Shaconage, the Cherokee name for this area, means "land of blue smoke." A smoke-like natural bluish haze, and mist-like clouds that rise following a rainstorm, inspired the name Smoky Mountains. During the growing season, the Smokies' lush vegetation emits large quantities of moisture and organic compounds. Together they form the natural haze, which is thickest on calm, sunny, humid days. But the misty veil is not all nature's work. Air pollution contributes too. In recent decades visibility in Great Smoky Mountains National Park has decreased dramatically. Because mountains tend to trap air currents, the effect of pollution on visibility and plant life is greater in the Smokies than in some other areas. Air pollution comes to the Smokies from sources both far and near. Pollutants and the problems they bring take many forms. Today many of the Smokies' plant and animal species suffer from pollution-induced impacts such as acid precipitation and high ozone.