Incredible! The State Department has released six years of hourly PM2.5 data from the US Embassy in Beijing. The data is actually wonderfully well-organized (kudos to whoever formatted it and prepared it for release!), and is just begging to be dug through. Here are some initial discoveries and thoughts based on a few hours of playing around with the data. (See also some good initial analysis from Wayne Ma/WSJ here and here.)

The Dataset
The dataset contains nearly 50,000 hourly readings from April 8, 2008, to March 31, 2014. There are some gaps in the coverage, but overall the data are fairly comprehensive. (It’s also clear that the reliability of the monitor – or maybe the reliability of maintenance – improved over time.) The data are exclusively hourly PM2.5 readings from the single monitor at the US Embassy. Because the data are in hourly concentrations of PM2.5, they must be processed into daily average concentrations and then converted to AQI. There are no ozone data, nor data from other monitors around the country or world. (Yet.)

The Best and the Worst
- Best hour: 9/28/2012 at 9am and 2pm: 0 ug/m3. Astonishing!
- Best day: 9/28/2012: 3 ug/m3
- Worst hour: 1/23/2012 at midnight: 994 ug/m3
- Worst day: 1/12/2013: 569 ug/m3
- Biggest single-hour change: 11pm to midnight, 1/22-23/2012: +769 ug/m3
- Longest streak of Unhealthy air (>150 ug/m3): 161 hours (2/19-26/2014)

Yearly Averages
The following figure shows Beijing’s yearly average PM2.5 levels according to the US Embassy monitor. Also shown on the figure are the US annual average PM2.5 standard (12 ug/m^3) and China’s (35 ug/m^3).

The data, of course, show that Beijing’s air quality is atrocious, with annual average PM2.5 many times higher than recommended levels. But what about the trend? Well it’s actually not clear. Obviously the first quarter of 2014 has been terrible, but that could be just the season (see next graph). 2013 was slightly worse than 2012, but that’s not a trend; 2012 may have been abnormally clean. Overall, it looks like Beijing’s air has not gotten demonstrably worse or better over the past six years.

Monthly Averages
From these data we can take a first look at seasonal periodicity in PM2.5. This graph shows monthly average PM2.5 levels over the entire dataset (note: I should really show error bars in this, but don’t have the time to put that together right now and anyway this isn’t peer-reviewed, just a quick look):

This is a strange pattern that I’m not sure how to interpret. It does seem to make intuitive sense that the winter months would be worse, but why also June and July? Perhaps the answer lies in the weather and wind patterns of the spring and fall that help disperse pollution, but that’s just a guess.

Let’s look at the entire time series (monthly averages):

This is way less clean/clear. The extreme variability of the monthly air quality jumps out immediately, especially January 2013 and February 2014 (worst months), as well as January 2011 (best month).

Hourly Averages
Ever wonder how Beijing’s pollution changes over the course of the day? Well, take a look:

I’d say that looks like a pretty clear trend, with PM2.5 surging during evening rush hour and remaining high into the early hours of the morning. Is this linked to motor vehicle patterns (including trucks entering the city at night?) or related to diurnal weather patterns? I’m not sure yet, but certainly worth closer look and investigation.

Categories
Finally, at the risk of showing too much in one table, here’s the percentage binning of days by US AQI category in each of the years (further description of these bins is here).

As also noted by Wayne Ma in WSJ, nearly half of the days are deemed “Unhealthy” by the US EPA. (I haven’t compared these yet against the Chinese scale, as Wayne did.) It’s clear that Beijing and the national government have a lot of work left to do. But really we knew that before we had 50,000 data points to prove it.

Next Steps
I get asked all the time by researchers if I have these data; I’m so glad that State has finally put them out there public. I’ve just scratched the surface here, and I’m really looking forward to seeing the further analysis people come up with. If I have time I’ll post some more analysis this week. Now if only the Chinese National Environmental  Monitoring Center would do a similar data dump…

Well, I’ve officially been called “geeky” on Twitter. I wear the label with pride. Not wanting to let my fans down, I decided to prove my earlier conjecture that the US Embassy linearly extrapolates the AQI-PM2.5 relationship from the EPA’s 400-500 range for concentration values above 500. As I noted before, this is NOT supported by regulatory language in the US, since the PM2.5 concentration almost never goes above 500.

