Randy Wewers, Richard Willis, Dolores Scamardo, John Scherrey, Jean Hahn, Fred Schwartz, Reba Sullinger, John Heide, Nancy Cullen, Sondra Tompos, Donald Yandell
There are several reasons for the flattening of nitrogen oxide levels including hard-to-reduce industrial and truck pollution, said study co-author Helen Worden, a scientist at the National Center for Atmospheric Research in Boulder, Colorado.