Is Air Pollution a Problem in Mongolia?

Air pollution or grasslands – which is more likely to come to mind when you think of Mongolia? Air purifiers and air pollution masks certainly aren’t top on the packing list when people are heading off to Mongolia, but should they? According to The Guardian, Ulaan Bator is the world’s … Read more

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: I … Read more

Can DIY Air Purifiers Clean Large Rooms?

Can DIY air purifiers clean large rooms? Hundreds of hours of Smart Air tests have found that DIY air purifiers cut fine particulate, reduce smoke, remain effective over 200 days, and even capture chemicals like formaldehyde. But an important practical question is whether DIY purifiers are effective enough to purify large rooms.

DIY Air Purifier Search

To answer this question, I tested every fan I could find, as long as it had a flat front. I was looking for a fan that put out a lot of air.

After getting all the data, of one fan stood out above the rest. I called it “the Cannon.”

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. I wanted to know how well a DIY air purifier can clean under real-world conditions.

DIY Air Purifiers Clean Large Rooms: The Test

I tested the Cannon on its high setting six times in a 30.5m2 living room–a large, open space. To track pollution, I measured 0.5 and 2.5 micron particles using a Dylos laser particle counter. Each test lasted at least three hours.

DIY Air Purifiers Clean Large Rooms Test Setup

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

DIY Air Purifier Clean Large Rooms Test Cannon

Besides testing in a big space, this experiment extends the findings 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–PM2.5 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.

DIY Air Purifiers Clean Large Rooms Effectively

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.

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.

Bottom Line:

With a fan as strong as the Cannon, DIY air purifiers clean large rooms effectively, reducing 0.5 micron particles 92% on average.

Smart Air

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

 

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Chinese New Year fireworks pollution

Do Chinese New Year Fireworks Pollute Indoor 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 … Read more

PM2.5 Particle Size Virus

The Really Small Stuff

An open-data DIY air purifier test found that even simple, homemade purifiers can reduce particulate, but can they capture the smallest particles? This question is important because it’s the smallest particles that can penetrate deep into our lungs and even enter our bloodstream. To test how effective the DIY purifier … Read more

How Safe Is Indoor Air?

I recently did some research on whether indoor air is as bad as outdoor air. Before that, I had a conversation with a friend 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.

 

The Test

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:

1indoor

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: Indoor air is relatively safer

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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Comparing Air Purifiers

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

DIY Purifier Tests

How do I know if a DIY purifier works? I think you can break this down into two questions: Is the air coming out of the DIY purifier clean? The test results are as clear as can be. The DIY purifier shoots out very clean air. But is that enough to actually … Read more

How to Make a DIY Air Purifier

How can we make a homemade DIY air purifier?  Air purifiers can be extremely expensive.  But they don’t need to be. After researching how different air filters work, I concluded that a HEPA filter is all that’s needed to make an effective air purifier. Given that most air purifiers sell … Read more

Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.