The air quality in most of America's major cities, Los Angeles notwithstanding, is largely safe. However, within many major former industrial cities—especially those split along racial and class lines—there exist neighborhoods of largely lower-class black and Latino residents who are subject to far worse air pollution than many of their neighbors.

For instance, in Chicago, which has the highest amount of air particulates of any large American city, residents of majority-Latino neighborhoods Pilsen, Little Village, and the far Southeast Side have been fighting—with mixed success at best—against polluters and the city bureaucracies that have allowed them to pollute neighborhoods for decades. Far Southeast Side residents successfully got a Koch Industries-owned petroleum coke refinery to skip town and pay a settlement, but the settlement only amounted to some $60 per resident.

Seven of the 10 worst cities in America for air pollution are in California, per the American Lung Association. The two worst—Bakersfield and the Visalia-Porterville-Hanford metro area—are trending down. The two bear much of the attack that California's drought is waging on the state's air quality. Their location at the southern tip of the Central Valley, where the sun beats down unobstructed, creates an "inversion layer" of warm air, trapping industrial chemicals beneath it.

China leads the world in deaths linked to air pollution, with some 1.6 million a year. (India has 1.3 million.) Burning coal, China's main source of energy, is the main culprit. A recent peer-reviewed study linked the industry directly to over 360,000 deaths a year, or about 22 percent of the total.

In 2013, Xi Jinping's government published a five-year plan that would curb coal emissions. It also eased restrictions on media reporting on the pollution crisis, and earlier this year ratified the Paris Climate Agreement. However, loopholes in Xi's policies and existing projects put the Chinese government on track to open an average of one coal plant a week for the next four years, found a Greenpeace report published earlier this year.