The U. S. haze patterns and trends since 1960 are presented in 16 haze maps that represent four time periods and four seasons. The overall national view shows two large contiguous haze regions, one over the eastern U.S. and another over the western Pacific states.
Cascade mountain ranges.
The most dynamic pattern can be observed over the eastern U. S. extending from the Mississippi River to the East Coast. The remarkable reduction in the cold season haziness and the strong increase during the warm season has shifted the haze peak from winter to summer. Consequently, there was also a regional shift in highest haze pattern. In the 1960s the worst haziness occurred surrounding Lake Erie and the N.Y.- Washington megalopolis during the cold season. By the 1990s the worst haziness has drifted southward toward Tennessee and Carolinas and it now occurs in the summer season.