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UV and IR

When looking at the spectrum of visible light, you can see that the final shade is a violet colour towards the left of the spectrum, whereas, towards the right, the last shade is red. This is where ultraviolet (UV) and infrared (IR) get their names. The visible light spectrum is just a small subsection of the electromagnetic radiation spectrum, and the wavelengths for UV and IR radiation are on either side. Today we shall be looking at some of the properties of UV and IR radiation, their differences, and their effects on our planet.

IR and UV Radiation

Understanding infrared (IR) and ultraviolet (UV) radiation are essential in environmental science because these two consequential types of radiation have significant effects on the state of our planet and its atmosphere.

Visible light is the range of electromagnetic (EM) radiation from 380 nanometres (nm) to 760 nanometres (nm).

The electromagnetic radiation spectrum can be depicted as various types of transverse waves. Infrared radiation ranges from 760 nm to about 14,000 nm, and ultraviolet radiation ranges from 380 nm to 200 nm.

Wavelength is the distance between each distinguishable crest of an electromagnetic or sound wave.

Transverse waves (such as electromagnetic waves) act in two dimensions meaning they can travel in multiple directions.

On the other hand, longitudinal waves are one-dimensional and only work in one direction.

UV and IR Spectroscopy Difference

Let's have a look at UV and IR spectroscopy radiations and compare their differences in more detail below.

Ultraviolet Radiation

UV radiation concerns the section of the electromagnetic spectrum ranging from X-rays to the violet end of visible light. Ultraviolet radiation is not visible to us humans, but when fluorescent materials absorb UV radiation, they will become excited. The sun's scorching surface emits UV radiation that reaches the Earth's atmosphere.

Too much UV radiation can be hazardous to humans (it can cause cancer and eye defects), so protection is vital, especially during long periods of exposure. Humans can wear sunscreen to protect their skin from UV.

The Earth's atmosphere has its own UV protection: the ozone layer.

We use ultraviolet radiation to kill bacteria and fluorescent light bulbs.

The ultraviolet radiation part of the EM spectrum is split up into three layers:

  1. UVA radiation (black light) is between 315-380 nm.
  2. UVB radiation is between 280-315 nm.
  3. UVC radiation is 280-100 nm.

Short-wavelength UV radiation is absorbed by oxygen in the atmosphere. As oxygen is abundant (for this purpose), UVC radiation does not reach the Earth's surface.

The Ozone Layer

The ozone layer is a subsection of the stratosphere with the most significant molecule of ozone (O3) concentration. Ozone is formed from oxygen molecules being split up by short-wavelength ultraviolet radiation from the sun. This produces an oxygen atom and an oxygen free radical, reacting with an alternative oxygen molecule and forming ozone. These ozone molecules are broken up by long-wavelength UV radiation forming oxygen molecules and an oxygen free radical, which reforms ozone elsewhere. Therefore, oxygen and ozone work together to protect the planet from harmful ultraviolet radiation.

A free radical is a highly reactive molecule that possesses a free electron.

Free radicals are very dangerous in the ozone layer and inside the body. Luckily, because of our diets, we have these amazing things called antioxidants (such as vitamins C and E) that work tirelessly to rid our bodies of dangerous free radicals. Antioxidants will neutralise free radicals by providing them with an electron to pair up with their reactive spare electron.

Infrared Radiation

Infrared radiation concerns the part of the electromagnetic spectrum between the red end of visible light and microwaves. Infrared radiation is also emitted from scorching surfaces like the sun. Absorption of infrared radiation produces a warming effect on a surface, and in the case of the sea, it can penetrate 100s of metres down, but with little warming effects in the depths of the oceans.

Thermal stratification is the formation of descending layers of a water body of lowering temperatures as the sun's rays fail to penetrate the depths.

Insolation is the amount of solar radiation reaching a given area at any time.

There are three sections of the infrared radiation spectrum too:

  1. Short-wavelength IR ranging from 780-2500 nm
  2. Medium-wavelength IR ranging from 2500-5000 nm
  3. Long-wavelength IR ranging from 5000-14000 nm

The shorter the wavelength, the higher the frequency of energy-carrying waves meaning more energy is transmitted.

Humans utilise infrared radiation in heating and drying products.

Effects of IR and UV on the Planet

Infrared, ultraviolet, and harmful forms of radiation, so when more radiation reaches the planet, damage is done to humans, ecosystems, and the climate. Let's first look at what affects the amount of radiation reaching the Earth's surface.

The Effects of IR Radiation: Greenhouse Gases

The effects of infrared radiation from the sun are essential in warming our planet and maintaining a temperate environment so life can survive. However, greenhouse gas emissions from human activity are causing the amount of IR radiation absorbed by the Earth's surface to increase. Greenhouse gases absorb IR radiation and re-emit it in all directions. So, when IR is reflected or re-emitted from the Earth's surface, instead of travelling back into space, some radiation is absorbed by greenhouse gases and re-emitted towards Earth's surface.

This is causing further warming and the climate crisis that we face today.

