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Ultraviolet radiation (UVR) is the portion of solar
radiation with wavelengths of 200-400 nm (nanometers). Radiation of these short
wavelengths vibrates at very high frequency and is powerful enough to damage
living cells and tissues.
The most energetic UVR, UV-C (200-280 nannometers) is lethal, but nearly all is absorbed by ozone and oxygen in the atmosphere. Both UV-B (280-320 nm) and UV-A (320-400 nm) radiation reach earth’s surface and are damaging to living organisms.
Although nine percent of the sun’s radiation is UVR, much less reaches Earth’s surface, because ozone (O3) in the stratosphere strongly absorbs it. For that reason, the stratospheric ozone layer is often called the ‘ozone shield’. The thickness of the stratospheric ozone layer varies seasonally and latitudinally, owing to differences in the amount of sunlight in a region. Water vapor and aerosols also absorb UVR, so little of it reaches the sea surface or ground on very cloudy days or where air is polluted.
Man-made chemicals---particularly chloroflourocarbons (CFCs) used as refrigerants, fire suppressants, and propellants---have destroyed portions of the ozone shield during recent decades, allowing more UVR to reach Earth’s surface. These gases can be released into the atmosphere both deliberately or accidentally in the mistaken belief that they are inert. When UVR comes in contact with a CFC molecule, the cyclical reaction can repeatedly destroy ozone molecules.
Areas of ozone thinning occur over high latitude areas, principally in spring and summer. Ozone thinning is greatest over polar areas because seasonal circular air currents trap CFCs for months at a time and high altitude ice crystals accelerate their ability to deplete ozone.
A one percent decrease in overhead ozone allows one percent more UV-B light at 310 nm and three percent more at 305 nm to reach Earth’s surface.
UVR reaching earth's surface not only directly harms living tissue and materials such as paint or rubber, but it also reacts with chemicals in the air to produce ozone, which is so reactive that it harms or destroys both living (e.g. skin, lungs) and non-living (e.g. rubber, plastic, paint) materials.
How Was It Measured?
Data from two different satellites were used to obtain daily Local Noon Erythemal UV Irradiance (mW/m2) data: the Earth Probe/TOMS and Aura/OMI satellites (descriptions available here). UV Radiation was measured as the number of times in each 1-degree cell, that the monthly average exceeded the
climatological mean +1 standard deviation These values were summed across the 12 months to provide a single
value, ranging from 0-19. This was done separately for each satellite, since irradiance values were not perfectly synchronous between them.
All pressures have different affects on different goals. For each goal, the affect of each pressure is weighted 'low' (1), 'medium' (2) or 'high' (3). The actual data-derived value of the pressure is then multiplied by the weight assigned to it for that goal. That process is repeated for each pressure-goal combination. The sum of those values divided by 3 (the (the maximum pressure-goal value) expresses the total affect of that pressure on the goal.
UV Radiation has low effect (weight = 1) on Natural Products (Coral), Coastal Protection (Coral), and Biodiversity (Habitats-Cora, and Species).
What Are the Impacts?
UV-B damages the tissues of terrestrial plants, terrestrial
animals and marine organisms, including plant and animal plankton (Hader et al. 2003). While many plants,
including mangroves, sea grasses, salt marsh grasses, seaweeds and some
phytoplankton algae can protect themselves by manufacturing protective pigments
that function as “sunscreens,” UV-B can impair early larval developmental
stages of fish, shrimp, crabs, and other animals.
Tropical corals are exposed to high levels of UVR. They are restricted to warm, clear, relatively shallow water and high light intensity because much of their nutrition is provided by symbiotic photosynthetic algae (zooxanthellae). Corals produce chemicals that absorb UVR or act as anti-oxidants, as UVR can injure their skeletons, depress photosynthesis of zooxanthellae, harm coral larvae and contribute to ‘coral bleaching’.
Increased levels of UVR associated with stratospheric ozone depletion could overwhelm such natural defenses.
UVR increased mutation rates and negatively affected reproduction and development in attached seaweeds and in many species of phytoplankton algae (Häder et al. 2007). UVR was identified as the major factor causing algal zonation in the intertidal zone.
HUMAN HEALTH IMPACT
UV-B causes sunburn, induces skin cancers, degrades elastin
in the skin, causes cataracts in the lens of the eye, suppresses immune
response to Herpes simplex virus, slows healing of skin wounds and may
harm the spleen. Reduction of overhead ozone by one percent increases skin
reddening or sunburn by about one percent, but increases the incidence of skin
cancers by two to three percent (United Nations Environment Program 1994).
By the end of September 2011, the South Polar ozone hole reached Southern Argentina, Chile, and the Falkland Islands with stratospheric ozone concentrations decreased by 40%. Residents were warned to wear protective sunscreen, a hat and sunglasses with a UVR rating if they went outside during the peak hours of exposure.
UV light that penetrates through the stratosphere into the lower atmosphere also causes harm by reacting with oxides of nitrogen (NOx), carbon dioxide (CO2) and volatile organic compounds (VOC) emitted by factories, electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents to form ozone and smog. Smog levels could rise in coming years if emission from fossil fuel combustion remains high, because higher temperatures associated with climate warming accelerate the chemical reactions that form ground level ozone (Knowlton et al. 2011).
Nationwide ozone smog in 2002 exposed nearly 288 million Americans to pollution above the maximum health-based standard, which was then 80 ppb of ozone. It caused premature deaths of 795 people, hospitalization of 4,150 people and more than 365,000 outpatient visits.
Because ozone itself is so reactive, at ground level it harms human, animal and plant tissues and also damages materials such as paint and rubber.
Health costs related to ozone smog pollution can escalate
health-related costs for families, businesses and communities. Costs of the
2002 U.S. ozone event were $6.5 billion.
UV Radiation can negatively impact the tourism industry due to increased exposure and climate change.
Reductions in commercial fish populations due to UV-B exposure and climate change can impact potential annual revenues.
Some of the world’s most important food crops are particularly vulnerable to increased UVR, which reduces growth, photosynthesis and flowering in wheat, rice, barley, oats, corn, soybeans, peas, tomatoes, cucumbers, cauliflower, broccoli and carrots.
The costs of replacing plastic, rubber, paint and other materials degraded by UVR and ground level ozone are significant.
What Has Been Done?
The Montreal Protocol, first signed in 1987, is said to be the most successful international agreement in history, and perhaps the first truly global agreement. Most countries have
already phased out production of chloroflourocarbons (CFCs) and have replaced
them with hydrochlorofluorocarbons (HCFCs), which are less damaging to the
ozone shield. The next stage will be to eliminate HCFCs entirely and replace
them with hydrofluorocarbons (HFCs), which are thought to be non-damaging to
stratospheric ozone. On September 21,
2011, the United Nations held a Montreal Summit, at which 200 countries agreed
to eliminate hydrochlorofluorocarbons (HCFCs) by 2020 (developing nations were
given until 2030). Replacement of all refrigerants, fire suppressants and propellants by HFCs would eliminate UVR problems caused by the ozone hole, but it would increase global warming, because some HFCs trap heat up to a thousand times more effectively than does CO2. Negotiations are underway to modify the Montreal Protocol so that the most harmful HFCs can be regulated or phased out.
Get More Information
Environmental Health and Safety
EHSO provides information and resources pertaining to
the science of ozone
Fotobiologia Playa Union (EFPU)
A comprehensive list of scientific publications addressing
the effects of UVR on phytoplankton productivity and related topics.
The Ozone Hole
An organization dedicated to protecting the ozone layer by
raising public awareness on an international level.
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