NASA SOHO Mission,Yohkoh
science team
Ecological impacts of
UV-B radiation
Background information
What is UV-B and why do we care about it?
Ultraviolet radiation (UV) includes radiation emitted from the sun of wavelengths between 100 and 400 nm. It is divided into UV-A, UV-B, and UV-C bands. Ultraviolet B radiation (UV-B), the range of interest for the purposes of this web site, is energy of wavelengths in the range of 280-320 nm.
The electromagnetic spectrum
(http://www.arpansa.gov.au/images/nir/spectrum.gif)A small amount of UV-B is good for animals, because it allows synthesis of the vitamin D necessary for absorption of calcium and phosphorus. However, higher doses of UV-B can cause DNA damage and other negative health effects in microorganisms, plants, and animals. The direct effects of UV-B exposure on people are well documented and publicized, but less attention has been paid to the ecological impacts of UV-B, which can be severe for many forms of life over a wide range of ecosystems.
What controls levels of UV-B at the Earth's surface?
The amount of UV-B at the Earth's surface is a function of the sun's emission, and the absorption, reflection, and transmission of the UV-B as it passes through the atmosphere. If the amount of UV-B in a particular place were to be determined without considering atmospheric influences, it would be dependent upon the latitude, altitude, time of day, and position of the sun relative to the location (seasons). The closer the location is to the sun at any given moment as a result of these factors, the higher potential there is for higher levels of UV-B to reach that location. For example, a 20% increase in UV-B irradiance is associated with every 1,000 m. increase in altitude (Blumthaler et al. 1997). The level of UV-B that actually does reach a location can be quite different, dependent upon the absorptive, reflective, and transmissive properties of the atmosphere over that location. UV-B is primarily absorbed by stratospheric ozone (O3) but is also absorbed and reflected by clouds and air pollution in the troposphere, such as tropospheric ozone.
Earth's atmosphere
http://starryskies.com/solar_system/Earth/atmosphere.jpgOzone depletion and UV-B
Depletion of the ozone hole has been occurring gradually since 1980 (Fahey 2002). In the 1970's human-produced halogen-containing chemicals, including chlorofluorocarbons (CFCs), were found to cause stratospheric ozone destruction. More UV-B radiation has been measured at the Earth's surface in places where stratospheric ozone depletion has been observed (Madronich et al.1998).The Montreal Protocol was introduced in 1987 with the purpose of phasing out the use of ozone-destroying CFC's and halons by the year 2000 (Jackson 2002). Cutbacks by the first 29 ratifying countries began in 1989 and many other countries have ratified the Protocol and associated Copenhagen Amendments since then. Even with the reduction in releases of ozone-depleting substances resulting from the Montreal Protocol, the 'holes' and thinned portions of the ozone layer are expected to persist into the next century. Additonally, many other ozone-depleting substances, such as carbon tetra-chloride, methyl chloride, and methyl bromide, are still being produced and released into the atmosphere.
Ozone-damaging stratospheric chlorine/bromine for different management scenarios
http://www.beyonddiscovery.org/content/view.article.asp?a=73The purpose of this web site is to examine the ecological impacts of stratospheric ozone depletion and the subsequent increase in UV-B. Therefore, information about ozone depletion and subsequent increases in UV-B have been summarized. More detailed information can be found in web sites referenced in the links section.
