**5.2 Photochemistry of ozone and Chapman's cycle for ozone loss**

Ozone was first discovered by a German chemist, Christian Friedrich in the year 1939. Ozone present in the stratosphere is formed by the chemical reactions between oxygen and sunlight. The production of stratospheric ozone is because of the chemical reaction balance.

One ozone molecule is broken into one oxygen molecule and the remaining oxygen molecule is absorbed by the ultra violet radiation [5]. The photochemistry of ozone depends on the interaction of sun's radiation with the in atmospheric gases, particularly with oxygen.

A clear understanding of ozone layer was first assumed by Chapman in the year 1930. According to Chapman, when oxygen is hit by high energy photon, it is fragmented into two oxygen atoms. The below equation depicts Chapman's reaction.

$$\mathbf{O}\_2 + \frac{\mathbf{h}\mathbf{c}}{\lambda} = \mathbf{O} + \mathbf{O}$$

Where h = plank's constant.

C = Speed of light (wavelengths shorter than 242 nano meters)

$$\lambda = \text{wavelength of photon}$$

Ozone production by solar ultra violet radiation produce more amounts of ozone than the actual amount of ozone present in the atmosphere. The production of ozone is balanced by ozone loss.

$$\text{O3} + \text{O} \rightarrow \text{O2} + \text{O2}$$

#### **5.3 Effects of ozone layer weakening**

#### **5.4 Effects on human health**

UVB causes nonmelanoma skin cancer and plays a major role in malignant melanoma development and it is evident by many Laboratory and epidemiological studies. Also, UVB causes eye cataracts. In general, sunlight contains some UVB, even with normal ozone levels. And it is advisable that there should be always a limit to the exposure to sun.

#### **5.5 Effects on plants and marine creatures**

Even a small amount of UV B radiation present in the sunlight will cause an impact in the physiological and evolving processes of plants. Damages to early developmental stages of fish, shrimp, crab, amphibians and other animals are caused by UV B rays. Some of the most severe effects of UV B radiation exposure to plants and animals are decrease in their reproduction capacity and reduced larval development. Even a small increase in UV (B) exposure could result in significant reduction in the size of the population of animals that eat these minor creatures.

#### **5.6 Hydrocarbons as refrigerants**

CFC -12 is having high ODP and very high GWP. Promising substitutes for CFC-12 are hydro carbons which do not have any halogen compounds. The satisfactory characteristics of hydrocarbons are environmentally safe, energy efficient, technologically reliable refrigerants. Hydrocarbons arise naturally formed from solidified plant matter, and throughout the world initiate as oil and natural gas. Flammability is the characteristic feature of HC type refrigerants and it is the concerning point to be considered as a refrigerant in air conditioning and refrigeration systems, even though it exhibits very low GWP values [6].

Lower paraffin's such as propane, butane, and isobutene were successfully used as refrigerant before the arrival of CFCs. The thermodynamic properties of the hydrocarbons are much better than any of the other alternatives to CFC's. Hydrocarbons are available at low price all over the world and are compatible with commonly used lubricants and materials of construction used in refrigeration systems. Hydrocarbons are very economical and they are readily available in most parts of the world.

### **6. Phase change materials as refrigerants**

Using phase change materials in air conditioning systems can be an effective method for improving the process of cooling as well as minimizing the size of the system. The nature of phase change materials is they will absorb, store and release large amount of heat. Generally, the temperature of PCM increases with the increase in the ambient temperature. Researchers conducted various studies in using phase change materials for the use in air conditioning systems. Co2 emission and power consumption of the systems using phase change materials are better in comparison with the conventional systems [7]. Around 7% of electrical power consumption reduction was observed in the air conditioner designed by Nataohorn Chaiyat and Tanongkiat Kiatsiriroat with PCM bed in comparison with the normal air conditioner [8]. During the transition period, the PCM melts and so absorbs heat. A reverse process happens when the PCM temperature is decreased [7]. Thermodynamic properties of CFC and Hydrocarbons are mentioned in the below **Table 4**.

#### **6.1 Applications of PCM**

1.**PCM used in wall systems:** PCM's have been successfully used in the middle layer of the wall systems and it is evident from many studies. PCM embedded in the wall systems can reduce the indoor air temperature up to 4.2°C [9].

*Refrigerant Mixtures DOI: http://dx.doi.org/10.5772/intechopen.99024*


#### **Table 4.**

*Thermodynamic properties of CFC and hydro carbons.*

