Among all the recent PM2.5 news, this chart from an early January CCTV report caught my eye:
I couldn’t find this data on the Beijing EPB website to verify, so if anyone out there does find an original source please let me know. It is a little strange that numbers for 2000 and 2005 are reported, since the Beijing EPB claims to have only monitored PM2.5 since 2006, but let’s ignore that for a moment and assume that CCTV has reported this accurately. This would be the first time that I’ve seen official PM2.5 numbers reported by the Beijing EPB, so they are worth examining. Specifically, let’s look at two questions:
1) Is this declining trend correct?
2) Are these absolute numbers credible?
Let’s look at these questions one at a time. The Beijing EPB claim of declining PM2.5 concentration especially surprised me because, just two months ago, Xinhua cited a Chinese Academy of Science report suggesting that PM2.5 has been increasing 3-4% per year. A more detailed description in the People’s Daily said this trend has been occurring since 1998. I haven’t seen the original CAS report, so I don’t know the details behind the study (e.g. how many monitoring stations, locations, etc.). Nonetheless, it’s not very encouraging to see this contradiction — and one coming from a government source. Let’s see how and if Beijing EPB tries to reconcile this contradiction over the year as more and more PM2.5 data come out.
As for other data sources, I still haven’t seen any public, peer-reviewed studies that show clear long-term PM2.5 trends for Beijing. If anyone out there knows of any, please let me know by e-mail or the comments. My hunch is that the few research teams out there (e.g. universities) who do have continuous PM2.5 monitoring data over a long time series are unwilling to publish them because those data are fairly sensitive, but I may be wrong.
In the absence of clear long-term trend studies, all we have are a few snapshots in the literature. Many reports just cover one or two monitors over a limited time. Still, let’s take a look at the reports as a way of gauging the credibility of the Beijing EPB-reported data. In other words, how do the Beijing EPB-reported PM2.5 numbers compare against the few other independent PM2.5 estimates we have?
Well, the first obvious place to look is the US Embassy’s monitor. The Twitter feed from the US Embassy’s PM2.5 monitor only reports hourly and daily values, although both the new foggybeijing site and Steve Andrews’ chinadialogue piece both present annual summaries suggesting that the annual average PM2.5 from that monitor was around 100 ug/m3 in 2010-2011. This is significantly higher than the Beijing EPB 2010 figures of 70-80 ug/m3. So, we have one dissenting data point, but remember it’s only one point. The Beijing EPB could easily (and perhaps justifiably) attribute this discrepancy to the fact that their data is an average over the entire city, whereas the Embassy monitor is at a single spot in a heavily-trafficked area. We’ll have to wait and see how they explain that.
Next let’s look at some reported values in the peer-reviewed literature. Here’s a good summary “lit review”-style paragraph from Chan and Yao, 2008:
PM2.5 measurements have been widely reported in Beijing in the last 10 years. He et al. (2001) made the first comprehensive PM2.5 measurements in Beijing and reported that the annual average of PM2.5 was 115 ug/m3 at Chegongzhung (an urban site) from September 1999 to September 2000 [Vance edit: the He et al. paper also reports a second site at 127 ug/m3]. The annual average was 96.5 ug/m3 at the same site from August 2001 to September 2002 and the decrease was attributed to the air pollution control measures carried out in Beijing since 1998 (Duan et al., 2006). On the basis of measurements on selected days in four seasons, Zheng M. et al. (2005) and Wang J. et al. (2004) reported annual averages of PM2.5 in 2000 and in 2001 of 101.4 mg m3 and 109.6 ug/m3, respectively. Wang Y. et al. (2005a) reported that the average of PM2.5 from 2001–2003 was 154.3 ug/m3, significantly higher than the values reported by the other studies mentioned above.
One more I found in addition to this was Yang et al. (2011), who reported PM.5 values around 2005-2006 of 118.5 ± 40.6 ug/m3.
So, we can summarize our brief data investigation as follows:
I must emphasize very clearly that all these data are not directly comparable; I present them here merely as a first-order snapshot of the PM2.5 levels at various times and places around the city. (To give a sense of how variable the levels can be across the city, consider this quote from Yang et al., 2001: “In Beijing, annual average PM2.5 concentrations varied by 50 ug/m3 (near three quarters of mean concentration at the rural site) between the paired rural/urban sites over a distance of 70km.”) But it does seem as though many of these reported PM2.5 levels are higher than what the Beijing EPB has claimed (via CCTV), and that no clear trends are visible.
A (brief) review of independent literature studies does not immediately support the Beijing EPB’s reported PM2.5 numbers and declining trend for Beijing. In addition to several individual data points showing higher PM2.5 levels, it’s concerning that there is a Chinese Academy of Sciences study that apparently shows an increasing trend of PM2.5 — the exact opposite of that claimed by the Beijing EPB. However, with such limited data, we can’t really say comprehensively or definitively whether the Beijing EPB data are valid or not. The only thing I can say 100% conclusively is that I’m eagerly awaiting the release of more data that back up their claims (or, alternatively, the public release of more clear long-term PM2.5 trend studies from independent research groups).