Superstition Is Making Beijing's Air Pollution Even Worse

​There are a lot of things contributing to the record-level air pol​lution suffocating the capital of China, but there's one factor making an impact that you might not have considered: good, old-fashioned superstition.

After the Olympics in 2008 (during which Beijing cut its traf​fic in half by alternately banning odd-number-ending license plates and even-number-ending plates) the city introduced a longer term traffic ban based on the last number of each license plate. Every plate in the city ends with a number between 0 and 9, so each day during the workweek, two ending digits are banned from the road between 7 AM and 8 PM (on Monday, license plates ending in 1 and 6 are banned, for instance).

Here's the problem: on one day of the week, the number 4 is banned. In Chinese numerology, the number 4 is very unlucky (it sounds a lot like the word death, so, understandably people avoid it). Because of this superstition, a lot of people reject license plates ending in 4.

So since there aren't as many "4" cars registered in Beijing, the ban doesn't take as many cars off the road as it does for other numbers. Nan Zhong, a PhD student in the sustainable development program at Columbia University, wanted to find out whether this makes a noticeable impact on the air quality, traffic congestion, and public health. Though her research has not been published in a peer-reviewed journal (Zhong told me she's in the process of submitting it at a few publications), she presented her findings Thursday at the school's symposium on sustainable development.

Zhong got data on the number of cars in each license plate category from the local government and found there are indeed notably fewer cars on the day 4 is banned (along with 9):

Zhong then compared the traffic congestion, air quality, and local ambulance calls on days when "4" cars are banned to all other days of the week. She found there were roughly 10 percent more vehicles on the road on "4" days, but traffic congestion was 20 percent worse than any other day of the work week. The level of nitrous oxide in the air was 12 percent higher.

As for ambulance calls, Zhong looked specifically at calls for heart problems and fever and discovered that they increase three percent and 11 percent, respectively, on days when "4" cars were banned compared to other weekdays.

"I don't think the officials thought of this when they first introduced the policy," Zhong told me, adding they're now aware but have no plans to change the policy. "Number four is an unlucky number, but there are lucky numbers. One possible solution would be to combine unlucky number four with a lucky number to try to balance it out."

In the scheme of things, the superstition around the number 4 is just a drop in the bucket for Beijing's air quality troubles. The effectiveness of car bans have been questioned flat out, with researchers sugges​ting drivers can get around bans by buying cheap, inefficient vehicles with different license plate numbers. And Beijing's air quality continues to sit at unhealth​y levels on a daily basis, even with an effort to reduce the number of cars. But having a once-a-week ban on cars that basically aren't on the road anyway definitely isn't doing the city any favors.