Ultraviolet radiation (UV)

is the energy range just beyond the violet end of the v:isible spectrum. Most UV :is blocked by earth's atmosphere (particularly the stratospheric ozone layer) but some solar UV penetrates and aids in plant photosynthes:is and the production of Vitamin D in humans. Too much UV can burn the skin, cause skin cancer and cataracts, and damage vegetation. Volatile Organic Compounds (VOCs) are precursors of tropospheric ozone and photochemical smog. They are produced by human activities including the use of dry cleaning solvents.