Ozone depletion: causes and effects
The ozone layer protects the earth from excessive irradiation of ultraviolet (UV) light. Influenced by the emission of
substances such as chlorofluorocarbons (CFCs) and halons has decreased the thickness of the ozone layer since 1980. The
resulting increased UV radiation has harmful effects on humans and nature.
The ozone layer
The stratosphere is the layer of air between about 15 to 40 km altitude. This naturally has a high concentration of ozone
and is therefore also called the ozone layer. Ozone protects the earth from excessive irradiation of ultraviolet (UV)
light from the sun. When talking about a decrease in the thickness of the ozone layer (or over the hole in the ozone
layer), then becomes a (strong) the reduction of the ozone concentration referred to in the stratosphere.
Above the Antarctic is the decrease of the ozone concentration much stronger than average on earth. This happens
especially during the spring season there. This has to do with the extremely low temperatures which prevail there in the
stratosphere in the winter, in combination with the presence of ozone-depleting substances (chlorine and bromine
compounds). This low temperature leads to the formation of polar stratospheric clouds (PSCs). On the surface of the cloud
droplets reactions occur with the chlorine and bromine compounds which ozone can be accelerated aborted when sunlight
returns in spring. Even in the Arctic occurs in this process, but to a lesser extent than in the Antarctic. The gap in
the ozone layer is therefore particularly in the Antarctic large. The gap varies greatly in size during a year and is
maximum in the spring season (September to November) there.
The thickness of the ozone layer over the last years not continue down
From about 1980 has decreased the thickness of the ozone layer, especially during the eighties and early nineties of the
last century. The reduction amounts to about 3% compared to the period before 1980. Around the mid-latitudes (35-60) is
the decrease about 3.5% in the northern hemisphere and about 6% in the southern hemisphere .
The decrease has not put further in recent years, and stabilizes so now more-or-more on this lower level. This is due to
the fact that the peak in the concentrations of substances that deplete the ozone layer is reached. This is because the
global production and use of ozone-depleting materiales under the influence of the internationally agreed Montreal
Protocol was strongly reduced. The concentrations of the major ozone-depleting substances are therefore declining.
By further decline may occur in time recovery of the ozone layer. The ozone hole over the Antarctic will persist for many
decades. A full recovery of the ozone layer will take more than 50 years.
UV radiation increases
The thinning of the ozone layer results in an increase of the UV radiation on the earth's surface. In the Netherlands, the
total skin cancer relevant UV radiation since 1980 increased by about 10%.
Effects of the increase in UV-load
An increase in UV radiation causes numerous adverse effects on health and the environment, including additional cases of
skin cancer. Based on the average UV irradiation in the period 2004-2006, in time the annual number of people with skin
cancer in the Netherlands increased by 150-200 per million inhabitants. In total there will be over 2400 additional cases
compared to 1980. Of these extra cases per year is estimated about 40 people died. As the ozone layer recovers, will be in
the Netherlands the additional number of annual cases of skin cancer from ozone depletion around the middle of the 21st
century come in at around 1500 per year.
0 comments: