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 \(220-320-\mathrm{nm}\) region? Which absorbs primarily in the \(320-400-\mathrm{nm}\) region?

Short answer

N₂ absorbs 120-220 nm, O₃ absorbs 220-320 nm, and O₃ partially absorbs 320-400 nm.

Step-by-step solution

Understanding the UV Regions

We need to identify gases responsible for absorbing sunlight in three different ultraviolet (UV) wavelength ranges: 120-220 nm, 220-320 nm, and 320-400 nm. Each of these UV regions interacts with different gases in the Earth's atmosphere.

Identifying the Gas for the 120-220 nm Region

The 120-220 nm region falls under the category of extreme ultraviolet (UV). Gases in this range are subjected to high-energy UV radiation. Molecular nitrogen (\(\text{N}_2\)) is the primary gas in the atmosphere that absorbs this high-energy UV radiation.

Identifying the Gas for the 220-320 nm Region

The 220-320 nm region corresponds to the UV-C range. In this region, ozone (\(\text{O}_3\)) plays a crucial role as it absorbs the majority of these UV rays, protecting living organisms from their harmful effects.

Identifying the Gas for the 320-400 nm Region

The 320-400 nm range is known as the UV-B and UV-A range. While the ozone layer does absorb some of the UV-B radiation, most of the UV-A radiation in the 320-400 nm band passes through the atmosphere. Thus, ozone (\(\text{O}_3\)) is less effective in this region, and there is no additional gas that absorbs primarily in the 320-400 nm range.

Key concepts

Ultraviolet Radiation

Ultraviolet (UV) radiation is a part of the electromagnetic spectrum emitted by the sun. The UV spectrum is classified into three main categories based on wavelength: UV-A, UV-B, and UV-C. Each category has distinct properties and interactions with the Earth's atmosphere. - **UV-A (320-400 nm):** This wavelength has the longest UV rays, penetrating deep into the atmosphere. It can reach the Earth's surface, affecting skin and eyes without being significantly absorbed by atmospheric gases. Ozone provides some protection from UV-A, but it's limited. - **UV-B (280-320 nm):** These rays are more energetic and can cause more harm, such as skin burns and eye damage. The ozone layer absorbs most UV-B radiation, acting as a crucial shield for ecosystems and human health. - **UV-C (100-280 nm):** This range contains the highest energy UV radiation. It's entirely absorbed by the atmosphere before reaching the surface. Primarily absorbed by ozone and molecular nitrogen, it presents a natural protection against these harmful rays. Understanding UV radiation helps explain how atmospheric gases filter sunlight and protect life on Earth.

Molecular Nitrogen Absorption

Molecular nitrogen ( N_2 ) is the most abundant gas in Earth's atmosphere, making up about 78% of it. While it's inert and nonreactive at ground level, in the upper atmosphere, it plays a vital role in absorbing extreme UV radiation. Molecular nitrogen is particularly effective in absorbing UV-C radiation within the 120-220 nm range. This capability helps block dangerous high-energy radiation from penetrating deeper into the atmosphere. By doing so, it contributes significantly to maintaining the balance of life by protecting organisms from potential DNA damage caused by extreme ultraviolet exposure. This absorption capacity is crucial for safeguarding the ozone layer and preventing additional UV radiation from reaching the Earth's surface, ensuring a stable environment for all living beings.

Atmospheric Gases

The Earth's atmosphere is a complex mixture of gases, each playing different roles in absorbing solar radiation. While made predominantly of nitrogen and oxygen, smaller amounts of other gases like ozone ( O_3 ) play significant, specialized roles. - **Ozone ( O_3 ):** This plays a pivotal role in absorbing the majority of UV-B radiation (220-320 nm), forming a protective layer in the stratosphere known as the ozone layer. It also absorbs some UV-A, although it is less effective in the 320-400 nm range. - **Molecular Oxygen ( O_2 ):** Absorbs UV light below the 200 nm range, providing initial protection before ozone takes over in the higher bands. These gases assist in creating a natural shield by filtering and absorbing the sun's UV radiation, thus maintaining a suitable environment for life. Without these gases, especially ozone, the increase in harmful UV-B and UV-C radiation would cause more severe biological effects, compromising ecosystems worldwide.