Here’s a plot of the US EPA’s regulatory AQI-PM2.5 relationship definition (blue, stops at 500) as well as a smattering of data from the Embassy monitor (red). Looks pretty clear that the Embassy is just using the EPA’s same AQI-PM2.5 relationship from 400-500 for all values above that.

There are lots of numbers used to describe air quality these days in China. This post is intended as a glossary to demystify the different numbers currently used by various sources.

Concentration: The most direct way to report air pollution would be the concentration of a given pollutant in the air. This is straight-forward science and measurement. Example: PM2.5 concentration is 950 micrograms per cubic meter (ug/m^3).

Although concentration is straightforward scientifically, there are a couple of problems with it from a public outreach perspective. First, not everyone understands what concentration is, or has context for what the numbers mean. Second, it’s difficult to compare different pollutants to each other, since each pollutant affects people differently depending on concentration. Therefore, concentrations are commonly normalized to some scale, on which multiple pollutants can be compared together and a single “score” covering multiple pollutants given to a city.

Confusingly, there are currently three such scales used to describe Chinese air quality: the US Air Quality Index (AQI), the current/outgoing Chinese Air Pollution Index (空气污染指数, API), and the current/future Chinese Air Quality Index (空气质量指数, AQI). Here are the technical details of each one:

US AQI: In the United States, concentrations are converted to the “Air Quality Index” using breakpoints defined in 40 CFR 58 Subpart G. (Edit 1/13/13: The EPA has just revised these breakpoints, though it hasn’t posted to the CFR yet. New breakpoints shown here and in the graph below.)

Note: the US does not define an AQI above 500. On airnow.gov, if you use the AQI->concentration calculator and input an AQI above 500, it gives an error message.

This means that AQIs reported by the Embassy above 500 are not in accordance with US regulations. My guess is that they linearly projected using the same slope as the 400 –> 500 line.

China API: China’s current but outgoing system of API uses breakpoints described in an old post of mine here. This is officially the current system in place nationwide, though it does not include PM2.5 or ozone.

China AQI: In February 2012 (regulation HJ 633—2012), China defined a new air quality index that includes PM2.5 and ozone. It doesn’t take effect nationwide until 2016, but Beijing and many other cities have already adopted it. The China AQI breakpoints are here:

Note that the Chinese system also does not define an index above 500. This is why the data reported by the BMEMC rail at 500 for AQI. I don’t think they project as the Embassy does.

Let’s do a quick comparison of the PM2.5 cutpoints in the US and in China:

Observations:
1) The US is more strict at low concentrations.
2) The systems are identical above a concentration of 150 (AQI of 200).
3) Neither system is linear, which is annoying and non-intuitive.
4) It is also very annoying that the numbers are so close (as opposed to a 1-10 index, for example). This means it is very easy to confuse AQI and concentration.

Summary
- Concentration is the most accurate way of describing air pollution, but isn’t good for public awareness and comparing multiple pollutants.
- Both the US and China use AQI systems. Both systems go from 0-500, and are not technically defined above 500.
- The US and Chinese systems are identical above an index value of 200 (PM2.5 concentration of 150), but slightly different below this level.
- Because the systems aren’t identical and have different slopes, you have to be very careful when saying something like “PM2.5 is 150.” The meaning of this statement is different depending on if you mean concentration OR US AQI OR Chinese AQI.

Confused yet?

Each year for the past few years around this time, I’ve posted an overall summary of Beijing’s annual air quality (links to 2010, 2009, 2008). Although I’ve had less time this year to update this blog regularly, I thought I would come out of hiding this weekend to take a look again at overall trends.

I won’t repeat my methodology in this post (it’s described in detail in previous years’ summaries); let’s just jump straight to the conclusions.

