Beijing’s air pollution levels have been “hazardous” or “beyond index” (by the US Embassy monitor‘s designation) for nearly three days. The city is in the midst of one of its epic, multiple-day extended pollution spells, also known as an “airpocalypse.” So what’s new or different about this one? Let’s take a look from a few angles.

A) The Data

Over the past 24 hours, the US Embassy’s monitor reported a maximum PM2.5 concentration of an incredible 886 ug/m3, certainly the highest I can ever remember. The 24-hour average was reported as 568.5 ug/m3. This 24-hour average can be compared against the Chinese, US, and recommended WHO 24-hour PM2.5 standards, which are 75 ug/m3, 35 ug/m3, and 25 ug/m3, respectively. So, the daily average pollution in Beijing was 7.6, 16.2, and 22.7 times over the standards in China, the US, and the WHO’s recommendations. That is certainly the worst 24-hour period I can remember, though I haven’t been tracking the data recently as closely as I used to.

What about Chinese data? Last year, Beijing began publishing hourly PM2.5 data; real-time monitoring was extended to 74 cities beginning this year. What do the Chinese data say? Well, there are two sites for checking real-time data. The Beijing Environmental Protection Bureau runs its own network of monitors and publishes the results at http://zx.bjmemc.com.cn/. The user interface is terrible, but I was able to see that the Agricultural Exhibition Center station – not too far from the Embassy – reported a PM2.5 concentration of 699 ug/m3 at 1am on 1/13/13:

The Embassy reported 731 at the same time. These are comparable enough. Not much consolation given the poor state of the air quality, but nice to know that the Chinese real-time PM2.5 data reporting system seems to be tracking the Embassy’s. This is major progress compared to, say, a year ago.

The second monitoring network is run by MEP’s China National Environmental Monitoring Center. The interface for their real-time reporting site, http://113.108.142.147:20035/emcpublish/, is also terrible, but if you click through to Beijing you find it currently re-directs data for Beijing to the BJMEMC site. It’s nice to see these groups coordinating their data (which was not always the case), though it’s still not optimal to have the two systems with two interfaces.

Summary: the air quality is awful – perhaps the worst in recent memory. But at least both the US and Chinese government data more or less agree on just how bad it is.

B) The Causes

What’s causing this horrible pollution spell? Although it’s possible we’ll see some detailed studies come out in the coming months that offer some specific or concrete explanation, my guess is that this particular episode was induced by weather patterns. Some are theorizing that it’s due to more coal being burned because of the uncharacteristically cold weather. That’s possible, though I think it is unlikely that this pollution episode is caused primarily by a discrete increase of direct pollutant emissions. Pollution in Beijing is influenced by many factors, but the main ones are:

1) Direct pollutant emissions from factories, vehicles, power plants, etc. across all of Northern China. Beijing has made a lot of progress in recent years in controlling emissions within the city’s municipal boundaries, but the truth is pollution is regional. Whatever happens in all the major provinces around Beijing – Tianjin, Hebei, Inner Mongolia, Shanxi, etc., will effect Beijing. These provinces are developing rapidly – more factories, more power plants, more cars, more coal burning – and it’s making Beijing’s efforts to clean up all that much more difficult. Over the past few weeks, there may have been some increase in emissions due to the severe cold, but I don’t think this discrete increase would have been enough alone to cause a spike of 2 or 5 or 10 times the pollution in Beijing.

2) Secondary pollution. The atmosphere is quite the chemical soup. While direct emissions matter, a lot of air pollution is secondary, meaning that it is caused by directly emitted pollutants interacting with each other in the atmosphere, giving rise to new forms of “secondary” pollution. Much PM2.5 is this secondary pollution. Of course, the longer pollutants are allowed to interact with each other, the crazier and more extreme the secondary pollution will become. This bring me to:

3) Weather. Anyone who has lived in Beijing knows that the primary factor influencing a blue sky day vs. a pea soup sky day is the wind. If there are a few consecutive days where the winds are stagnant – or blowing lightly from the south and trapping pollution against the mountains in northern and northwestern Beijing – the pollution is going to accumulate rapidly. Throw in some increases in direct pollutant emissions from the cold weather, and the chemical soup starts really brewing. The result? Spikes in temporary pollution, in this case all the way above 800. I can’t put my finger on a site right now that can show the air trajectories in northern China over the past few days, but I would be very confident they are showing stagnant air in and around Beijing.

Don’t misinterpret me; I’m not blaming the weather for Beijing’s pollution. Clearly the long-term solution has to be to reduce direct pollutant emissions, as policymakers can’t control atmospheric or weather conditions that give rise to secondary pollution and accumulating pollution spikes. But if you want to point to a discrete reason why there is a spike right now, I think you have to point to weather patterns suboptimal for pollution dispersion, possibly confounded by slight increases in regional direct emissions due to more coal burning for home heating.

C) The Politics

It will be interesting to see the Chinese government’s reaction to this episode. We already have one depressing reaction – Xinhua’s tweet about the “fog” – though no one’s buying it and it’s hard to believe they can get away with this sort of spin much longer. What is more interesting to me is the unfortunate timing of this pollution event. After all, the Chinese government has just racked up a couple of positive wins in air pollution control, specifically:

1) December 5, 2012: MEP last month just released a major regional air quality improvement plan (《重点区域大气污染防治“十二五”规划》), which, for the first time, calls for specific reductions in ambient pollution levels in key cities for a variety of pollutants including PM2.5, and requires cities to develop plans to meet these reduction targets. More on this in a separate post, but it represents a major step forward in comprehensive, integrated, regional air quality management.

2) January 1, 2013: MEP just begain releasing real-time PM2.5 data for 74 cities, a major first step towards data transparency that should be lauded as progress. Although this is only the first step (see Ma Jun’s nice article on this, “We’re winning the air pollution data battle – so what next?“), it is unfortunate that MEP couldn’t bask in a little bit of positive public reaction prior to being slammed with the current pollution crisis.