In a surprise to scientists, gains in tackling dirty air have stagnated

In the 1950s, Los Angeles residents raised signs protesting the region's filthy air. One woman's sign, at an anti-smog committee meeting in 1954, mocked that Los Angeles' San Gabriel Valley had been transformed into the inhospitable "Death Valley." 

Largely due to car pollution, many American cities had indeed become ridden with highly visible air pollution, or smog, which grew worse over the next few decades until the U.S. Environmental Protection Agency (EPA) was created, along with the Clean Air Act, in 1970. The Clean Air Act, backed up by EPA enforcement, was strengthened in the decades that followed. Read more...

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