Which absorb ultraviolet radiation

This in contrast to ozone in the troposphere, the lowest layer of the atmosphere, where it is an air pollutant and can be harmful to humans, animals and vegetation. Over the last few decades, emissions of human-made chemicals have impacted the amount of ozone in the atmosphere. On 1 January , the Montreal Protocol on Substances that Deplete the Ozone Layer a protocol to the Vienna Convention for the Protection of the Ozone Layer entered into force as an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion.

As a result of this first universally ratified treaty in United Nations history the ozone layer is slowly recovering. To ensure the treaty is successfully executed over this long time period, policy makers need information about the amounts of ozone and related chemical species in the stratosphere.

CAMS monitors the ozone layer on a daily basis showing, for instance, the extent and magnitude of the ozone hole each year as it develops and recovers. Photokeratitis is a painful condition caused by the inflammation of the cornea of the eye. The eye waters and vision is blurred. Conjunctivitis is the inflammation of the conjunctiva the membrane that covers the inside of the eyelids and the sclera, the white part of the eyeball ; see Figure 3 which becomes swollen and produces a watery discharge.

It causes discomfort rather than pain and does not usually affect vision. Examples of eye disorders resulting from UV exposure include "flash burn", "ground-glass eye ball", "welder's flash" and "snow blindness" - depending on the source of the UV light causing the injury.

The symptoms are pain, discomfort similar to the feeling of sand in the eye and an aversion to bright light. Maximum absorption by the cornea occurs around nm. Absorption of UV-A in the lens may be a factor in producing cataract a clouding of the lens in the eye. A variety of instruments are commercially available for measuring UV radiation in the laboratory and in the workplace. Specifications and purchasing information can be obtained from suppliers of workplace monitoring equipment.

There are no Canadian regulatory occupational exposure limits for UV radiation. These limits are given below:. For the UV-A or near ultraviolet spectral region to nm , exposure to the eye should not exceed 1 milliwatt per square centimeter 1.

For exposure times less than seconds, the dose total energy should not exceed 1. Additional exposure limits apply to the amount of UV light exposure to the skin and the eyes. The amount of UV exposure a person can receive on their skin or eyes during an 8-hour period varies with the wavelength of the UV radiation. UV radiation is invisible and therefore does not stimulate the natural defenses of the eyes.

Workers must use eye and skin protection while working with UV radiation sources which present the potential of eye harmful exposure. The selection of eye protection depends on the type and intensity of the UV source.

UV radiation is easily absorbed in a variety of materials. Shielding is usually easy to design. Mercury lamps and metal halide lamps have an outer glass cover to stop UV radiation, and are designed such that if the outer glass is broken, the lamp ceases to function.

Certain industrial chemical pollutants in the atmosphere are gradually eroding earth's protective shield ozone layer which stops the sun's UV radiation from reaching the earth. In recent years, there has been growing concern about increasing levels of UV radiation in the sunlight, especially during the summer months. Excessive exposure to ultraviolet rays can cause skin cancer and eye cataracts.

Ways to limit exposure to the sun's UV radiation include avoiding working in the sun, wearing protective clothing and hats, and applying sunscreens. Protective clothing can include long pants, hats, and long-sleeved shirts.

Some newer, sun-resistant fabrics are more efficient in blocking UV radiation. Physical sunscreens e. Chemical sunscreens are non-opaque i. Broad spectrum sunscreens are intended to block both types of UV radiation.

Sunscreens are rated according to Sun Protection Factor SPF , an index of protection against skin erythema reddening of the skin. The higher the SPF is, the more protection it offers. For example, sunscreens should be applied 20 minutes before going outdoors, and reapplied every two hours, or more often if perspiring sweating , swimming, or working in water.

Use a broad spectrum lip balm with an SPF of 30 or higher as well. We hear on the radio and read in the newspapers about the UV index as a part of the weather forecast.

The UV index is a measure of the intensity of UV radiation in the sunlight that causes reddening of the skin erythema. The UV index can increase the mid-teens at midday in the tropics.

The implications of the UV index are summarized in Table 3. Besides direct sunlight, UV radiation exposure can occur via indirect routes. The following factors must be remembered in this regard:. In the oceans, lakes and rivers UV-B has adverse effects on many different aspects of the biology of organisms across the food web. Through these effects on ecosystems, large-scale increases in UV-B could alter the exchange of carbon dioxide between the atmosphere and the biosphere. Increased UV radiation also stimulates the breakdown of decaying leaves and other organic matter.

