Now you can compare Beijing PM 2.5 air quality readings on your phone

It just so happens that today is not one of the more beautiful days in Beijing. After a week of generally glorious fall weather, with exceedingly clear air (except once or twice), the national holiday is over and whatever process churns up the smog has resumed.

I’m not complaining. I haven’t been here long enough to get worked up about air quality. But it did lead me to check the China Air iPhone app that delivers official Chinese government pollution readings alongside the point-source reading from the U.S. embassy. And I noticed something new.

Before*, you would see only PM 2.5 (particle matter under 2.5 micrometers in diameter) for the U.S. embassy reading, and only PM 10 (10 micrometers), sulfur dioxide, and nitrogen dioxide. The app gives indicies derived from each source’s standards, but the data weren’t directly comparable. These pollutants don’t necessarily come in tandem or in proportion.

Now, however, you can compare PM 2.5 readings from both sources. In the case of a few minutes ago, the U.S. was reading more PM 2.5 than the local government. These still aren’t comparable measures: Beijing creates a number based on many sampling stations, whereas the U.S. has one location. But there’s something to compare. If you trust the measurements from the government, which seems fairly reasonable to me in this case, you could learn that the U.S. embassy is in an unusually polluted part of town right now.

One superficial reason to take the new Chinese data seriously is that a government official has said we should not expect air to be super clean for quite some time. According to a Xinhua article (in Chinese), the city’s 20 new PM 2.5 sensors are expected to find particulate content over their standard of 150 mg/m^3 quite regularly for the foreseeable future. (“从北京整体空气质量水平看，PM2.5浓度值超标在很长一段时间内会经常出现.”)

Seems to me this new data has been around in some forms for some months, but this is the first direct comparison I saw.

*I note that the app’s iTunes page shows data for PM 2.5, but it had been “–” since I installed the app.