TOKYO — Tokyo and Beijing would seem to be similar mega-cities, but in fact they’re quite different. Although both are full of cars—Tokyo with 3.8 million and Beijing with more than 5 million — the Japanese capital has much cleaner air. I’ve just arrived, and despite being downtown amid whizzing traffic, I’m breathing easily.

The big difference is that Japan got started early in curbing emissions — 14 laws alone were passed by the legislature in what is called “the Pollution Diet of 1970,” with dramatic results. Japan’s cities now have the cleanest skies in Asia. As the photo below shows, Tokyo still has the traffic, but not the smog problems.

But what Japan did more than 40 years ago, China is doing now — partly in answer to some vigorous citizen protests against polluting plants and spewing cars. The Chinese government appears to be listening, at first closing (at least temporarily) more than 100 emission-heavy factories, then promising to cut air pollution 25 percent by 2017, and now beginning the more challenging task of addressing traffic problems.

It's a big deal when the Chinese government actually admits it has problems. “China indeed is suffering from severe air pollution,” said Xie Zhenhua, vice chairman of China’s big economic planning commission. He added that fossil fuels are at the root of the problem.

It’s about to become much harder to register a new car in Beijing, thanks to a new government edict that will cut the quota of license plates it gives out annually 37.5 percent from 240,000 now to 150,000 by the end of 2014. In 2017, only 90,000 new cars will get licensed, Beijing said, though clean fuel vehicles will be OK. The total number of vehicles in the city will be capped at 6 million.

Chinese officials award plates in a lottery system, so the new edict has set off an intense push by car owners to get selected before the boom falls. In July, the Wall Street Journal reports, 18,400 licenses were issued, but 1.5 million applied. Shanghai and Guangzhou are also limiting car registrations, for both air pollution and traffic congestion reasons.

The Chinese need to take these draconian steps. Beijing is so severely wreathed in smog that visibility can shrink to 65 feet. Some 16 Beijing highways have been shut down for that reason. Particulate matter, from diesel car exhaust and other sources, is a big health threat as a known carcinogen. Here's a closer look at the air pollution problem on video:

So Beijing plans to allow 600,000 new cars on its roads by 2017, but 170,000 of them are to be battery electric, plug-in hybrid or natural gas cars. The net result of all this will be, finally, cleaner air for Beijing, with free-breathing Tokyo as a good Asian model.

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