The Ozone Layer.

The Ozone Layer

Introduction

Since the mid 1980's scientists have been aware of the continuing depletion occurring in the ozone layer. First discovered over the South Pole, these holes are thought to be the cause of excessive use of chlorofluorocarbons (CFC's, found in aerosols and refrigerators) and emissions from the petrochemical industry.

Ozone (Oз) itself is a highly reactive and unstable form of oxygen found in the stratosphere, but, while poisonous to humans if inhaled, it is also our natural defence against UV radiation.

As people become more aware of this worsening problem and the effects of UV on the skin the demand for more effective chemical sunscreens has intensified - enter the chemists.

Aim

The aim of my investigation is to try different sun blocks of the same brand (differing factors) to test their UV blocking properties and attempt to identify the active ingredients used. I'll also test some household products for their UV blocking effectiveness. My results should then help me answer the question, "what makes a good sunscreen?".

Research

Ultraviolet Light…

(1) UV radiation reaches the earth's surface in two types:

UVa - wavelength between 320 - 400nm

UVb - wavelengths between 280 - 320nm

UVc is wavelength 200 - 280nm, however, this doesn't reach the earth's surface as the stratosphere absorbs it.

The Effect Of Light On The Skin…

The above diagram shows how the effects of light on the skin varies with increasing frequency, the higher the frequency, the more damage caused.

Prolonged exposure to ultraviolet light can cause cataracts, premature skin ageing, sunburn and (at the right frequency) it can break up the DNA in our cells, causing mutations and leading to skin cancers.

SPF: This is known as the Sun Protection Factor and is a measure of the protection supplied by a sunscreen. The factor is the number of times that a sunscreen reduces the effect of the sun on your skin, so SPF15 reduces exposure to 1/15 of normal (2).

What Happens When Light Interacts With Matter?

UV can, of course, pass energy onto other materials, increasing their energy and creating a number of possible responses. Of these responses, the ones most relevant to my investigation are…

Excitement - When electrons become excited from absorbing a certain frequency of UV

Photodisassociation - where an electron absorbs so much light that the atom is belongs to no longer functions properly, causing molecules to break apart

Ionisation - when energy absorbed from a very high-energy photon causes an atom to completely lose an electron

If a molecule achieves photodisassociation (or ionisation) then the light energies being absorbed correspond to ...