6

寒冬(的雾霾)将至

又一次冬天,又来一次PM 2.5来袭!面临北京冬天的PM 2.5,我开始想:冬天PM 2.5到底比夏天差多少?

我分析了北京美国大使馆近7年的PM 2.5数据,结果夏天平均PM 2.5为92微克,冬天为111微克。

a

这有多严重?世界卫生组织PM 2.5的24小时上限是25微克。那么北京夏天平均PM 2.5是上限的三倍多,冬天是四倍多。

b

寒冬将至,做好准备!

indoor vs outdoor

上海测试:室内比室外空气好吗?

我刚拿到第一台空气测试仪的时候,我做了一个小测试:我去了北京几个地方采样,想看看室内空气是不是比室外空气好。结果发现是

不过,那次测试有些缺点。首先,我第一台测试仪没有电池,所以我当时只能估计外面的空气污染。第二,我当时也没分析有什么因素让某些地方的空气比其它地方要好。

上海测试

现在有了很方便带电池的Dylos DC1700测试仪!可以测到室内和室外的空气。这是我最近在上海测到的空气:

图片 1

我趁去上海的机会做了新的研究:我在8月27-29号在11个地点做了14次测试,测试了室内和室外的空气。那几天上海AQI平均为158 (70微克)。我主要是在法租界采样,另外去了复旦大学。所有的采样点都不用空气净化器。

图片 2

我尽量去更多地方做测试,连公共厕所都进行测试了:

图片 3

结果

我分析了0.5微米颗粒(上面的图片左手边的数值);这些小颗粒跟政府的PM 2.5数值相关性很高。14次测试的结果是这样的,红色线是外面的污染程度:

 

图片 4

平均来说,室内的空气污染只有外面的69%。这个结果符合我在北京做的测试结果,也符合美国环保局的测试结果

为什么有的地方空气更好?

后来我想知道为什么有的地方的空气更好,有的地方更脏。比如说,我回家的时候(还没开净化器),我家里只有外面空气的30%的颗粒!但是我去的公厕有134%的颗粒–比外面还要糟糕。

我分析了最简单的原因:门窗关着还是开着?颗粒污染主要来源是外面的空气。而且,如果关门窗,颗粒会慢慢下降而落在地上。所以关门窗的时候,室内的空气应该更好。

所以我先分析了所有开着门窗的地方:

图片 5

很恐怖!如果开门窗,我呼吸的空气基本上跟外面一样脏(92%)。下面的图是公厕的实拍:

图片 6

不过,在平时关门窗的地方,结果很不一样:

图片 7

关门窗的地方只有外面的57%的颗粒。下面的图是在复旦大学的实拍:

图片 8

还有,关门窗的地方的空气总是比外面要好。只有一个例外:圆圆餐厅有(115%)。这些颗粒物应该是来自炒菜。

结论

结论很简单:我们一般在室内呼吸的空气比外面的要好,就算不用空气净化器。

建议

  1. 尽可能在室内运动。我在中国的时候在健身房锻炼身体(我在外面的时候戴口罩)。
  2. 在咖啡厅和酒吧,我一般选择坐在里面而不是外面。

最后一个例外

值得记住:有时候空气污染来自室内。一般这种情况是因为刷墙或者装修。如果家里有那种装修的味道,有时候开门窗更好(或者用活性炭)。

这意味着室内空气安全吗?

我说室内空气比外面好,但是要记住:“更好”不等于“安全”。14次测试当中,没有任何地方低于世界卫生组织的安全上限:

图片 9

2

蒙古有空气污染吗?

