Question

Which atmospheric gas is primarily responsible for filtering sunlight in the \(120-220-\mathrm{nm}\) region? Which, if any, gas absorbs most of the Sun's rays in the \(220-320 \cdot \mathrm{nm}\) region? Which absorbs primarily in the \(320-400-\mathrm{nm}\) region?

Short answer

Oxygen absorbs in the 120-220 nm range, ozone in the 220-320 nm range, and minimally in the 320-400 nm range.

Step-by-step solution

Understanding the Spectrum

First, we need to identify the type of radiation in each specified range. The three ranges given are the ultraviolet part of the spectrum, which is divided into UV-C (100-280 nm), UV-B (280-320 nm), and UV-A (320-400 nm). The task involves identifying which gases absorb these different types of UV radiation.

Identifying the Gas for 120-220 nm

In the 120-220 nm range, which falls within the UV-C region, molecular oxygen (oxygen_2 ight) is primarily responsible for absorbing sunlight. This absorption leads to the photodissociation of oxygen molecules, which is an important process for creating ozone in the Earth's atmosphere.

Identifying the Gas for 220-320 nm

The 220-320 nm range covers part of the UV-C and most of the UV-B region. Ozone (ozone_3 ight) is the primary gas that absorbs most of the Sun's rays in this region. The ozone layer is crucial for protecting living organisms by reducing the amount of harmful UV-B radiation reaching the surface.

Identifying the Gas for 320-400 nm

In the 320-400 nm range, which is the UV-A region, ozone (ozone_3 ight) also plays a role in absorbing sunlight, but to a much lesser extent than in the UV-B range. Most UV-A radiation is not absorbed by the atmosphere and reaches the Earth's surface, where it can cause skin aging and DNA damage.

Key concepts

UV-C absorption

The UV-C radiation part of the ultraviolet spectrum spans from 100 nm to 280 nm. This type of radiation is critical because it has higher energy compared to UV-B and UV-A.
UV-C absorption plays a significant role in protecting life on Earth from the Sun's harmful ultraviolet emissions.One of the most crucial processes in this range is the interaction between UV-C and molecular oxygen (\( \text{O}_2 \)). When UV-C light hits oxygen molecules, it absorbs the energy, leading to a process called photodissociation.

• This absorption breaks down the oxygen molecules into individual oxygen atoms.
• The free oxygen atoms can then interact with other oxygen molecules to form ozone (\( \text{O}_3 \)), which is essential for our atmosphere.

Therefore, molecular oxygen acts as a primary shield against UV-C by filtering out a significant amount of this high-energy radiation.

ozone layer

The ozone layer is a significant part of our planet's atmosphere found primarily in the stratosphere. It acts as a protective shield by absorbing the majority of the Sun's harmful ultraviolet radiation and helps maintain the balance, which is vital for ecosystems.Ozone (\( \text{O}_3 \)) is most effective in absorbing UV-B radiation, which spans from 280 to 320 nm.

• In this region, ozone absorbs a large portion of UV-B radiation, preventing it from reaching the Earth's surface.
• By filtering out UV-B rays, the ozone layer prevents numerous biological hazards such as skin cancer, cataracts, and harm to plant life.

Although it absorbs some UV-A radiation (320-400 nm), the absorption is less prevalent. Hence, UV-A can reach the surface more easily, though the impacts here like skin aging are less severe compared to UV-B.The health of the ozone layer is a global concern, as any depletion would lead to increased UV radiation reaching the Earth's surface, with significant impacts on living organisms.

photodissociation of oxygen

Photodissociation is a process where photons, particularly those in the UV-C range, have enough energy to break apart molecules. Understanding photodissociation of oxygen is key to grasping how our atmosphere protects us.When UV-C radiation is absorbed by molecular oxygen (\( \text{O}_2 \)), it breaks the chemical bonds between the oxygen atoms, splitting the molecule into two separate oxygen atoms.Here is how it leads to ozone formation:

• Each free oxygen atom (\( \text{O} \)) can then combine with another \( \text{O}_2 \) molecule to form ozone (\( \text{O}_3 \)), which is a critical component of the ozone layer.
• The creation of ozone through photodissociation ensures there is sufficient ozone to absorb UV-B and part of UV-A radiation.

This process is essential in maintaining the protective nature of the ozone layer, and by regulating this composition, photodissociation contributes substantially to the shielding effect of our atmosphere against the Sun's ultraviolet rays.