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Winter (Air) is Coming

Another year, another Beijing winter. As winter arrives to Beijing, I got to wondering: how much worse is winter air?

To get to the bottom of it, I analyzed the last seven years of US Embassy PM 2.5 data. I found that the capital’s air has averaged 111 micrograms in the winter versus 92 micrograms for the rest of the year.

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Just how bad is that? The WHO 24-hour PM 2.5 limit is 25 micrograms. That means Beijing’s summers average three times the limit, and winters average over four times limit.

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Breathe safe this winter!

 

indoor vs outdoor

Shanghai Test: Is Indoor air better than outdoor air?

When I got my very first particle counter, I tested sites around Beijing to see whether indoor air was better than outdoor air. It was.

But that test had some limitations. My first particle counter didn’t have a battery, so I had to estimate outdoor particulate in some locations. I also didn’t look into any variables that could give some indoor locations better air than others.

Shanghai Test

Now I’ve got a fancy new Dylos DC1700 battery-power particle counter! Now I can easily take measurements indoors and outdoors. Here’s what it looks like:

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I took it to Shanghai and tested 14 times in 11 locations on August 27-29. While I was there, the AQI averaged 158 (70 micrograms). I tested mostly around the French Concession, although I also made it out to Fudan University. None of the locations use air purifiers.

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I tested in any type of place I could, and I mean any place. Here’s what I recorded in a public bathroom stall:

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Results

I focused on the smaller 0.5 micron particles (which are highly correlated with government PM 2.5 readings). Across the 14 samples, here’s what I found. The red line represents how many particles were in outdoor air.

http://smartairfilters.com/cn/

On average, indoor air had just 69% of the particles of outdoor air.

Why do some places have cleaner air?

This fits with my findings in Beijing–indoor air has less particulate than outdoor air. But next I wanted to see if I could figure out why some places had cleaner air than others. For example, my unpurified apartment air (unpurified because I just got home) had just 30% of particles compared to outdoors, but the public bathroom had 134% of particles compared to outdoors. Woah!

I tested the simplest explanation possible: Were the windows and doors open? Most particulate pollution comes from outside. And in closed rooms, particles will slowly fall to the ground. Thus, indoor air should be better when the windows are doors are closed.

To test that idea, I looked only at places that had doors or windows open:

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Yikes! If the doors or windows are open, I was breathing air that was basically as bad as outdoor air (92%). For example, here was how air compared indoors and outdoors in the public bathroom:

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But things were much better in places with the doors and windows closed:l

With the doors and windows closed, the air had 57% of the particles of outdoors. For example, here’s the air inside Fudan University’s Economics Institute versus outdoors:z

In places where the doors and windows were closed, the air was always better than outside. The one exception was the Yuanyuan Restaurant, at 115%. Those particles could be coming from the kitchen.

So what?

The conclusion here is simple: We’re usually breathing much less particulate indoors than outdoors–even without a purifier.

Clean Lung Tips

  1. Work out indoors if possible. I work out indoors in a gym rather than outdoors when I’m in China.
  2. Sit inside at cafes or bars (unless people are smoking).

Does that mean indoor air is safe?

Indoor air has less particulate, but remember that “less particulate” does not always mean “safe.” Out of all 14 tests, NONE of the numbers was below the WHO 24-hour PM 2.5 limit:

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One Last Exception

Finally, remember that pollutants can sometimes come from indoors. This is usually from the paints and chemicals used in remodeling and new furniture. If your home smells like paint or new furniture, you may be safer opening the windows (or at least using activated carbon).

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Is Air Pollution a Problem in Mongolia?

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According to The Guardian, Ulaan Bator is the world’s second most polluted mega city. From 2008-2011, the average PM 2.5 level was nearly 150 micrograms. In 2014, Beijing averaged 98 micrograms; the WHO 24-hour limit is 25 micrograms.

 

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Is it a bustling manufacturing sector? Manufacturing is still a tiny percentage of the Mongolian economy. Cars filling the streets? Not that either.

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It turns out, most of Ulaan Baatar’s pollution is from people burning coal to keep warm. A little heat is necessary where winter temperatures dip to -40 C.

