Tree rings tell the story: Something's killing red spruces in New York's Adirondack Mountains. A core taken near Mount Marcy by Dr. Edward Cook (above) of the Lamont- Doherty Geological Observatory shows normal growth rates until the mid-1960s, when rings start to narrow (below).

Some scientists believe air pollution may have contributed to this decline. Dr. Cook theorizes it may have resulted from abnormally hot summers and cold winters. A similar weather pattern coincides with massive red spruce losses during the 1870s. An infrared view of Mount Marcy in 1984 (below) shows dying spruces as blue-gray instead of a healthy red.

 
Where there's smoke, there may also be toxic pollutants. At a warehouse fire in Elizabeth, New Jersey, firefighters (above) put on breathing units to protect themselves from dangerous gases. A special team had earlier identified hazardous chemicals in the fire. Detonations hurled explosive aerosol paint cans at the firefighters like hand grenades.
 
   
 
Airborne toxics can also escape in much quieter ways. At a petroleum refinery in Marcus Hook, Pennsylvania, environmental engineer George Keegan (above) tests valves for leaks of benzene, as required by federal law. Thousands of other chemical compounds in the United States - many suspected of causing cancer -- remain unregulated.