Geek-Out on Clean Air

Update: Nov 8, 2019

Tracking Air Quality in your Region:

  • AirNow.Gov: A government website that is generally ok, but they have fewer sensors and don’t necessarily cover your area well, though their sensors are strategically placed to represent the quality in that general area.
  • BAAQMD: Related to AirNow. It gives you an hourly forecast of particulates and further beyond.
  • PurpleAir Map: A map of sensors by PurpleAir. This site is more localized than AirNow, as they are crowd-sourced from more sensors, so you can get an idea of air quality closer to your location. The readings tend to be one color level higher than AirNow/BAAQMD sometimes. When I compare my Wynd Air Tracker reading with PurpleAir, it’s similar.
  • AirVisual: Another very good resource that sources their data from PurpleAir + extra features. This site not only shows you air quality more densely than AirNow, but it also shows you where the fires are and the direction of the wind, so you can kind of take a guesstimate where your bad air is coming from. AirVisual also has a very useful iphone app.
  • Wynd Air Tracker: This is what I carry around, move around in my house, to check the air quality. Used it for about 2 years now on a daily basis. Good quality and reliable. If readings get off-track, you can re-calibrate from the app. I also use it to test if my air purifiers are pumping out clean air, or not (time to change the filter).

Thought: When going from very clean air (indoor, blue/green range) to outdoor (red/purple range)… give your body a transition period. Let a bit of bad air in and let your body get used to that, before stepping out fully.

Building Your Own Air Purifier:

Once again California is engulfed with fires. This time, the air in my area has mostly stayed in the yellow range, teetering on orange at brief intervals. So I did further research on economic ways to keep the air clean because though we are all set at home, our kids classrooms don’t all have HEPA Purifiers and it would be nice if I could provide an economical solution.

From my research and with the assistance of my Wynd Air Tracker, I’ve successfully made a purifier with just a box fan, duct tape and a True HEPA filter refill.

How to build your own?

Materials Needed:

  1. A Fan with a flat face
    • The more powerful your fan, the speedier it will filter.
    • Try to match the filter/fan size. But if it doesn’t it will just take longer to clean all the air in the room, but it will still clean.
  2. A “True HEPA” is preferred (lower preferences are HEPA-type or at the very least a MERV12) Filter Refill. If you don’t know the difference, scroll lower.
  3. Optional: Carbon Filter
    • A carbon filter is nice to have to handle odors/VOCs
    • If you plan to use these year-round, only these two filters are ever really needed/useful… a TrueHEPA and a carbon one.
    • (All other filters are more gimmicks and not essential)
  4. Duct tape or some kind of fastener.
  5. Optional: a Sensor to test.
    • If you are using a TrueHEPA filter. You don’t need to test. It’s industry standardized and verified.
    • If you are using a HEPA-type filter or a MERV filter. You probably want to test.

What’s the quick/economical build I used above?

At these prices, you could afford to build several, one for each room in your home or even donate some to a school/community if desired.

How did I hear about this?

I’ve done some research online since the huge fires 2 years ago. I’ve found that other parts of the world constantly live with this problem, like China, while us Californians have only recently had to face this issue, so a lot of bloggers have posted their findings online. (Of course, I can’t do any testing until our own air turned bad, since it’s usually very good when not burning up.)

Here is the most comprehensive reference I found on DIY Air Purifiers (they even address the question of putting the filter in front/behind the fan):

Does the AC/Heating unit at home/work/school have its own filter?

It probably does. But those filters typically can’t be too dense otherwise it slows down the whole cooling/heating process of the building. Those filters are really meant to protect the system from clogs while letting enough air through.

A MERV12 and higher filter is the minimum at which it starts to filter some PM2.5 out of the air, and even that could slow down the air coming from the HVAC. The downside of slowing down the air flow is that it could result in mechanical problems to the HVAC system as the MERV12 or higher filter gets more and more clogged.

Someone wrote a good article to explain this issue here (The Unintended Consequences of High-MERV filters). So if air purification is your thing, it’s best to go for a standalone one.

What kind of pollution is in wildfire smoke?

According to the EPA (PDF), wildfire smoke predominantly consists of fine particles in the 0.4 to 0.7 micron range.

What is this PM2.5 I keep hearing about?

Particles in the PM2.5 size range are able to travel deeply into the respiratory tract, reaching the lungs. Long term exposure to fine particulate matter may be associated with increased rates of chronic bronchitis, reduced lung function and increased mortality from lung cancer and heart disease. People with breathing and heart problems, children and the elderly may be particularly sensitive to PM2.5. [Source]

What’s the difference between True-HEPA, HEPA-type and MERV filters?

  • MERV
    • Stands for Minimum Efficiency Reporting Value
    • Used for HVACS and furnaces
    • MERV ranges from 1-16 (17-20 would be in the HEPA range)
    • MERV12 is the minimum rating that starts to filter out PM2.5 particles. Iirc, it’s supposed to filter out ~50% of PM2.5.
    • MERV values are not standardized and varies from one brand to the other
  • HEPA
    • Stands for High Efficiency Particle Arrestance
    • For air purifiers (or HVACS with HEPA compatibility)
    • HEPA is equivalent to MERV17-20
    • HEPA-type filters are non-standardized. Imitations that were not tested by any authority.
    • TrueHEPA filters are standardized and rated to remove 99.97 percent of all airborne particles of exactly 0.3 micron diameter in a single pass.