图片 1

据英国《卫报》, 乌兰巴托是世界大都市空气污染最严重第二。 2008-2011年,乌兰巴托PM 2.5平均值接近150微克;北京2014年平均PM 2.5是98微克;世界卫生组织24小时上限是25微克。

2

是快速发展的工业生产的原因吗?工业化的工厂只占蒙古经济极小的部分。满街都是汽车尾气?也不是。

3

实际上,乌兰巴托大部分的空气污染来源是冬天供暖烧煤。在冬天温度达到零下40度的地方确实需要供暖。

研究者发现那么严重的空气污染导致首都人口有10%的早逝。这意味着乌兰巴托急需清洁空气的好办法。

Smart Air将在乌兰巴托举办首场蒙古DIY空气净化器沙龙!欢迎蒙古首都朋友们在9月11-12日加入我们洁净空气活动。

欢迎加入我们DIY沙龙,了解如何用简单的DIY空气净化器减少家里的有害颗粒污染。Smart Air创始人Thomas Talhelm将解释非常贵的空气净化器的工作原理及如何利用同样的道理保护自己和保护自己的钱包。参加者在现场制作自己的DIY空气净化器带回家。

2-6

一天中什么时候PM 2.5最低?

我在中国待的时候,我一直猜空气污染晚上最低,因为汽车少,而且工厂活动也少一点。好像我不是唯一一个人这么想:139个人投票自己的猜想,结果猜的最多的是夜间。

14

我还认识几个人,为了避免污染最恶劣的时段,特意在早上锻炼身体。那我们的直觉到底准不准?

为了水落石出,我分析了来自美国大使馆的几千个小时的PM 2.5数据。看结果的时候,我很惊讶:

8

夜间并不是PM2.5最低的时间段,反而是PM2.5最高的时间段!其实是下午(差不多交通高峰时)PM 2.5最低。所以如果在安排野餐或者一定在室外锻炼身体,平均最好是中午和18点之间最好。

其它城市呢?

这是PM 2.5的普遍趋势,还是北京的气候或者其它的特点?幸亏其它的美国领事馆发布历史数据。

沈阳

沈阳的气候跟北京差不太多,而且PM 2.5的趋势很像(不过,沈阳夜间没有北京那么恶劣)。

9

成都

成都的趋势很像:PM 2.5一般下午最低,早上最高。

10

上海

开始往南走,趋势就变了。在上海,PM 2.5最低有两个时间段:下午(像北京)和凌晨。

11

广州

广州的趋势很像上海的:PM 2.5凌晨的时候还有下午最低:

12

结论:最好什么时候安排室外活动?

数据显示很多人的直觉(包括我自己)是错的:PM 2.5在夜间的时候最高(上海除外)。在五个城市,PM 2.5是下午最低。所以如果要安排野餐或者室外活动,一般来说最好安排在下午或者凌晨。

不过,也要注意:这几个城市所有的平均值当中,没有任何数据算是安全的空气:

13

公开数据

文章所有的数据是公开的,来自美国大使馆领事馆的网站。感谢Josh Malina帮忙收集和分析领事馆的数据。

1-12

广州的空气安全吗?

1

北京的空气污染是中国最出名的,但是这个会让一些其它城市的人觉得自己的空气还好,至少比北京好。实际上,其它城市的空气安全吗?

2013年上海人遇到雾霾,很多上海人发现自己的空气也不安全。但是广州呢?广州的空气安全吗?

为了回答这个问题,我分析了美国领事馆的2014年每个小时的数据。迄今4,572次数据。然后我算了有百分之多少次超过世界卫生组织的PM 2.5上限(25微克)。

看了结果之前,猜一猜百分之多少超过安全限:

  1. 10%
  2. 25%
  3. 50%
  4. 75%
  5. 90%

答案在下面

2

2014年,迄今 有76.9%的数据次数超过WHO的上限。平均的PM2.5数值是53.4微克–WHO上限的两倍。

Breathe safe, Guangzhou!

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A New Way to Test Whether the DIY Works

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

So far, I’ve been testing air purifiers by taking a baseline measurement of particulate pollution in a room, and then turning on the purifier and testing whether the counts drop. I’ve used that method to test the DIY and more expensive machines.

However, I recently bought a second particle counter, so my collaborator Gus suggested another method: run one particle counter in the bedroom that has the purifier, and run another particle counter in a different room that does NOT have a purifier. The benefit of this method is that the control room represents the counterfactual–what would have happened if we hadn’t turned on the air purifier.

