[schiffern]

>Unfortunately I can't create this kind of machine (software eng, no hardware skills), but I think there is a very big market for portable masks with safe air

You may not need to DIY (much).

I recently posted my experiences and tips with the AirPro mask,[0] and the response was at least entertaining! Tl;dr it's a wearable HEPA device that pipes 99.97% filtered air into any N95 mask. Besides improved filtration, this also prevents the hot humid mask feeling that some people dislike.

You might consider adding a carbon prefilter (look for sheet filter medium and cut to size) for the HEPA unit, and pairing that with a carbon N95 mask (eg 3M 8247). This should filter several pollutants of concern you mentioned, including nitrogen oxides, sulfur oxides, and ammonia. Sadly CO is nearly impossible to filter.

For indoor filtration, you might find some MERV-13 filters[1] and make a Corsi Box[2]. No engineering skill required, just a bit of duct tape.

Maybe something here will help! Cheers and good health

[0] https://news.ycombinator.com/item?id=34378478

[1] https://news.ycombinator.com/item?id=34797981

[2] https://cleanaircrew.org/box-fan-filters/

[cmews]

This comment made my day! I'm going to give it a try and will convince my wife to test it to see if it helps :)

[schiffern]

Glad to hear it. :)

A couple tips I forgot, some of which may increase the all-important "wife acceptability coefficient":

- carbon tends to get saturated pretty quick, so in regular use I would replace the (cheaper) prefilter at least weekly, mask every 2-3 weeks

- testing may show you can get away with a non-carbon N95 and just the carbon prefilter; cheaper and the look may be found more acceptable

- carbon will immediately start adsorbing pollutants from ambient air, so keep all unused carbon in a sealed jar or sealed original packaging

- have fun with it! At Starbucks and pizza places I'm either Mr Snuffleupagus or Discount Darth Vader :D

- Corsi Boxes can be loud, so I use Low if people are around (High only for unoccupied space); shrouding or draping with fluffy towels can help too (hint: not the good towels)

- if you have forced air HVAC you might start out just using a MERV-13 filter in there; I prefer Filtrete 1900, but in general anything with many pleats = low pressure drop is better; most HVAC is not rated for large pressure drops across the filter

- I've had good success making an experimental "Carbon Corsi", taping two cheap 20x20 filters together with ~2 lb of replaceable aquarium carbon in the middle (change every ~two months) and taping that on top; this filters gaseous pollutants in the home, and can further muffle the box fan

(sorry, I swear this list was two items long when I started...)

Hope she can find some relief via your mutual efforts! Severe asthma can feel almost like a prison, so it's important to be extra kind and patient. Best of luck you guys