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Comment by mikeyouse | Hacker News Reader

Does anyone have a sense of where the damage is done regarding PM? I live in SF and our apartment is a block away from a busy road and a gas station, both of which concern me. Not to mention the wild fires of late depositing ash all over our yard.. Also, being a SF apartment, there isn't A/C so we leave the windows open on hot days.

Is there data around whether an active air filter running in a closed room before we go to sleep will help? Should it just run constantly? Is there any good method to actually lower the amount of PM I'm inhaling?

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PM2.5 are mostly secondary organic aerosols, meaning particles that form after the reaction of other emissions. Unfortunately these can occur even with chemicals that have traveled for days and then they react with local emissions. So if you live in a forest which emitts a load of pinene and other organics and due to microclimate you receive NOX etc from a city not that nearby, boom you get very high PM2.5.

Purpleair.com has a map of of sensors that update in near real time you can look at.

That is a cool site. I had not known there was such an extensive sensor network out there.

One thing to remember about the kind of location the parent comment wrote about: particulates are very local. Trace gases like O3 or CH4 can have very sharp spatial gradients - e.g., near highways, major streets, or dairy farms. You can observe sharp decreases from emission levels to background levels within 10s of meters. And PM2.5 mixes even more poorly than these trace gases, meaning PM2.5 shows sharper gradients.

So, if you live in a built-up area and you really want to find out about PM2.5 due to your open window, or on your patio or backyard, you may need a very close-by measurement.

You will still observe correlations between health outcomes and mean PM2.5 within, say, one 1km^2 monitoring footprint versus an adjacent footprint. So the background level is definitely telling you something.

I bought a AirMega last year. It always runs on "quiet mode" and the PM2.5 is below 5 all the time in my 900sqf apartment. http://airmega.com

Does it work well for a multiroom apartment?

You can use www.breezometer.com to check real time PM2.5 readings in your location. Based on that you can figure out whether you need an air filter or not.

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