Thus, if a northwest wind hits Beijing and makes the outdoor air a lot cleaner, we can separate the effect of the outdoor air fluctuations from the effect of the purifier. In that situation, my old method would artificially raise our estimates of effectiveness. Changes in outdoor air can also artificially lower our estimates of effectiveness if the outdoor air gets dirtier after we turn on the purifier.

In previous tests, I corrected for this by averaging over multiple tests. I also analyzed the data after removing days in which outdoor air pollution fluctuated a lot (for example, I do that sort of analysis in the extra nerd notes here).

But it’s always nice to use different types of tests to make sure an effect is real, so Gus did this experiment. He set up one particle counter in his room and one in his kitchen: 1

He let the particle counters run for several hours, and then a timer turned on the Original DIY in his room. (The kitchen had no air purifier.) Here’s what happened:

2

The difference between the bedroom and the kitchen air quality can approximate the effect of the air purifier. It looks like Gus would have been breathing 16,000 of these 0.5 micron particles in the air in his bedroom if he hadn’t turned on his DIY purifier.

And it’s pretty clear that the kitchen air quality (where we don’t have a purifier running) is following outdoor air quality:

3

(Be aware that I’m overlaying these two lines on the same graph, but the Y-axes are different. This is NOT saying that indoor air is as bad as outdoor air. Indoor air is usually cleaner than outdoor air.)

Conclusion: Similar to earlier tests, the double particle counter test shows that the DIY purifier is removing particulate pollution from the air.

As always, I’m including more details for fellow data nerds below.

more

What about the 2.5 micron particles? In the main text, I present the 0.5 micron results, but what about the larger particles? The results there are similar:

4

Remember that because these particles are larger, they are more affected by people moving around. That’s probably why there are large spikes from 7 to 9pm, and why counts level off after midnight. However, even after the numbers level off, the purifier is reducing the counts in bedroom even further.

Timing: Careful readers will notice a slight lag between the bedroom and kitchen numbers. That’s because after entering its hourly mode, the Dylos particle counter takes its first measurement after a random number of minutes. (After that, it’s every 60 minutes.)

Therefore, we cannot guarantee the kitchen and bedroom numbers are taken at the exact same time. However, after the fact, we can tell when the measurements were taken. Thus, we know that the bedroom numbers were taken at 27 minutes past every hour, and the kitchen numbers were taken at 36 minutes past the hour. Those numbers are reflected on the X-axis.

Percentage effectiveness: I also computed the percentage reductions in particulates using my regular method of averaging the last four hours before the DIY was turned off. Then I compared that as a percentage of particulate in the kitchen.

According to that calculation, the DIY removed 86% of 2.5 micron particles and 87% of 0.5 micron particles. Compare that to 92% of 2.5 micron particles and 84% of 0.5 micron particles in my earlier tests. However, I am cautious about drawing strong conclusions from one day’s data. It would be best to average the results of several testing days.

3-27-1024x728

More Data!

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

A while back, I posted data comparing how effective the DIY purifier was compared to a 6,000 RMB Blue Air and 11,000 RMB IQ Air. In that test, I calculated effectiveness as percent difference from outside air. At the time, I said I didn’t like that way of calculating effectiveness, but I did it that way so I could compare my results with the results of Dr. Saint Cyr.

Now I’m posting data from new tests that improve on the old tests in three ways:

  1. The new tests calculate effectiveness as the percentage reduction from indoor air. This gives smaller percentages because outside air is dirtier than inside air. In my opinion, this is a more rigorous way to test air purifier effectiveness.
  2. The new tests were conducted by my Smart Air collaborator Anna Guo in her apartment. This helps test whether the results are generalizable. In other words, this way we can know that my original results were not a fluke just based on the layout of my room or how well my windows are sealed. Anna’s room (15 m2) is also slightly larger than mine (13.5 m2).
  3. Finally, the new tests are with the Meidi fan I’m now shipping to people from my Smart Air site. Thus, these results are more relevant for people using our DIY filter kits. (However, the Meidi fans are very similar to the blue Kadeer fans I was using before. I haven’t seen a noticeable difference in the results with the two fans.)