Yet all that air pollution causes 1 in every 10 deaths in the capital, according to an academic study. That makes clean air an urgent need in this city of 1.2 million people.

Smart Air will host its first-ever Mongolia workshops in Ulaan Baatar! Join us in the Mongolian capital September 11th and 12th.

Join us to learn how DIY purifiers can help remove dangerous particulate pollution from inside the home. Smart Air founder Thomas Talhelm will explain how even the priciest purifiers use a fan to push air through a HEPA filter. Workshop participants will make their own in just 10 minutes, and they’ll take it home to start breathing easier right away.

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What time of day is PM 2.5 the lowest?

My intuition has always been that air pollution is lowest at night because there are fewer cars on the road and fewer factories humming. Apparently I’m not alone: 139 voted for their guess about what time of day has the lowest PM 2.5, and night time came in first:

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I also know people who arrange their schedules to work out in the morning to avoid the worst pollution. But how accurate are our intuitions?

To get to the bottom of it, I analyzed thousands of hours of PM 2.5 data from the US Embassy in Beijing. When I finally got the answer, I was surprised:

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Instead of during the quiet of night, it’s the afternoon–right around rush hour–that PM 2.5 is the lowest. So if you’re planning a picnic or insist on exercising outside, you’re usually best off between noon and 6pm.

What about other cities?

Is that how PM 2.5 generally works, or is it unique to Beijing’s activity or climate? Fortunately, US consulates in several other cities publish their historical data.

Shenyang

In terms of climate, Shenyang is pretty similar to Beijing, and its daily PM 2.5 patterns are very similar (although night time isn’t quite as bad as Beijing):

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Chengdu

The pattern in Chengdu is similar. PM 2.5 is lowest in the afternoon and highest in the morning.

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Shanghai

The picture starts changing when you get to the south. In Shanghai, PM 2.5 is lowest in the afternoon (like the north), but there’s also a dip in the very early morning:

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Guangzhou

Guangzhou’s pattern was virtually identical to Shanghai’s: a dip in the very early morning and a dip in the afternoon.

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Bottom Line: When is it safest to be outside?

In all five cities, the afternoon had the lowest PM 2.5 levels. And in contrast to many people’s intuition, the night time had the worst air in several cities. Thus, you’re usually best off organizing your picnic or tai chi in the afternoon.

But keep in mind that the air is NEVER safe on average in any of the five cities at any time of day. So take “safest” with a grain of salt!

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Open Data

All of the data is available from the US embassy and consulate websites. Thanks to Josh Malina for collecting and analyzing the consulate data.

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How Big of a Room Can the Cannon Clean?

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After I tested every fan in China I could find with a flat front…

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…the results of one fan stood out above the rest. Because of its appearance and how much butt it kicked, I called it “the Cannon.”

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In Anna’s 15m2 Beijing bedroom, it crushed particulates. It removed 97% of the small .5 microns particles.

But how well can it do in larger rooms? Most companies estimate this using flow rate, but those calculations depend on how well houses are sealed and how dirty the air outside is. Since air outside is dirtier in China, I think it’s necessary to do real-world tests.

Methods

Fortunately, I moved into a large 4-bedroom apartment, with a 30.5m2 living room. I tested the Cannon six times on high and tracked particulates with a Dylos particle counter. Each test lasted at least three hours.

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I calculated the percentage reduction in particles from the first hour to the last hour.

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This test also serves as an important extension of the earlier room tests because:

  1. These tests were run in the daytime. Several people have the intuition that pollution goes down at night because people are less active and fewer cars are on the road (but the data shows that intuition is false–PM 2.5 pollution is worst in the middle of the night in Beijing).
  2. These tests were run while people were moving around in the room and opening the door to the outside. This is more conservative than the nighttime tests because the Cannon has to fight influxes of outdoor air.

Results

Over six tests, the Cannon removed 92% of .5 micron particles and 89% of 2.5 micron particles even with people moving around and opening doors.

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In previous tests, 2.5 micron reductions were usually slightly larger than .5 micron reductions, so it’s a little surprising that the 2.5 micron reduction was 3% lower than the .5 micron reduction. My guess is that this is because people were moving in the room, and human movement affects the 2.5 micron readings much more than the .5 micron readings.

