Last month the US consulate-general in Shanghai began publishing their own set of air-quality figures in Shanghai - as they already do in Beijing and Guangzhou -- and it's angered a few Chinese ministers. At a press conference, Vice Minister of Environmental Protection Wu Xiaoqing made comments about "some foreign embassies" (ahem, the US) going rogue with alternative air quality readings, and how this was against Chinese law and diplomatic convention.

On their own website the US has been playing innocent, explaining that the figures are "a resource for the health of the Consulate community, but is also available through our Twitter feed for American citizens who may find the data useful," … not to mention anyone else in China with an internet connection and VPN.

Doesn't matter how you spin it, it does look a little passive aggressive. Kind of like sending your kid to a friend's sleepover party with their own smoke alarm.

But never mind the bigwigs pushing each other around in the diplomatic playground, what's important for you and me is why the figures are different, and which set do we believe?

The central problem is that both figures are showing us different things, with different interpretations.

Here's a screenshot I took at 3pm today from the China Air Pollution Index, an iPhone app that draws data from both the U.S. Embassy and China's Ministry of Environmental Protection and compares them side to side.

The big figure in each window is basically a layman's number for how bad the air is. How that number is calculated, however, can differ.

The US's Air Quality Index (AQI) is a translation of hourly PM2.5 readings from a station at the US Embassy. A reading of PM2.5 203 ug/m3 equaled an AQI of 251.

China's Air Pollution Index (API) is taken from the highest pollutant reading averaged from the day before, out of NO2, SO2 or PM10. In this case PM10 was the highest of the three, and a reading of PM10 262 ug/m3 equaled an AQI of 156.

We have three critical differences happening here:

US AQI draws from PM2.5, while China's API doesn't.

Both the US and China are publishing hourly PM2.5 data from two different stations in Beijing. But China argues that this isn't enough to gather truly accurate data, you instead need to have several stations set up across the city. Hence the two use different pollutant sources to derive their AQI/API.

US and China don't calculate their AQI/APIs the same way.

Using these two sites to make the calculations, let's take the current figure of PM2.5 which is 250 ug/m3.

  • China's API equates this to 300, or "heavily polluted".
  • US's AQI equates this to 300, or "very unhealthy".

No problems here. But what if the PM2.5 is at 150ug/m3?

  • China's API equates this to 100, or "moderate".
  • US's AQI equates this to 200, or "unhealthy".

It appears that in the mid-range of the figures, the interpretations suddenly differ.

China argues that because it is at a different developmental stage, it needs to be cut a little slack. And the World Health Organization does, in fact, offer different air quality gradings: a country can start at interim target one, and keep moving through the stages until they feel they're ready to start reaching for the WHO's "official" air quality guidelines. Although in these they don't propose possibly misleading terms in regards to whether a level is "healthy" or "unhealthy".

Whatever the case, in a recent Greenpeace report ranking 28 economic powerhouse cities in China, including Beijing, Shanghai and Guangzhou, all failed to meet even the lowest WHO air-quality stage (interim target one) in 2010.

US announces their "judgments" hourly, whereas China daily.

OK, forget the numbers. All you're probably looking at is the word - unhealthy, hazardous etc. But here's another critical difference. The US reading might say "unhealthy" - but strictly speaking it should say "unhealthy if you were to be exposed to this for 24 hours" - which you won't be, because every day the readings dip in and out of healthy and hazardous.

The Chinese version, however, takes an average reading of the day before. This is in line with what the US government does in their own country. (Take, for example this reading of postcode 90210 in California.)

So what should you pay attention to?

Out of all the pollutants, PM2.5 is the one you should watch out for as they're so small they're able to be absorbed deep in the lungs. So in some ways the US embassy AQI is more important. Note, it's not more accurate, but simply highlights a pollutant that's more pertinent to people's health. That said take the "judgment" that comes with the figure (e.g. "unhealthy", "hazardous") with a grain of salt because there may be some overstating.

And when all is said and done there's no denying that air pollution in Beijing is BAD. In fact, it's bad in almost all the cities across the eastern coastal region as a Greenpeace air-ranking report has revealed. As a citizen, protect yourself by wearing an N95 mask on smoggy days.

As for the Chinese government, our climate and change campaigner Zhou Rong recently had a few words to say on that: "What needs saving is the country's air quality, not the government's face. The environmental authorities must stop finger pointing and start taking actions that really address the issue."

Don't have an iPhone? You can still compare figures using the websites below:

Image (cc) rytc