In this photo taken April 25, 2011, cars clog a main thoroughfare in Beijing, China. (Ng Han Guan/AP)

On Monday, China published a new policy document that revealed plans to take more than 6 million older vehicles off the roads in a bid to fight the country's notorious air pollution problem. The scale of the plan is certainly impressive: That's more than the total number of registered vehicles in the entire country of Switzerland, for example.

But can limiting the number of cars alone really hope to significantly improve the air quality in major Chinese cities? It's not the first time China has toyed with the concept: During the 2008 Beijing Olympics, Beijing experimented with banning cars with certain license plates from the roads on specific days. That tactic was rolled out again as the city's pollution problem gained steam last year.

While studies have shown some success from these measures, the fact that this bigger ban is being proposed (with 330,000 cars being decommissioned in Beijing alone) is perhaps a sign it wasn't enough. And the evidence from other cities is that similar "license plate schemes" may have failed: France was forced to abandon a similar scheme it attempted this year, and research from Mexico City suggests that people often buy cheaper, less efficient cars with different license plates in an attempt to get around the bans (there's a lot of evidence that Beijingers have managed to flout the rules, too).

What's different about the new plan is that it involves decommissioning cars, not just banning them from the road on a certain day. It's hard to predict how it will be implemented, however. Reuters notes that – in theory – Beijing already bans the high-polluting "yellow label" vehicles that would be decommissioned from its roads, but officials have admitted they don't have the ability to stop all of these vehicles from being driven in the city. Even when vehicles are "decommissioned" in China, that may not be the end of them: Shanghai Daily reports that studies show 60 percent of cars taken off the road in China end up driving again in rural and remote areas.

Ultimately, as impressive as taking 6 million cars off the road is, it's a drop in the ocean when you remember that China has 240 million vehicles on the road, and that 17.9 million vehicles were sold last year. And these vehicles may not even be doing most of the polluting: A 2013 study from the Chinese Academy of Sciences found that "industrial pollution" was the main cause of Beijing's smog, and that car exhaust (plus the burning of trash) was only causing about 4 percent of the smog. While a more recent study from the Beijing Environmental Protection Monitoring Center found that automobile exhaust was a bigger problem (31.1 percent), its ultimate conclusion was the same: Heavy industry outside the city was one of the biggest problems for the city's air quality.

Ultimately, China's plan to take 6 million cars off the road sure sounds like an enormous step forward. In reality, it's only a small part of what will need to be a far broader strategy to improve China's air quality, and a sign of how enormous the scale of the issue is.