Using MEP’s own data, I calculate that Beijing in 2011 had a Blue Sky Day count of 286 and a calculated average PM10 concentration of 114 ug/m3. Trends of Beijing’s Blue Sky Days and PM10 concentrations are shown here:

–
Update 1/29/12: I originally posted a 2011 Blue Sky Day count of 285, along with a comment (below) that I thought the Beijing EPB’s count of 286 was an error. I concluded this based on the fact that MEP’s datacenter contains 365 data points for 2011, of which only 285 are Blue Sky Days. It turns out, though, that one day (October 28th) is missing from the data set, while another day (November 1st) is duplicated. I did not notice this in my initial analysis. The duplicated day, November 1st, was not a Blue Sky Day. If we assume that the missing day, October 28th, was a Blue Sky Day (which appears to be supported by Beijing EPB data), then the Beijing EPB’s count of 286 is correct. The graph above has been updated to account for the new Blue Sky Day total. Note that this change does not affect my calculated PM10 average, which matches that reported by the Beijing EPB.
–

The good news:
According to MEP’s data, Beijing’s annual average PM10 concentration (shown in the dark blue curve) decreased slightly from 2010 to 2011. This is a welcome change after the stagnation we saw from 2008-2010. From the perspective of this metric, it appears as though Beijing is showing some (minor) progress again in improving air quality. Also encouraging was the fact that the number of Grade I days (what China calls “excellent” air quality) went up significantly, as shown in the light blue curve in the above graph. The number of Grade I days was bolstered by an absolutely incredible January 2011, which was Beijing’s best air quality month in at least a decade.

Also in the “good news” category, though independent of analysis of MEP’s air quality data: In the last two months of the year, we saw a massive proliferation of air quality discussion among the public and in the media here unlike anything we have seen since the Olympics. Why now is not so clear – in early November I postulated that it was due to a combination of a few terrible air quality streaks in October and growing public awareness of air pollution driven by social media (see similar analysis in AFP, WSJ, and Time). Regardless of the specific reasons, the result has been incredible public pressure on the Chinese government to take more aggressive action on monitoring, reporting, and controlling air pollution, especially PM2.5. Incredibly, this pressure appears to have succeeded in driving some change: most notably, MEP has now publicly committed to a timetable for measuring and reporting PM2.5; the People’s Daily even noted, “The media called the schedule published at the end of 2011, ‘A symbol of the public opinion’s victory in the air protection battle.’” More analysis of the specific PM2.5 targets and timetables in another post.

The bad news:
Beijing’s air quality still does not meet China’s own air quality standard, and is still nearly six times worse than the recommended particulate matter target set by the WHO. In other words, the air here is still just awful. (We even saw reports this year (the first in the Chinese media that I can remember) directly linking air pollution episodes to acute health impacts and even grounded flights.)

And, although I claimed some minor progress earlier, the progress was far from consistent. Removing the data from the uncharacteristically wonderful month of January, the average PM10 concentration for February through December 2011 turns out to be 119 ug/m3 – essentially unchanged from 2009 and 2010. This directly contradicts Beijing EPB comments made at the end of January that that progress was “far from one-off.”

Even more bad news: the 2011 Blue Sky Day count exceeded Beijing’s goal of 274, but came up one day short of last year’s total of 286. This represents the first time in at least a decade that the annual number of Blue Sky Days has decreased year-on-year. (I should note here, however, that the Beijing EPB today reported 286 Blue Sky Days in 2011 – the same number as in 2010 – but I believe this to be an error. The Beijing EPB reported 19 Blue Sky Days in October, although my careful count of the data on MEP’s datacenter shows just 18 that month. I’ll keep my eye on the public statements to see if they fix this error in subsequent annual summaries.) (Edit 1/29/12: See note above regarding the resolution to the data discrepancy noted in this paragraph.)

Therefore, by China’s own currently reported data (both PM10 numbers and number of Blue Sky Days), Beijing’s air quality improvement efforts are really showing negligible progress. Even worse: Chinese data currently only cover PM10, not PM2.5, which, according to recent Chinese media reports, is actually getting worse here in Beijing. This is bad news, for a few reasons. Mainly, it’s bad news because the health impacts of PM2.5 are considerably worse than those of PM10. However, it’s also bad news politically for China, and hints at the challenges MEP will have when it begins reporting PM2.5. After claiming consistent progress for many years, how will MEP/Beijing EPB manage the fact that their new indicator shows the opposite trend?

