Zoology · Ch 13 — Environmental Issues
Ozone Depletion
Ozone Depletion
At roughly 15 to 30 kilometres above ground level, Earth's atmosphere carries a thin layer of ozone that absorbs ultraviolet sunlight; this layer sits within the atmospheric zone called the stratosphere and acts as a protective covering against solar UV radiation. The ozone molecule (O3) consists of three oxygen atoms and forms when atmospheric oxygen (O2) exposed to solar radiation splits into two separate oxygen atoms, each of which then joins a single oxygen atom to form ozone. The ozone molecule itself is unstable and soon decays back into molecular oxygen, so this formation-and-decay cycle runs continuously in the upper stratosphere under normal conditions.
Ozone layer depletion occurs mainly through anthropogenic (human-caused) actions: the excessive release of chlorine and bromine from man-made compounds -- chlorofluorocarbons (CFCs), methyl chloroform, carbon tetrachloride, hydrochlorofluorocarbons, hydrobromofluorocarbons, and methyl bromide -- has a direct, documented impact on ozone-layer depletion, and these compounds are collectively categorised as ozone-depleting substances (ODS).
The effects of this depletion follow directly from the ozone layer's protective role: with less ozone to absorb it, more UV radiation penetrates deep into the skin, causing premature skin ageing and wrinkling, suppression of the immune system, skin cancer (melanoma), and chronic eye damage; the free radicals and reactive oxygen species this radiation generates can also damage DNA directly. Depletion is concentrated seasonally over the polar regions -- the well-known 'ozone hole' over Antarctica develops each year between late August and early October, visible on satellite maps as a distinct region of markedly thinner ozone measured in Dobson units. …
What this figure shows. A false-colour satellite map, credited to NASA, titled 'Ozone depletion around Polar region', showing the ozone hole over Antarctica as a distinct purple-shaded region against the surrounding atmosphere. A colour scale running from violet through to red represents ozone thickness measured in Dobson units, with violet/purple marking the lowest ozone thickness (the thinnest part of the layer, i.e., the hole itself) and progressively warmer colours marking thicker, less depleted ozone further from the pole. The map illustrates the text's point that the Antarctic ozone hole is not a permanent fixture but a seasonal phenomenon that develops each year between late August and early October, when specific atmospheric and temperature conditio …