Breathless in Bakersfield: is the worst air pollution in the US about to get worse?

In California's Central Valley emissions from oil refineries and agriculture make Bakersfield America's most air-polluted city. Activists fear the Trump administration could undo small but steady improvements

The bluffs on Panorama Road offer a wide view of the northern half of Bakersfield, which is one of the few major population centres in California's Central Valley - perhaps the US' leading agricultural motherlode.

It's a rare bird's eye vantage point of this low-slung farm city of roughly 375,000 people, nestled in a bowl created by the Sierra Nevada mountains to the east and part of the California Coast Ranges to the west. On a clear day, the state's dominant topographical features put the landscape, and one's place in it, in sobering perspective.