Thursday, September 3, 2020

My Introduction to the Low Cost Sensor and DIY Box Fan Air Purifier

My Introduction to the Low Cost Sensor and DIY Box Fan Air Purifier

 A Storytelling by CARB Staff 

(This post is just my experience over the last week/nothing in the post should be considered an endorsement of any particular brand or guarantees of similar results)




Whenever I hear of low cost sensors for air monitoring, it is always in relation to their value, or lack of, as tool for promoting policy or regulatory changes.  


In addition to other recent events, the recent California wildfires highlighted other inequities that communities of color suffer. The maps of air monitoring sensors that I looked to for air quality information indicated that most are away from the communities that are the most impacted by cumulative burdens.  Lack of awareness on the part of government, or EJ advocates, did not lead to this; it was a lack of awareness on the part of residents. These low cost air sensor monitors exist in other communities, without their use having any intent to address environmental justice, change policy, or effect regulatory changes. They exist there for people with knowledge about air quality, to make informed decisions regarding their outdoor activities, and indoor ones as well. 

I vented to my CARB colleagues about this inequity around the availability of information, and some responded by pushing this frustration forward.  We found an understanding ear, which was critical given the recent wildfires, which created some of the worst air quality in the world. 

This raising of concerns led to me receiving several air monitors that were part of a study. I deployed three of them to an area without existing air sensors within hours, and to a community that is also in the 95% percentile for drinking water per CalEnviroScreen. I spoke with the monitor hosts, in general, about Environmental Justice, air quality and its health effects, as well as CalEnviroScreen, while trying to install them. 


At one home, they had the router replaced last year by their service provider; who transferred the previous router’s network name and password to the current router.  Thus, it did not match the sticker on the router I was working with.  This was done as a courtesy to the primarily Spanish-speaking resident, so she would not have to trouble herself with knowing all that information.  She never had a need to know it; her devices just connected to her Wi-Fi automatically. I spent three days trying to figure out the password.  Finally, we called the service provider and they explained what they did, and fixed the problem over the phone. Setting up a monitor is supposed to be a five-minute process, and I got frustrated; but I ate really well there one day: a Purepecha soup, Uruapan Style.  


At another residence, I also struggled with setting up the monitor.  I asked Brian from the Office of Community Air Protection for help.  He is very gracious and agreed to help whenever it was convenient for the resident, Eddie.  Both indoor and outdoor air monitors went up at Eddie’s house. (Thank you Bro). Later that evening I received a text from Brian, “Is Eddie’s door open?”  I instinctively reacted as I expect many community folks would, “are you watching us?”  But, I realized, almost as quickly that it was just CARB staff being CARB staff; they love data. Brian was curious about Eddie’s indoor readings because they were close to 200 on the Air Quality Index (AQI).  I was glad Brian checked; Eddie is my friend, and I grew worried. I started following his indoor AQI readings too.  

Separately, I had purchased a monitor with plans to deploy it to a monitoring void, as well.  However, since I now had several air sensors, I decided to activate the one I bought, at my home and indoors.  The air sensor company allows for moving a monitor to other sites, which I still plan to do; but this will allow me to learn more about air sensors.  I had the same indoor readings as Eddie: close to 200.  If you are a parent, you know your children are the first thing that comes to mind when something dangerous is near.  Those readings made me believe that I had failed in protecting my children. I felt bad.

Dave, from CARB’s Monitoring and Laboratory Division is a good guy too! He sent me a picture, and suggestion that might help address the indoor air quality in my home.  I had nothing to lose, and everything to gain, so I tried it.  As you can see from his picture, he suggested putting a low cost filter in front of a fan.  By this point, I am in constant communication with Eddie, Brian, and Dave.  Eddie and I are learning as we go, and Brian and Dave are helping to answer questions.

So, I get home from the hardware store and unbox the fan and air filter with as much excitement as I would any plant or coral (my hobbies).  I tape the filter to the front of the fan in the direction the flow should go. I then get some paper and a pencil to log the time, readings, and gap between outdoor/indoor air readings, as I fire up the filter fan.  I am sharing all this with the three monitor hosts and CARB staff in real time: they were curious.   

When I started the fan, my indoor air was reading around 170, and the nearby, outside air sensors were reading in the high 180’s.  By 5 pm, my indoor air was around 80, and the outside air was in high 150’s.  I bought a second fan and filter to see what that will do; and it brought the numbers down to the mid 60’s, surprisingly fast.  

I posted about this on Facebook, and folks responded by offering me brand new filters they had lying around.  Trish, my EJ Unit colleague, and friend, shared a tweet from someone at the AG's EJ Bureau that built a box fan filter for an elderly neighbor, with the hashtag #cleanair. I also heard more from Dave.  He told me that he put an air filter in his baby’s room; after he was shocked to see readings near 200 there. His colleague in the research division suggested the box filter fan. 

There are many things about this story you should know:  The air sensors only measure particulate matter; and will not show you the levels of gases or other pollution that could harm you; this is not a scientific study, but rather a story of citizen science; and not and endorsement of any brands displayed in the pictures. Box fans are NOT intended to run 24 hours a day.  They should NOT be run if you cant attend to them due to risk of overheating. There is also a box method to building a box fan (see link below) which reduces the risk of overheating the fan motor. Please read the air district guidance document in the links below.

Thus, the low cost air sensor can been seen through a greater lens than regulatory processes or AB 617.  It can serve as an educational tool for the community.  It can create an interest in understanding air quality and protecting loved ones using air quality information. That can lead residents towards pursuing actions to improve their indoor air pollution, with low cost options. 


CARB folks, like MLD where Dave works, are hoping to create a curriculum for youth to build their own air sensors, at ¼ the cost of purchasing air monitors. That could be followed up with a curriculum for youth to conduct experiments with box filter air purifiers, using the air sensors they built themselves. These could be projects for the youth science fairs, that have potential to provide benefits as they are conducted.

I can personally say that I felt very empowered after seeing the indoor air quality readings improve in my home. I was able to immediately effect a change for us. I also felt empowered by being able to stay abreast of the air my family & friends breathe; I can let them know if I see unusually high readings.  

Its not just me that's enthused, Eddie has been sharing what he has learned with his family & friends through social media. He's been happy to learn about this. And that has led to requests from his contacts, to connect with CARB grantees or government in an effort to learn more.  

I'll add, both Eddie and I own lowriders, as do/have the other two monitoring site hosts.  None of the monitor site hosts are the typical folks that many people, or agencies, working in the EJ field, reach out to on environmental issues.  And yet, we've all embraced air quality information to help inform decisions that may protect our families health, based on being empowered with the same information others have access to.   

That is my experience with a low cost sensor, after one week.

Now, lets see about starting the first EV lowriders car club. ha! 

Jose Saldana

CARB Environmental Justice Unit



For SAFETY, please follow these precautions:

  • Don’t leave the box fan air purifier unattended.
  • Turn off the box fan air purifier while sleeping.
  • When the fan is modified in this way, use the device as an air cleaner, not as fan to cool your home




Here are some useful links:

(Safety Guidance from Air District)

(Variation on the box fan)

(Box Fan Filter vs HEPA)

(Usefulness of low cost sensors during wildfires)

(YouTube DIY Tutorial)  



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