Conclusion

The Cannon can clean rooms at least 30.5 m2, which puts it above the 22.3 m2 Blue Air recommends for their 3,6000 RMB 203 model.

As always, I’m posting the raw data and more details on the methods for fellow nerds below.

 

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Does Chinese New Year Affect Inside Air?

I’ve posted data before showing that outdoor air quality is strongly correlated with indoor particle counts (r = .71), but Chinese New Year gives nerds like me a great chance to see what happens when we get a momentary shock to air quality.

The media made a big deal about people cutting back on fireworks this year out of a concern for air quality, and that may be true, but you can still see a strong spike in PM 2.5 as Beijingers rang in the year of the horse:

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Not all that surprising. But what’s more interesting is that you can see a corresponding increase in the particle counts in my collaborator Gus’s bedroom (blue line):

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These indoor counts are without a purifier running, so they demonstrate how quickly outdoor air pollution can find its way indoors and how variable indoor air quality can be in a single room over time. Simply put: the worse the air is outside, the worse it is inside.

Yet the glass half empty can also be half full. When outdoor particulate goes down, indoor particulate can go down in a hurry. Check out what happened after the firework apocalypse ended:

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A note for fellow nerds: The indoor particle counts are not precisely on the hours, so the apparent time lag between indoor and outdoor counts may be exaggerated.

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How Safe is Indoor Air?

I recently had a conversation in Beijing that went something like this:

Friend: I’m not sure if I can make badminton tomorrow. I have a basketball game in the day.

Me: Oh man, do you play outside?

Friend: Nah, it’s inside.

Me: Oh, phew. Good.

Friend: Wait, why do you say that?

Me: Oh, the air is way worse outside. I used to feel like I had asthma after playing basketball outside.

Friend: Really? No, they’re not that much different. I saw it’s just 20% different.

Seeing as how nerds cannot let matters of fact go, I started using my particle counter to take measurements of inside and outside air at different locations around Beijing. This answer is important: it tells you if it’s any safer to exercise indoors and how much damage you’re doing to your lungs by choosing that seat outdoors at your favorite cafe or restaurant.

So I took measurements in six locations around Beijing, in apartments, cafes, and my gym. I only chose bad days (pollution concentration above the WHO standard of 25), and I avoided days where it rained (because rain can cause quick changes in air quality). Here’s what I found:

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On average, indoor air had only 36% of the pollution outdoors.

Things were a little worse for the smaller .5 micron particles, but still much better than outside:

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On average, indoor air had only 51% of the .5 micron particulates of outside air. My guess is that the .5 micron data was worse than 2.5 micron data because it’s easier for smaller particles to get into your home and stay suspended in the air.

There is a lot of variation between places. For the 2.5 micron particles, the locations varied from 14% to 58%. Dr. Saint Cyr also found significant variation between two apartments he lived in, 50% to 70%.

Conclusion: In terms of particulate pollution, you’re safer snagging an indoor seat and working out indoors, particularly on bad days (I’ve seen some argue that we are particularly vulnerable when we work out because we breathe more deeply than normal).

But remember that doesn’t mean indoor air is safe, just better than outside. For example, if your air at home had 40% of Beijing’s concentration last night at 11pm (8/15), you would’ve had 64 g/m3 in your home, which is more than twice the WHO standard of 25.

As usual, I’m posting more on my methods and raw data below.

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More Comparisons

Dr. Saint Cyr recently pointed me to great tests of air purifiers from the Shanghai Consumer Protection Bureau:

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The reason this type of research is so badly needed is that Western research (like this report from Consumer Reports) focuses on allergens, not general industrial air pollution. Allergens are probably more relevant for most Americans, but for those of us living in China, particulate air pollution is the real problem. And a lot of smog is smaller than pollen:

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Thus, I was excited to see research that focused on PM 2.5 here in China (results here, in Chinese). In removing PM 2.5, 17 out of 22 models removed more than 90% of PM 2.5 in just 20 minutes in a 30-square-meter room. Pretty good!

