed in carbon dioxide equivalents. The unit of GWP potential is million metric tons (MMTCDE) of carbon dioxide and greenhouse gas emission from an electrical appliance can be calculated by using the formula,

> Hours � No*:*of days � Watts <sup>1000</sup> KWh KWh � Emission factor ¼ Kg of Co2

Earth's life is protected from sun's harmful UV rays by ozone layer which is formed as a thin layer in the stratosphere. Ozone layer depletion was identified by the scientists during 1980. As a result of this, depletion of earth is likely to receive more amount of UV radiation, so that there is a strengthened chance of overexposure to UV radiation and the subsequent wellbeing effects. The below **Figure 1** depicts the formation and destruction of ozone depletion process. The sun's yield of UV B does not change. It is obvious that, less ozone means, more exposure of UV B radiation from the sun. The amount of UV B measured at the surface of Antarctic poles is two times during the annual ozone hole.

#### **5.1 Mechanism of ozone depletion by CFC's**

Ozone layer is destroyed in the stratosphere 15 to 20 Km directly above the earth surface by CFC's. Ozone concentrations are measured in Dobson units. 1 Dobson unit denotes 1 ozone molecule for every 1 billion air molecules. The meaning of ozone hole is the loss of ozone in a particular area. Greatest ozone hole is recorded in Antarctica continuously. The characteristics of ozone are, it is an allotrope of oxygen, and it is deadly to human beings if it is inhaled [4]. Human beings existence in the earth is very important and this is ensured by the protective layer ozone, as it filters or captivates ultra violet radiations which are usually short in wave length (280 – 320 nm). Ultra violet radiations can cause serious problems to humans such as sun burns, skin cancer, and eye disorders.

$$\begin{pmatrix} \begin{matrix} \begin{matrix} \begin{matrix} \mathbf{F} \end{matrix} \mathbf{R} \mathbf{M} \mathbf{A} \mathbf{T} \mathbf{I} \mathbf{N} \mathbf{N} \\\ \begin{matrix} \mathbf{0}\_{3} \rightarrow \mathbf{0}\_{2} + \mathbf{0} \end{matrix} \end{pmatrix} & \begin{matrix} \begin{matrix} \mathbf{0}\_{\text{ESTRUCION}} \\\ \begin{matrix} \mathbf{0}\_{3} + \mathbf{0} = \mathbf{2} \ \mathbf{0}\_{2} \end{matrix} \end{pmatrix} \end{pmatrix} \end{pmatrix}$$

**Figure 1.** *Ozone formation and depletion process.*

One of the chief characteristics of Chloro flouro carbons is, they do not dissolve in water and highly inert to water solubility. That is the reason they are not destroyed or dissolved even during in rain and stay in the atmosphere for many years and move slowly towards the stratosphere. The chloro flouro carbon molecules split off into chlorine atoms from the CFC molecules when they come in to contact with the ultra violet rays. The primary split of the CFC molecules are shown in the below equation.

$$\text{CCL}\_3\text{F}(\text{g}) \xrightarrow{\text{UV radiation}} \text{CCl}\_2\text{F}\left(\text{g}\right) + \text{Cl}\_{(\text{g})}$$

Ozone layer is destroyed particularly by these single chlorine molecules.

$$\text{Cl}\,(\text{g}) + \text{O}\_3(\text{g}) \rightarrow \text{ClO} + \text{O}\_2(\text{g})$$

Considerable amount of oxygen atoms are present in the stratosphere, because it produces oxygen atoms regularly by go through photo chemical breakdown. This will lead to the renewal of chlorine atoms in the stratosphere. So a lone CFC molecule can dismiss many ozone molecules.

$$\text{ClO}\,\,(\text{g}) + \text{O} \to \text{O}\_2 + \text{Cl}\,\,(\text{g})$$