Useful References:

Original Post from Nov 9, 2018

With the onset of climate change, California has been seeing spates of wildfires in recent years, causing unavoidable poor air quality sometimes for days.

Here are some tips for staying safe with the poor air quality lingering around:

  • INSIDE: Stay indoors and keep windows/doors closed. Use an Air Purifier
  • CAR: Turn ON Air Re-circulate in your car
  • MASKS: If you have to be outside wear N95 or higher rates masks. Don’t re-use masks, only new ones will work and must be tight to your face. These masks don’t work well on kids.
  • LAUNDRY: Wash all your clothes as often as you can, since particulates will linger in your clothing and get into the air as you take it off/put it on, etc.
  • MOP: Particles eventually land on the floor, so mopping or HEPA vacuuming is a good choice.
  • HUMIDITY: Keep you place at a decent level of humidity.

Finally… one way to keep the air clean at home is with an air purifier. 

I bought our air purifier in 2012 thinking I’d only use it on the rare occasion, who could’ve known that we now have to use it almost weekly. After some research, I settled on the BioGS1.0 from RabbitAir. It is many years old now and still running well.

  • Maintenance: My BIOGS1.0 is extremely easy to clean. I pull off the front panel, and remove 3 panels of filters. The pre-filter and charcoal can be vacuumed/washed. The HEPA filter, I just toss and replace.
  • Frequency: Maintenance every 3 months and replace the HEPA filter annually, if used 24hrs/daily.
  • Noisiness: It’s an extremely quiet machine, that I can leave running at night while sleeping.
  • Effectiveness: It cleans out a small bedroom in about 30 minutes and a large living room area in a couple of hours. (I used to leave it by the laundry room and would watch the little specks of lint/dust float into its grills.)
  • Automation: Option to self-adjust filtration level based on air quality using its two sensors (dust and odor).

This tides us over until the air outside recovers and we can open our windows again…

Update 11/13/2018:

I’ve also now begun researching portable purifiers for the car, since we commute so much and the re-circulate option is pointless when the air outside is filled with smoke and we are getting in/out multiple times a day. Basically, since our car doesn’t have a built-in HEPA filter, our bodies are the filters… breathing all that air that gets mixed in each time the door gets opened.

Update 11/13/2018 #2:

Every time I sit in my car, I start to feel a light headache. Even though we have the air on re-circulate in the car, due to the kids, the door stays wide open for long periods of time and bad air gets in and trapped inside. I searched for a car/portable air purifier and could only find cheap ones that break down in two months according to reviews. Finally, I found Wynd, a Kickstarter product that came out a couple years back. Sadly, Amazon, wouldn’t ship to my address but that led me to contact Wynd directly and I discovered that they were local in Redwood City.

Their customer service was very responsive and within an hour I was able to drive there and pickup two sets of Wynd Plus kits. Once I plugged it in and turned it on, I was shocked to see the air quality reading in my car.

Wynd Portable Air Purifer

(Amazon Link, sold-out, but you can still check the reviews. Update: Now sold in Apple Stores.)

Wynd ​​Tracker reading in my car

I kept it on and by the time I got home, it registered at:

After a 30-some minute drive with Wynd running in the car​​

I did notice slightly less smokiness in the car and my headache was getting lighter.

Once I reached home, I setup the Wynd Tracker around some spots in the home to see how my RabbitAir did. Surprisingly, my RabbitAir wasn’t doing so well. The air immediately around the RabbitAir was good, but everywhere else was also registering in the red.

The room adjacent to the one my RabbitAir registered very red, even though it’s connected by two hallways.

Air quality in the room connected to where my RabbitAir was running

And then the room where the RabbitAir was actually in:

On the far side of the room where RabbitAir was running on auto-mode

So even though we have the RabbitAir running on auto-mode, you can’t really quite tell if it’s doing enough (I should have probably set it to Turbo mode this whole time) without some kind of accurate sensor versus the little bars on the RabbitAir screen. The only thing we know is that in the car I had more acute headaches while at home I don’t, but clearly there’s a lot more purifying needed in the house.


1.) Portable air quality sensors are useful.

2. ) Car/Portable Air Purification is important (if you spend a lot of time in the car or at work with questionable filtration)

3.) Home Air Purification is important.

The little Wynd Air Purifier + Tracker covers 1 & 2. Now it looks like Wynd is planning on taking care of #3 as well. I stopped by their little startup office today and they revealed to me that they will be launching a new product tomorrow morning on Kickstarter that takes care of in-home air purifying with a more full-featured sensor.

Here are the links to the products mentioned above:

Update 11/16/2018:

Quote from Mercury News regarding prolonged air exposure:

“In Oroville and Chico, where unofficial air quality levels were around 500, breathing the air for 24 hours brought the equivalent health risk of smoking a pack of cigarettes a day, according to a calculation done several years ago by Richard Muller, a professor emeritus of physics at UC Berkeley. The “very unhealthy” levels in parts of the Bay Area would be like smoking half a pack, and the “unhealthy” levels reported elsewhere would be like five or six cigarettes.”

Author: nameless

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