The Effects of UV Radiation: Ozone Depletion

The ozone layer is vital in protecting our planet from dangerous ultraviolet radiation effects. However, gaseous emissions from industrial activity in the 1900s are resulting in ozone layer depletion. Harmful molecules such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are split up into dangerous chlorine free radicals. These free radicals react with ozone molecules, forming oxygen molecules and other free radicals (like chlorine monoxide). This will reduce the ability of the ozone layer to absorb UV radiation, and more will reach the Earth's surface.

Increased IR Radiation

An increase in the amount of IR radiation reaching the Earth's surface will cause the warming of the Earth's system. This warming has a variety of negative impacts, such as:

  • melting ice caps,

  • rising sea levels,

  • droughts,

  • forest fires,

  • increased precipitation,

  • and increasingly frequent severe weather.

All these impacts will cause habitat fragmentation and mass species migrations that pressure ecosystems to adapt. Rising global temperatures will also cause agricultural methods to become more expensive, and less-developed countries in hotter climates to struggle with water shortages.

Many positive feedback mechanisms are associated with increased IR radiation.

Do not be fooled; they are not positive!

Melting ice sheets will decrease the reflective ability of the Earth while rising sea levels will engulf these sheets and cause more melting. Increasing temperatures will result in more evaporation too. This means that more water vapour will be present in the atmosphere. Water vapour is a potent greenhouse gas, so it will cause even more IR radiation to be re-emitted towards the Earth's surface.

Increased UV Radiation

Ultraviolet radiation transmits far more energy than IR and can directly harm humans and animals.

  • Overexposure to UV radiation has been shown to cause various forms of cancer in humans and eye defects such as cataracts.

  • Increased UV exposure affects the producer populations of ecosystems too. Less energy is available in high UV environments, so the developmental stages of photosynthetic organisms are elongated.

This will have ramifications for the entire ecosystem. This can be anything from dependent pollinators and herbivores to microorganisms that require the circulation of organic material to survive.

UV and IR - Key takeaways

  • Ultraviolet (UV) radiation is electromagnetic radiation between the violet part of visible light and X-rays on the EM spectrum. UV radiation has wavelengths between 100-380nm and is emitted from the sun's surface.

  • Infrared (IR) radiation is between the red part of visible light and microwaves on the EM spectrum. It has a wavelength between 760nm-14000nm and is also emitted from the sun's surface.

  • The ozone layer is essential in protecting our planet from UV radiation. Oxygen absorbs short-wavelength UV, while ozone absorbs long-wavelength UV.

  • Increasing exposure to IR radiation because of greenhouse gas emissions results in global warming and climate change. Climatic changes include rising sea levels, melting ice sheets, increased precipitation, and forest fires.

  • Overexposure to UV radiation can cause cancer and eye defects in humans and stunt growth in producer populations.

Frequently Asked Questions about UV and IR

UV has a shorter wavelength than IR and so is more dangerous to humans.

Both UV and IR radiation are emitted from the sun's surface.

Wavelengths of 760nm to 14000nm.

Overexposure to UV radiation causes cancer and eye defects in humans and affects producer populations in ecosystems.

Increased IR radiation warms the Earth's system and has negative impacts such as melting ice caps, rising sea levels, droughts, and increased precipitation.

Final UV and IR Quiz

Question

What is insolation?

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Answer

The amount of solar radiation reaching a surface.

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Question

What is wavelength?

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Answer

The distance between each crest of a wave.

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Question

What is the wavelength range of visible light?

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Answer

380nm-760nm.

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Question

What is thermal stratification?

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Answer

The formation of descending layers of lowering temperatures in water as the sun's rays fail to penetrate the depths.

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Question

How is ultraviolet radiation dangerous to humans?

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Answer

It causes cancer and eye defects.

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Question

How is ultraviolet radiation dangerous to producers?

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Answer

It can cause their developmental stages to take longer.

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Question

What is the effect of absorbing infrared radiation?

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Answer

Heating.

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Question

Which molecules deplete the ozone layer?

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Answer

Free radicals.

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Question

What substances form dangerous chlorine radicals in ultraviolet radiation?

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Answer

CFCs and HCFCs.

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Question

What type of ultraviolet radiation does oxygen absorb?

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Answer

Short wavelength ultraviolet radiation.

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Question

How are humans causing more infrared radiation to reach the Earth?

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Answer

Because we release greenhouse gases into the atmosphere, which absorb reflected IR and re-emit it back towards the Earth.

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Question

What are the consequences of increasing global temperatures?

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Answer

Rising sea levels, melting ice sheets, droughts, increased precipitation.

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Question

What is the positive feedback mechanisms involving ice?

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Answer

The more ice that melts, the less reflective power the Earth has to reflect IR back into space.

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Question

What is a free radical?

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Answer

A molecule or atom with a free electron.

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Question

What is the difference between transverse and longitudinal waves?

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Answer

Transverse waves are two-dimensional whereas longitudinal waves are one-dimensional.

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