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Clinuvel Photoprotection

UV & Light

3 levels of knowledge [general, professional, academic]

Introduction

The most important source of light and subsequent energy on earth is the sun. The sun emits energy that can be absorbed by organisms and molecules where it facilitates countless reactions, including photosynthesis, ozone production, vitamin D, and weather phenomena.

Ultraviolet radiation (UVR)

Sunburn and skin cancer are known to be correlated to the dose of UV radiation our skin encounters. UV radiation is emitted by the sun, and is a region in the electromagnetic spectrum between 400-200nm, that can be broken down into three categories: UVA which is between 400-320nm, UVB which is between 320-280nm, and UVC between 280-200nm. As the various types of UV radiation are at different wavelengths, they react differently with the atmosphere. Almost all of the UVC radiation, some of UVB and UVA is absorbed before it reaches the Earths surface. The dose of UVA, UVB and UVC changes as UV passes through the atmosphere mainly due to differences in rates of reflection, refraction, scattering and absorption. The change can be emulated on a UV index (Figure 1). A local UV index can be found in a variety of places reporting on meteorological data and forecasts (Clinuvel's YOUV device is one such example). UVI depicts how much UV radiation is likely to be reaching the Earth’s surface and therefore which precautions should be taken to minimize human risk.

A UV index value of zero corresponds to no UVR reaching the Earth’s surface, which occurs at night time, and an index of 10 refers to roughly midday sun, when there is no cloud cover. UVR indices record well into the teens when the ozone layer reads low values. The index numbers are measured in watts/meters2, and the measurements reflect different wavelengths to be more harmful than others.

Figure 1. UV index.

Figure 1. UV index. (Click image to expand)

Note that the above precautions are provided for adults with moderately fair to dark skin tone, and that skin damage caused by sun exposure is accumulative over one’s lifetime.

Ozone

As light enters the Earth’s atmosphere, it comes into contact with molecules in the stratosphere. The stratosphere is situated about 10km above sea level and continues up until 50km above sea level. It contains the ozone layer, which absorbs UV radiation. The ozone layer is composed of ozone, a molecule containing 3 oxygen atoms. Oxygen molecules are good absorbers of UVC radiation, using this energy the oxygen bonds break, forming two separate oxygen atoms. These atoms can rejoin, recreating the oxygen molecule, or binding to an oxygen molecule ultimately to form an ozone molecule. Ozone molecules are good absorbers of UVB, and to a lesser degree, UVA. Ozone molecules absorb the energy provided by UVB and UVA to undergo dissociation, releasing oxygen atoms that can combine to form oxygen molecules. These two reactions are in equilibrium, where neither really dominates. Ozone is an important molecule in reducing the amount of harmful UV radiation that passes through our atmosphere, but at low altitudes, such as on the surface of the Earth, it becomes a somewhat toxic and unstable molecule.

Figure 2. Production of ozone in the atmosphere.

Figure 2. Production of ozone in the atmosphere.

The amount of UV light that reaches the Earth's surface varies and is dependent on a number of factors:

  • Latitude: Near the equator, where the sun is directly overhead, the distance from the sun to the ground is the shortest, and the UV has to pass through the least amount of radiation. Therefore, on the equator, the UV intensity is the highest. Likewise, on the poles, the sun appears low in the sky, meaning the light has to pass though more radiation-absorbing atmosphere to reach the surface.
  • Elevation: At higher altitudes there is less atmosphere to absorb UV radiation, therefore individuals are exposed to a greater amount of UVR.
  • Proximity to an industrial area: photochemical smog produced in industrial processes contains artificially produced ozone. The ozone produced can absorb more UV radiation, but also poses significant health risks if it is low lying.
  • Weather conditions: cloud cover can reduce the UV levels on the surface, but often incompletely.
  • Reflection: some surfaces are able to reflect UV radiation, meaning there is a greater chance of getting sun burnt, even in shady places. Snow, sand, grass and water are good reflecting surfaces.
  • Time of day/year: during the middle of the day, the sun is at its highest position in the sky, resulting in the least distance for radiation to travel, and more exposure to UV light. The summer months also provide the most intense UV radiation, as the sun’s angle (zenith angle) is reduced.
  • Ozone layer: the depth of the ozone layer plays a vital role in reducing exposure to UV light. The ozone layer has been found to be thinning in the past few decades. This is presumably due to the release of ozone degrading chemicals by industry.

Ozone depletion

In the past few decades, it has been observed that the ozone layer is thinning over certain regions of the globe, particularly over Antarctica. This has been attributed to chemicals that have been released by industry since the 1930’s, particularly gaseous chlorine and bromine containing substances, such as chlorofluorocarbons (CFC’s) and bromofluorocarbons (BFC’s).

