Question

In the abstract of a talk he gave in 2007 , Nobel laureate W. Sherwood Rowland wrote "Solar UV radiation creates an ozone layer in the atmosphere which in turn completely absorbs the most energetic fraction of this radiation." a. What is the most energetic fraction? b. How does solar UV radiation "create an ozone layer"?

Short answer

a. The most energetic fraction is UVC radiation. b. Solar UV radiation creates the ozone layer by splitting O_2 molecules into atomic oxygen, which then forms ozone.

Step-by-step solution

Understanding UV Radiation

Solar UltraViolet (UV) radiation is divided into three types based on their wavelengths: UVA (320-400 nm), UVB (290-320 nm), and UVC (100-290 nm). UVC is the most energetic fraction since it has the shortest wavelength and thus the highest energy.

Exploring Ozone Layer Formation

The creation of the ozone layer involves the photodissociation of molecular oxygen. When high-energy UVC radiation reaches the atmosphere, it splits molecular oxygen ( O_2) into individual oxygen atoms ( O). These atoms can then bond with other O_2 molecules to form ozone (O_3). This process is known as the ozone-oxygen cycle.

Key concepts

Understanding UV Radiation

Solar UltraViolet (UV) radiation is a type of energy emitted by the sun. It is divided into three categories based on their wavelengths: UVA, UVB, and UVC. Understanding the differences between these types is crucial. UVA ranges from 320 to 400 nanometers and is the least energetic, yet it penetrates the Earth’s atmosphere with ease. It plays a significant role in skin aging and wrinkling. UVB, with wavelengths from 290 to 320 nanometers, is more energetic than UVA and is known for causing sunburn. UVC covers wavelengths from 100 to 290 nanometers and is the most energetic. However, UVC mostly gets absorbed by the ozone layer before reaching the Earth's surface. The shorter the wavelength of the radiation, the higher the energy it carries, making UVC the most energetic type of UV radiation.

UVC and Its Impact

UVC radiation, due to its short wavelength, carries a lot of energy. This high energy allows UVC to split oxygen molecules in the atmosphere. UVC’s energy is strong enough to break the bonds of molecular oxygen (O_2), resulting in two separate oxygen atoms. This splitting process plays a vital role in forming and maintaining the ozone layer. Luckily, the Earth's ozone layer is highly effective at absorbing UVC radiation, preventing it from reaching the ground. This absorption not only shields life on Earth from the harmful effects of UVC but also enables the formation of ozone molecules. Without the absorption of UVC, the higher energy radiation could cause severe damage to living cells.

The Ozone-Oxygen Cycle

The ozone-oxygen cycle is a natural process that sustains the ozone layer in the Earth's atmosphere. It starts when UVC radiation splits oxygen molecules (O_2) into individual oxygen atoms. These free oxygen atoms then collide with other oxygen molecules to form ozone (O_3).

• This process helps form the protective ozone layer that absorbs significant portions of UV radiation.
• The ozone itself can also absorb UVB and UVC radiation, causing the ozone molecule to split again into an oxygen molecule and a free oxygen atom.
• This newly freed oxygen atom can recombine with another oxygen molecule, continuing the cycle.

Thus, the cycle keeps replenishing the ozone layer and plays a crucial role in protecting life on Earth. However, human activities have threatened this natural cycle, leading to concerns about ozone depletion.