Together, the effects of increased UV-B would reduce the ability of ecosystems to trap carbon dioxide, including carbon dioxide produced by human activities.

In this way, large-scale ozone depletion would have worsened the build-up of carbon dioxide in the atmosphere that is causing climate change. Changing UV-B also alters the cycling of nitrogen and other chemicals in the environment, which may worsen air pollution. Exposure to UV-B also damages natural and synthetic materials.

Vulnerable materials include wood, plastic, rubber and even the materials used in some solar panels. These materials, widely used in buildings, agriculture and commercial products, are already designed to minimize the damage caused by UV. This would have led to more rapid deterioration and the need for additional UV protection, increasing the cost and reducing the reliability of many products.

In the s, the global community decided to do something about ozone depletion. With growing evidence that CFCs were damaging the ozone layer and understanding of the many consequences of uncontrolled depletion, scientists and policy makers urged nations to control their use of CFCs.

They are the first international environmental treaties to be universally endorsed by nations of the world. The Vienna Convention for the Protection of the Ozone Layer was adopted in and entered into force in Nations that signed the Convention — called the parties — agreed to research and monitor the effects of human activities on the ozone layer and to take concrete action against activities that are likely to have adverse effects on the ozone layer. The Convention did not require countries to take specific actions to control ozone-depleting substances.

The specific actions are spelled out by the Montreal Protocol. The landmark agreement was signed on 16 September — marked globally as the World Ozone Day - and entered into force in The Protocol provides a set of practical, actionable tasks to phase out ozone-depleting substances that were universally agreed upon. The Protocol is unique in having the flexibility to respond to new scientific information. Since its inception the Protocol has successfully met its objectives, and continues to safeguard the ozone layer today.

Although the Montreal Protocol was designed to phase out the production and consumption of ODSs, some replacements of these substances, known as hydrofluorocarbons HFCs , have proven to be powerful greenhouse gases. In fact, some HFCs are more than a thousand times more potent than carbon dioxide in contributing to climate change.

After several years of effort, the parties agreed on 15 October to amend the Protocol to include control measures to reduce HFCs the Kigali Amendment.

A successful HFC phasedown is expected to avoid up to 0. The Vienna Convention, Montreal Protocol and Kigali Amendment create a global policy framework for protecting the ozone layer and the climate. Implementing those policies has required profound changes in many commercial and technological sectors. Putting policy into practice. Refrigeration and air conditioning were major users of CFCs.

Under the Montreal protocol, CFCs have been completely phased-out. The Kigali amendment is now stimulating a further shift towards low global warming HFCs or alternative coolants, such as hydrocarbons or ammonia. This shift to new coolants has also allowed manufacturers and users to switch to refrigeration and air conditioning systems with more efficient energy use.

In the s, almost all the foams used to insulate buildings, refrigerators etc. The rapid and complete phase-out CFCs in aerosols was one of the most recognised achievements of the Montreal Protocol. However, affordable CFC-free alternatives for all inhaled treatments have been developed and are now available worldwide. The most potent ODSs controlled under the Protocol - halons - are used in fire protection.

Halon production has been phased out since However, one remaining challenge is that halons produced before are still used for fire protection in civil aviation.

Methyl bromide is a potent ODS that was previously used widely to control pest and diseases, both during crop production and in food storage. The Montreal Protocol has stimulated the replacement of methyl bromide with new methods of pest and disease control that are not only ozone-safe, but also safer for operators as well.

While we still have work to do there is good news. As of now, 99 per cent of the ozone-depleting substances that are controlled under the Montreal Protocol have been phased out.

They also measure ozone-depleting substances, including some that are not controlled under the Montreal Protocol. The Montreal Protocol is widely lauded as a huge environmental success. Whilst the damage we have done to the ozone layer has not yet been undone, thanks to this agreement and the collaborative effort of nations around the world, there is scientific evidence that the ozone layer is healing itself and is expected to recover by the middle of this century.

The Montreal Protocol has also considerably reduced climate warming because many ozone-depleting substances are also potent greenhouse gases that contribute to climate forcing when they accumulate in the atmosphere. Montreal Protocol controls have led to a substantial reduction in the emissions of ozone-depleting substances over the last two decades.