Much more news to report on from this year, including Steve Andrews’ scathing critique of Beijing’s air quality from earlier this month, but further analysis on that will have to wait until next year.

Happy New Year everyone! Looks like it’s going to be an excited 2012 for all us air quality wonks.

In January of this year, Beijing experienced unprecedented air quality, with all 31 days being Blue Sky Days (“good” or “excellent” air quality). At the end of the month, Du Shaozhong, a Deputy Director at the Beijing EPB, claimed that this result was “far from one-off.” I disagreed, arguing that the sudden and dramatic reduction in air pollution in January could not reasonably be explained as simply the positive result of years of pollution control programs. (Although these programs have clearly had some impact, I think January’s outlier result was likely caused primarily by favorable meteorological conditions as opposed to changes in pollution sources.) Regardless, I noted that I’d be curious to see what happened in February, and what corresponding response – if any – the Beijing EPB offered.

Well, now February has passed, and the air quality results are in. Unfortunately, there is little to be “ebullient” about. There were just 18 Blue Sky Days in February (64%), and I calculated the average PM10 concentration over the month to be 144 ug/m^3. In addition to being well over twice as bad as January’s (during which the average PM10 concentration was just under 60 ug/m^3), this level is almost 50% worse than China’s own national ambient air quality standard, and over 7x worse than the WHO’s recommend annual limit.

The average was skewed by the four absolutely horrible air quality days from February 21-24, but even without considering those days, the average PM10 for the month was still 107 ug/m^3, above China’s standard and 5x worse than the WHO’s.

(As always, my data sources are MEP’s datacenter for API data, which I convert to PM10 concentration using formulas described here.)

I am still waiting for the Beijing EPB to issue their monthly air quality report, and will try to check in again once they do.

As I was writing my post yesterday, Xinhua English published a short piece on this week’s heavy pollution episode in Beijing:

BEIJING – Heavy fog with a visibility of around 1 km persisted in Beijing for a third day Wednesday, keeping the city’s air pollution at the most hazardous levels measured this year.

The municipal environment bureau’s readings indicated the heaviest air pollution on Wednesday was monitored in Daxing district in southern Beijing, where the air quality index (AQI) reading hit 362.

The AQI ranges from 0 to 500: the higher the number, the more severe the pollution. Readings over 300 are considered hazardous.

The average AQI reading for the city Wednesday was 207, down from 270 on Tuesday and 333 on Monday.

The highest AQI reading over the last three days – at 394 – was recorded in the eastern Chaoyang and northern Haidian districts on Tuesday.

The Beijing Meteorological Bureau said a weak cold front would hit the city on late Wednesday to dispel haze. Winds, however, were unlikely to completely clear the air pollution on Thursday.

The article seems fairly straightforward, though there is one very surprising detail: the terminology they are using to describe the air pollution is the United States’ terminology, not China’s. Two differences:

1) China’s own index is called the Air Pollution Index (API), not the Air Quality Index (AQI), which is what is used in the US.

2) China’s system does not use the word “hazardous” to describe index levels above 300. “Hazardous” above 300 is the US’ terminology. China’s system simply calls this “heavy pollution” (重污染), without a value judgment of the danger. (“Hazardous” might be better translated as 危险 or 有害.)

Does this shift signal the impact of the US’ Embassy’s BeijingAir Twitter feed on guiding air quality discussion, at least among the English-speaking population in Beijing, or am I reading too much into it? (I asked similar questions in two posts in 2009 when the English-language China Daily openly questioned China’s system in light of the Embassy’s data.)

