China's wildly fluctuating (and increasing) urban air pollution is prompting some residents of Beijing to seek homes elsewhere. A look at recent air pollution data, though, suggests that most of the country's cities suffer similar problems.

Both the Wall Street Journal and The New York Times have written recently about Chinese workers and families who want to leave the country's cities in search of breathable air. The Times quotes a doctor:

“I’ve been here for six years and I’ve never seen anxiety levels the way they are now,” said Dr. Richard Saint Cyr, a new father and a family health doctor at Beijing United Family Hospital, whose patients are half Chinese and half foreigners. “Even for me, I’ve never been as anxious as I am now. It has been extraordinarily bad.”

He added: “Many mothers, especially, have been second-guessing their living in Beijing. I think many mothers are fed up with keeping their children inside.”

But it isn't just Beijing. Ever since the U.S. Embassy in the capital installed an air quality monitor and started tweeting hourly readings (see: @BeijingAir), U.S. facilities in other cities, like Shanghai (@ShanghaiAir), have followed suit. The newly public data also both inspired the Chinese government to recognize the problem and encouraged others to develop tools to track it. A group calling itself aqicn.org (Air Quality Index China) offers a real-time map.

What's interesting is the degree to which the data follow different patterns in different cities. Here, for example, are the hourly air quality data for Beijing and Shanghai over the past month. The data point tracked is the "air quality index," a measure described here.

Beijing's data fluctuates much more widely than Shanghai's. That becomes more obvious when considering the hourly average for both cities. (The data for Beijing extends a few weeks farther back than Shanghai's.)

Beijing, inland and surrounded by mountains, has much different airflow than Shanghai, on the coast. But both have unhealthy air. The air quality index labels any score above 100 as "unhealthy for sensitive groups." Anything over 150 is just plain "unhealthy." Over 200: "very unhealthy." And so on. Earlier this year, Beijing had several instances in which its data exceeded the air quality index scale.

Air quality index readings in Beijing since March 3

This diagram shows why Beijing is at the center of concern. Over the past six weeks, the city's air has been unhealthy for all residents about 60 percent of the time.

Air quality index readings in Shanghai since March 23

Shanghai's air quality, while more consistent, has still been unhealthy for all residents one-third of the time.

The differing levels and severity of the air pollution means that the country will likely have to seek different solutions in each case. Chinese residents looking to escape Beijing's pollution end up trading one problem for another.

Photo: Various degrees of air pollution on different days in Tiananmen Square.