China last week became the world's biggest air polluter, according to a Dutch government-funded environmental watchdog. The People's Republic now out-belches the United States as the world's largest producer of greenhouse gases - two years ahead of predictions.

Worse yet, thanks to prevailing wind patterns, a lot of China's pollution ends up here: As much as 40 percent of the air pollution our own West Coast states breathe originates in China.

The air's so bad in Beijing, it's rumored that some teams are making plans to do last minute training tune-ups for the 2008 Olympics in Asia, but outside China, so they can acclimate to Beijing's time zone while avoiding the smog as long as possible.

Overall, China has 16 of the world's 20 most air-polluted cities. In some, the air carries twice the pollutants considered safe by the U.N.'s World Health Organization, causing as many as 400,000 premature deaths a year due to respiratory disease.

The World Bank has called north-central China's coal town Linfen the world's most polluted city. Coal dust hangs so heavy in the air there that cars need to use their headlights during the day.

In Beijing, the unofficial air quality index is known as the "building index." That is, how many buildings you can see down the street before the landscape turns to a pea soup-like gray fog.

Coal is the main source of those pollution "exports''; China is the world's largest producer and consumer, relying on the fuel for 70 percent of its energy/industrial needs. And coal-fired plants emit carbon dioxide (CO2), sulfur dioxide, nitrous oxide, mercury and dust. China already produces 25 percent of world mercury emissions and 12 percent of CO2.

And the pollution problem is on track to get worse.

Beijing plans to build 50 to 100 new coal-burning power plants a year - that's one a week - until 2012. That expansion will outstrip all the possible gains envisioned under the Kyoto environmental treaty.

There's also vehicular pollution. China has only 20 million vehicles on the road today, but expects that to skyrocket to 150 million to 300 million by 2020, dumping tons of additional CO2 into the air.

The People's Republic is also the world's largest emitter of black-carbon soot, the gray haze in vehicle exhaust. Soot blocks sunlight - and may be responsible for a 30 percent reduction in Chinese crop yields.

China's air-borne pollution not only plagues its crops, waters and forests, it pelts neighboring Japan and the Korean peninsula, too. Meanwhile, the winds bring considerable carbon dioxide, sulfur dioxide and mercury to America.

While the East Coast isn't immune, the West Coast is particularly hard hit. Sensors in the Sierra Nevada Mountains have identified huge Chinese pollution clouds that cross the Pacific Ocean to the United States.

In California, Oregon and Washington, sulfur from China alone reaches 10 percent to 15 percent of the EPA's allowable levels. Overall, researchers believe a third of California's air pollution (and a fifth of Oregon's) originates in China.

Chinese pollution is basically nullifying the western states' environmental progress - and their ability to meet federally mandated Clean Air Act requirements.

Unfortunately, Beijing's unswerving focus on economic development has made China unwilling to commit to curbing emissions. Premier Wen Jiaobao has made informal pledges of cuts - but in the end delivered only increased pollution levels.

One thing the United States can and should do is offer help:

* Over the next 20 years, half the world's new buildings will be built in China. We should share expertise so that those buildings will be energy-efficient - that's a productive way to reduce energy consumption and pollution.

* We should work to open the Chinese market to energy-efficient American industrial and consumer goods. It will help reduce emissions - and maybe put a small dent in our $200 billion annual trade deficit with China.

* The United States should also push to export smokestack-scrubber technology and clean-coal technology. We can't stop China from erecting new coal-fired power and industrial plants; we can help reduce the resulting dirty emissions.

In the end, a growing Chinese middle class will be the most potent force for clean air and water. But that stratum of society is only 80 million out of 1.3 billion people now. We can't wait for China to "grow out" of its polluting ways - we need to encourage progress now.