Regardless, Chinese language sources appear to be uniformly using the Chinese terminology. This Xinhua article in Chinese even includes a glossary, though it carefully avoids any judgments like “hazardous,” preferring the less direct “heavy pollution” (重度污染). The article does note, though, for index levels above 300, “elderly people and those with heart or lung diseases should remain indoors and reduce physical activity…and…the general population should avoid outdoor activity.” (老年人和心脏病、肺病患者应停留在室内，并减少体力活动…一般人群应避免户外活动。)

Fresh off its unexpected best month of air quality since 1998, Beijing plunged head first this week back into mashed potato air quality. Mashed potato (scientific term, I promise) air looks like this from the ground (taken around 4pm today):

and this from space (2/20 photo from NASA):

From a data perspective, mashed potato air means three consecutive days of MEP’s API above 200 (including a 2/20 peak of 333 – equivalent to a daily average PM10 concentration of 446 ug/m3), the US Embassy’s BeijingAir Twitter feed consistently reading “Hazardous” or “Beyond Index” (PM2.5 concentrations peaking above 500 ug/m3), and the China National Environmental Monitoring Center’s new hourly air quality data showing…well, no particulate matter data at all for at least the past 48 hours for most centrally-located stations. This is disheartening, because it’s extreme episodes like this during which people – especially at-risk populations – need that data the most. The Wanshouxiguan (万寿西官) station does have hourly PM10 data, which show a peak near 480 ug/m3 (graph below shows that station’s hourly PM10 data from 2/21 6pm to 2/23 6pm):

For context, remember that the WHO’s daily recommended PM10 limit is 50 ug/m3, while the annual limit is 20 ug/m3.

Unfortunately, I have no time this week to run additional data analysis or provide more lengthy commentary, though I would like to repeat my previous comment about the Beijing EPB’s claims of credit for January’s excellent air quality: “If January’s good air quality was ‘far from a one-off,’ does this mean we can expect this much improved air quality to continue? (If it doesn’t, then I will be very curious to see what explanation is offered (if any) when the air pollution levels go back up to more expected levels for this time of year.)” The Beijing EPB issues monthly air quality summaries on the last day of each month, so let’s see what they say next Monday.

Lastly, just one criticism of the AFP story that’s going around:

BEIJING — Thick smog blanketing Beijing went “beyond” measurable pollution levels on Monday, the US embassy said, as a Chinese official warned people to stay indoors and avoid outdoor activities.

Actually, the pollution levels are still measurable, and reported. You can still see the pollution level, as highlighted here (in this case, a PM2.5 concentration of 515.0 ug/m3):

“Beyond index” doesn’t mean the pollution can’t be measured, it just means that the pollution level is beyond the US’ standard system for categorizing, which maxes out at 500. (Though we all know what it’s really called.)

Great news! Today is Beijing’s 36th consecutive Blue Sky Day, a day whose Air Pollution Index (API) is 100 or below, indicating “excellent” or “good” air quality. As far as I can tell, this is the longest consecutive streak of Blue Sky Days in Beijing for at least ten years. Previously, there were only three streaks of 30 days or longer, one in 2006 and two during the Olympics.

Although we have seen gaming of the Blue Sky Day metric in the past, in this case both the data and public observation support dramatically cleaner air quality over January 2011 than in months and years past.

On the data side, for the 36-day period December 23, 2010 to January 27, 2011, I calculated an average particulate matter concentration of around 64 ug/m3 in Beijing. (API to PM10 concentration methodology here.) While this is still well above the WHO’s recommended annual limit of 20 ug/m3, this pollution level is less than half of that over the same period in 2009-2010, and is actually on par with the pollution levels during the Olympic (57 ug/m3) and Paralympic (71 ug/m3) periods, which were widely regarded as successful.

Looking at the data another way, an astonishing 18 of the past 36 days have been Grade I “excellent” air quality days in Beijing, which means the API is 50 or below. In 2001, Beijing only had 12 Grade I air quality days the entire year.

From a public observation perspective, I offer up for evidence the conversation I mentioned in my last post which made me start thinking about the streak, this e-mail I received two days ago from another friend:

I’ve been meaning to ask but since pretty much Christmas Eve I feel like has been the best stretch of air quality since I landed here…even better than the Olympics (which I caught the tail end of). My general air quality test is how well I can see the mountains from Tsinghua or Andingmen bridge. Rarely has there been a m