Methods: Anna used my particle counter to take a baseline 2.5 micron reading before turning on the filter. Then she turned on the filter, put the particle counter on the other side of the room from the DIY purifier, set it to take hourly measurements, and went to bed.

To calculate effectiveness, we took the average 2.5 micron reading of the four hours prior to waking up and calculated the percent reduction from the baseline reading before turning the filter on.

Filter: We used the same DIY kit with the Meidi fan that we’re shipping from Smart Air:

1

Results: Here’s what the data looks like. This data is from September 9th:

2

In these real-world tests, we need to be careful to check that outdoor particulate didn’t go down during the test. If it did, we would think the decrease is due to the purifier when really it’s due to outdoor air changes. To test that, we can overlay the outdoor PM 2.5 readings from the US Embassy:

3

Outdoor air actually got slightly worse during the test, so the reduction inside is not because outdoor air got cleaner.

And here’s the average reduction in 2.5 micron particles over the three test nights:

4

Conclusion: The DIY filter removed an average of 92%. That’s similar to the earlier result of 94%. I suspect the new result is 2% lower than before because this new calculation uses reduction from inside air rather than outside air.

Again, the effectiveness ratings are similar to Dr. Saint Cyr’s tests with the Blue Air and IQ Air, although remember that his room is larger (20 m2), and the post does not specify the length of testing time or the particle counter used. Ideally we’d have tests with the same particle counter in the same room.

As always, I’m posting more details on the methods for fellow nerds here:

(更多…)

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The Limits to Counting Particles

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

If Particle Counting has just one take-home message, it is that you can protect your yourself from particulate pollution in China, and it costs a lot less than filter companies want you to think. However, I don’t want to mislead people into thinking that turning on a filter will definitely solve any possible problem. I talked with Louie Cheng, who founded Pure Living China, a company that tests for pollutants in homes and offices, and we came to a few conclusions about the limits of filters:

  1. Particulates are not everything. 

Particulate pollution is a big deal in China, and it’s bad for your health. There are lots of studies out there showing this, but the one that pops into my head the most is the study showing babies exposed to more air pollution are born with smaller heads. If that’s not scary, I don’t know what is.

However, particulates are not everything. Gas pollutants can be a problem too. Although I suspect that almost every home in China has particulate pollution while only some have gas pollution, there are dangerous gases out there like radon, carbon monoxide, and the broad category of “volatile organic compounds.” Unfortunately, even the fancy filters have trouble consistently capturing a wide range of gases.

If you’re considered about gases, consider getting a home test from Pure Living China. They’re not cheap, but I’d consider it if I had unexplained health problems or a child at home.

I try to write “particulate pollution” rather than “pollution” because not all pollutants are particulates. However, it’s easy to just covert “particulate pollution” to “pollution” in our minds.

  1. Some particles are too small for filters.

A quick look at the size of different particles and gases makes it clear that particulate filters can’t get everything:

1

HEPAs are rated to .3 microns (micrometers), and I’ve seen reports that they can get particles of .1 microns, but there are still leftovers. For example viruses and gases will pass through air filters (but not bacteria). (This, by the way, explains what I call “the smoker paradox.” More on that later.)

  1. Opening your window is good (sometimes). 

The air outside in China is scary, but sometimes it is actually good to open your windows. That is because some pollutants can come from inside. Some common sources are formaldehyde used in some furniture, cooking without a good vent, and construction work.

In those cases, it can actually be a good thing to open your window, particularly on blue sky days.

Conclusion: Air purifiers will get a lot of pollutants out of your air, but there are limits to what you can filter out. Consider opening your windows on clean days–and particularly if you have renovation going on indoors or are cooking without an adequate vent.

Thank you to Louie Cheng for sharing his expertise.