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。

1-9

大炮能够净化多大的房间?

我测试所有能找到平面的风扇之后,

2

……当中一台最突出。因为它独特的样子和它非常好的效果,我决定叫它“大炮”。

3

在15m2的北京公寓,大炮大量地消除了颗粒,连很小的0.5微米颗粒也降低97%

但是在更大的房间内,效果怎么样?一般大的公司会用风量来算适用面积,但是这种算法会受到房子密封性和外面空气的污染程度的影响。因为中国的空气更脏,我觉得有必要在真实条件下做测试。

方法

幸亏我搬到大的四居室公寓,包括30.5m2的客厅。在这个客厅,我做了6次大炮高档测试。我用了激光测试仪来测试颗粒污染。每次测试持续了至少3个小时。

4

我算了大炮从测试开始到最后一个小时消除百分之多少颗粒。

5

这次测试跟之前做的测试有比较重要的区别:

  1. 这些测试是白天做的。很多人觉得PM 2.5是晚上最低,因为开车的人少(不过这个想法是错的,数据显示PM 2.5是晚上最高)。
  2. 这些测试是在人走动和开门的时候做的。这个比睡觉的时候的测试更保守,因为大炮要克服开门进来的脏空气。

结果

通过6次测试,即使有人走动和开门,大炮消除了92%的0.5微米颗粒和89%的2.5微米颗粒。

6

这次测试有一个小意外:0.5微米的效果稍微比2.5微米效果要高。在之前做的测试,一般0.5微米的效果会低一点。我猜这是因为测试的时候有人走动,而走动对大颗粒的影响更大。

结论

大炮至少净化30.5m2的房间。这个比 3,6000元的Blue Air 203适用面积(22.3m2)要大。

跟之前一样,为了其他书呆子同胞们,我在贴子下面发布原始数据。

(更多…)

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Does Chinese New Year Affect Inside Air?

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.

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:

1

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):

2

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:

3

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.

2015061632121471

How Safe is Indoor Air?

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.

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:

1

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:

2

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.

(更多…)

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More Comparisons

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.

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

1

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:

2

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.

3

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.

compare-original

Purifier Tests

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.

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:

more

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.