"A conservation group found 36 U.S. national parks had moderate or worse levels of ozone pollution in a report card released on Tuesday, with four parks in California receiving the worst grades for health effects.

The National Parks Conservation Association study singled out Sequoia, Kings Canyon, Joshua Tree and Yosemite national parks with "F" grades in the report's "healthy air" category for ozone pollution.

In part, that is because those four parks in California, like other parts of the state, suffer from geography that traps air pollution in vast basins or valleys, said Ulla Reeves, who manages the nonprofit group's clean air campaign."

Alex Dobuzinskis reports for Reuters July 28, 2015. [2]