Yet even the cheapest of the “non-famous” brands cost about 1,500 RMB. For that price, you could make 9 of my DIY filters, and that’s before eating the cost of proprietary replacement filters (US$200 a piece at IQ Air). Even with these cheaper brands, I still think consumers lack a truly affordable way to get clean air. Using the consumer bureau’s results, I calculated how much you’re paying for each percent reduction in PM 2.5.

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Now, their tests weren’t perfect. The biggest downside I see is that they used cigarette smoke as the PM 2.5 source, rather than outside air. It’s not clear to me if cigarette smoke behaves the same as smog in filters. Also, many filters were less effective at removing the formaldehyde that they released in the room. That said, I don’t know how much formaldehyde is in the air normally.

But these results from Dr. Saint Cyr do use ambient air pollution in China (as do mine 1, 2). In tests with doors closed and the filters at their highest settings, Dr. Saint Cyr’s two Alen Air filters, Blueair, and IQ Air all got rid of at least 95% of PM .3. But the Alen Air A375 will set you back US$500 or RMB 5,000 imported in China. Here’s how to get the same results for 166 RMB.

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Purifier Tests

I think you can break the question of whether an air purifier works down into two questions.

  1. Is the air coming out of the purifier clean? This is the easier question to answer, and the test results are as clear as can be. The DIY purifier shoots out very clean air.
  2. But is that enough to actually clean the ambient room air? For example, if you have a really tiny filter and a huge room, the filter could work properly but still not be strong enough to make a difference.

Answering this question is more difficult because you need a controlled environment (you can’t open and close windows during the test), and you need to test the air for a longer period of time. Fortunately for you, I’m a nerd, and I’ve been doing these tests for fun for the past few weeks.

 

According to my particle counter, here’s what the filter did in an hour:

 

I’ve also tested the effect by running tests with the particle counter on hourly mode. These tests show that the downtrend continues over several hours:

 

(Note that the hourly test and minute test are on different days.)

The particle counter also gives data on 0.5 microns – even smaller particles. Here’s what that looks like over eight hours:

 

Conclusion: The DIY purifier works. You can get clean air for 166 RMB, as opposed to 8,000 RMB as long as you know that a HEPA filter is all you really need to fight particulate air pollution in China.

From my perspective, filter companies like IQ Air are taking advantage of how little we know about air pollution and the fact that you need expert instruments to tell whether the filter is working or not. When consumers don’t know how to assess the products we buy, we often use price to tell us whether the product is good. That happens with expensive wines all the time. I’m convinced you can breathe safe air in China for far less than filter companies want you to believe.

Finally, for data nerds like me, I’m including more details on the tests here:

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Test details:

The test above was done starting at 11:30 pm (I’m a night owl) on 6/16/2013, when the outside AQI in Beijing was 230 according to the US embassy’s AQI Twitter feed. (The outside air improved the next day, but results were similar on a later test where AQI actually went up slightly from 195 to 202 during the test. Details to follow here.)

According to comparisons of my particle counter’s tests of outside to US embassy AQIs, an AQI of 230 would convert to about 2,650 on the 2.5 micron count on my reader. (Remember, the particle counter gives the raw number of particles 2.5 micrometers and above per .01 cubic feet. The US embassy takes mg/m3 and converts that to an AQI. Therefore, the numbers are different, although they correlate.)

I did the test in my bedroom with the doors and windows closed. The room is 13.5 meters squared, with two windows.

Astute readers have asked whether I let the particle counter run a bit to get a stable reading before turning on the filter. The particle counter tends to take a 5-10 minutes to get stable readings. To be conservative, I gave it about an hour:

 

(Update: This question is answered with much more data in my new tests where I left the particle counter on for 6 days, and I turned the DIY Cannon on a timer to turn on every day for 2 hours.)

The spike at the top was when I entered the room to turn the air purifier on and reset the machine, so it may just be noise or it may be the dust I kicked up by walking around. A more stable reading for that time would probably be about 230.

The uptrend prior to turning the filter on may have been because I was running my dehumidifier prior to the tests, and I have some small filters in that. (Yes, for some reason my house gets very humid–at times over 80%–despite the fact that Beijing is a semi-desert. I think it’s a problem with the plumbing system.)

Regardless, this data suggests that the effect of the filter was NOT a confound of calibration.