Roughly half of everyone alive in the U.S. today has never experienced really bad smog.

Those over, say, age 45—big-city residents and Angelenos especially—may recall hazy days in which the sun was barely visible, and air that actually tasted metallic.

It's a memorable experience, and it's why the future of electric cars increasingly rests in China.

DON'T MISS: China's BYD tops global electric-car production for third year in a row

It's long been government-industrial policy in the world's most populous country to dominate global sales of photovoltaic solar cells, lithium-ion battery cells, and plug-in electric vehicles.

But one powerful motivator for upcoming changes to the Chinese vehicle fleet is the hazardous level of air pollution in most major Chinese cities.

That smog comes from sources that the U.S. tackled decades ago: coal powerplants without smokestack controls, industrial plants venting vapors, and primitive diesel engines in delivery trucks.

Traffic in China

Traffic in China

Separate from smog-causing particulates, carbon monoxide, nitrogen oxides, and hydrocarbons is the country's determination to reduce emissions of carbon dioxide, the major contributor to soaring atmospheric carbon that have led to climate change.

That aligns neatly with the government's intention to catapult its auto industry beyond those of North American and European makers, as Bloomberg laid out last Friday in a fascinating article titled, "China's War on Pollution Will Change the World."

It's worth reading the piece in full, and studying its infographics, to appreciate the nature of the problem.

CHECK OUT: China plug-in electric vehicle sales in 2017: almost 4 times those in the U.S.

"Four decades of breakneck economic growth turned China into the world’s biggest carbon emitter," write authors Jeff Kearns, Hannah Dormido, and Alyssa McDonald.

"But now the government is trying to change that without damaging the economy," they continue, "and  ... use its green policies to become a leader in technological innovation."

Less examined is why the government's concern over potential social unrest stemming from foul air and its health effects has led to many of these actions.

Street-level smog in Beijing

Street-level smog in Beijing

How bad is the air pollution in China? So dire, according to the Berkeley Earth research group, that it was a factor in 1.6 million deaths in China ... in a single year.

But over the past two years, carbon-dioxide emissions in China have fallen slightly.

The government has axed plans for new coal powerplants and closed dozens of operating ones, though a cold winter that led to shortfalls in the alternative fuel—natural gas—saw some of them reopened.

READ THIS: China axes 103 coal-fired power plants, citing smog, overcapacity

Cars with no tailpipe emissions are just one facet of a multi-pronged war on sources of air pollution, and diesel trucks with less-capable or no emission controls need to be a major focus as well.

But starting next year, China has adopted rules that require carmakers to sell a set percentage of zero-emission vehicles each year.

That percentage, based on a system of credits like that in California, will rise each year—but at rates California regulators can only dream about.

BYD Qin EV300

BYD Qin EV300

China is already the world's largest car market, at more than 30 million vehicles sold annually. It's become the world's largest plug-in electric car market, too, at almost four time the size of the 195,000 or so plug-in vehicles sold last year in the U.S.

By 2025, China's official goal is that 7 million of those 30-plus-million new vehicles sold will be powered by batteries.

The U.S., meanwhile, is planning to lower fuel-efficiency standards and raise the allowable carbon-dioxide emissions from new vehicles, starting in 2022.

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