Ozone can be broken down by natural and manmade sources. Atomic chlorine and bromine are two significant contributors, and can be released into the atmosphere by large volcanic eruptions and are also present in chemicals, especially those that where used by industry decades ago, such as CFC’s and BFC’s. CFC’s have been produced as a substitute for toxic and flammable chemicals used in industry, such as ammonia. They’re non-toxic, non-flammable, and their very stable nature made them perfect for propellants in aerosol cans and refrigerants. Their use have grown exponentially (in 1988 it was estimated that over one billion kilograms were being produced annually worldwide) until the discovery that CFS had the capacity of thinning the ozone layer. At this stage world leaders acted by signing the Montreal Protocol, which stipulated that consuming and producing chemicals capable of breaking down ozone be phased out by 2000.

CFC and other similar chemicals are so stable that they’re not destroyed in the troposphere, as they slowly rise towards the stratosphere. These stratospheric molecules are found to be able to break ozone down into an oxygen atom and molecule. This usually occurs at a slow rate, reducing the overall thickness of the ozone layer by about 4% per decade, but in the atmosphere above Antarctica, especially in spring, thinning occurs at an alarming rate. During its winter, Antarctica becomes cold enough (-80°C) for stratospheric clouds (termed Stratospheric Clouds Mother of Pearl, PSCs) to form in the ozone layer. On the surface of these clouds, chlorine and bromine are transformed into an active state and when the sun gains intensity in the spring, clouds disappear freeing chlorine and bromine to rapidly destroy ozone. As temperatures further continue to warm, wind vortexes holding the particles above Antarctica break up, mostly allowing ozone rich air to flow into ‘the hole’. The chlorine and other molecules capable of breaking ozone down can destroy up to a thousand molecules of ozone before it is converted into an inactive form, such as hydrochloric acid.
There are many complex reactions that destroy ozone, the simplest being: a free chlorine atom reacts with an ozone molecule, forming a chlorine and oxygen complex, ClO and an oxygen molecule, O2. The ClO then reacts with a free oxygen atom forming an oxygen molecule and a free chlorine atom. In this manner a circular process is initiated.
Although the Montreal Protocol, first signed in late 1988, will help assist to reduce the effects of destructive radicals in the atmosphere, the effects will not be instantaneous. As it takes years for the CFC’s and other molecules to reach the stratosphere, the reduction in emissions will have minimal effect in the stratosphere (the largest dimension of the hole over Antarctica was measured in 2006, being over three times the size of Australia). It is anticipated that it will take a decade before confirmation of recovery of the ozone can be given.

With the thinning of the ozone layer, less UVB radiation is absorbed resulting in more harmful radiation passing to the Earth’s surface. This would result in increased incidence of skin cancer, cataracts, and other UV related diseases.

Definitions and focus

The energy in the light emitted by the sun and all other sources, travels as mass-less, charge-less particles, photons. Photons can travel as both particles and waves, where each beam of light has its own wavelength (measured peak to peak: Figure 3), frequency (number of wave cycles passing a point per second, Hertz) and energy.

Figure 3. A typical wavelength.
 
Figure 3. A typical wavelength.

The wavelengths of visible light range from 400nm to 700nm. Once the wavelength drops outside of these values a different form of electromagnetic radiation transpires; these different forms can be found on an electromagnetic spectrum (Figure 4). As evident on Figure 4, the two main sources of electromagnetic radiation emitted by the sun (visible light and ultraviolet radiation - UVR) only occupy a small section of the spectrum.

Figure 4. Electromagnetic spectrum.
 
Figure 4. Electromagnetic  spectrum.

Environment

The heat supplied by the sun has provided us with a suitable environment to survive. Once radiating energy is passed through the atmosphere, the photons collide with matter, transferring energy. This causes heat, wind, rain, clouds and other weather phenomena. Wind is a result of the varying temperatures of the air above land and water. The hot air rises, causing a flow of cooler air to occupy its previous place, and eventually cool air, high in the atmosphere, drops down to sea level, completing the cycle. When ocean water is heated, water particles evaporate into the air, where they culminate to form clouds. These clouds pushed over land by winds experience lower temperatures, causing condensation into droplets and precipitation. Differences in atmospheric moisture, pressure and temperature result in dramatic weather conditions as hurricanes, cyclones and tornadoes.

When the sun’s rays are shone on an organism, it can have harmful consequences. Different types of electromagnetic radiation have various effects on tissue and DNA. The ultraviolet region of the electromagnetic spectrum can cause serious damage to organic tissues, including human tissue. Humans are protected against ultraviolet radiation by various natural defense mechanisms. Ultraviolet radiation (UVR) can also cause damage to our eyes, both short and long term.

For instance the conjunctiva of the eye may show inflammatory reactions when exposed to intense UVR. Long-term eye (ophtalmis) exposure to sun may have deleterious effects on the retina, causing immediate, and sometimes permanent, visual loss. Long-term UV exposure contributes to cataract formation.

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