More-efficient new vehicles and stricter emissions standards can help reduce air pollution, but the effect is limited if older, dirtier cars remain on the road in large numbers.
Now, the Chinese government plans to take 6 million of the country's worst-polluting vehicles off the road this year, the Associated Press reports.
The order--which also requires gas stations to sell only the cleanest grades of gasoline and diesel--will "phase out" vehicles from before the 2005 model year that do not meet stricter emissions standards.
The plan calls for the removal of 5 million older vehicles in Beijing, the nearby port of Tianjin, the Yangtze River delta, around Shanghai, and the Pearl River delta, around Guangzhou.
Officials did not say where the remaining 1 million vehicles slated for retirement are located.
Cadillac in China
Last year, China became the first nation to surpass 20 million new-car sales in a single year.
But its soaring vehicle population has come alongside staggering levels of air pollution, though vehicle emissions are thought to account for roughly one-quarter of the total smog produced in the country.
The government has tried to combat environmental hazards with stricter emissions and fuel-economy standards.
China uses the European system of emissions standards; Euro 4 standards took effect in the country in July 2013, and the stricter Euro 5 standards will follow on January 1, 2018.
In addition, new fuel-economy rules will require new passenger cars to achieve 34 mpg by 2015, and 47 mpg by 2020.
The government is also encouraging the mass adoption of electric cars, although this policy has been met with buyer resistance.
Meanwhile, at least one Chinese city has already implemented a version of the national government's plan to scrap older cars, on the streets that it controls.