Here’s how bad the air pollution is in Zhengzhou: Last weekend, residents lined up for the chance to inhale fresh air from 20 blue bags that were shipped to the city as part of a tourism promotion.

A travel agency sent the bags filled with air from Laojun Mountain, about 120 miles from Zhengzhou. The promotion was designed to get residents of the smog-choked city to visit the scenic mountain and breathe its pure air.

Locals donned facemasks and sucked in air from the pillow-size bags that hung from an overhead pole. According to the state-run China News Service, one pregnant woman said she felt her baby move when she inhaled.

“I would love to walk in the mountain’s forests after my child is born,” she said.

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Zhengzhou was recently ranked as one of China’s 10 most-polluted cities. Residents often wear breathing masks and the sun is usually blocked by a thick coat of smog.

Others are also using gimmicks to cash in on the pollution problem.

Guizhou, a mountainous province in southwest China that boasts about its pristine atmosphere, announced last month that it’s going to produce cans of fresh air to sell to tourists.

Filthy air in China is no joke, though. It’s become such a serious problem that the country’s premier recently declared “war on pollution.’’