From: Web Link

Empirical studies have found that PurpleAir monitors tend to yield larger AQI values than regulatory agency quality monitors like those used by AirNow (see end of this article for more on why) when measuring wood smoke. To correct for this, the Lane Regional Air Protection Agency has developed a conversion formula that is built into Purple Air.

To apply the LRAPA formula, click the word “None” and change it to “LRAPA”. When you do this, you’ll see numbers that are on the same scale as AirNow. Without this conversion factor, you are comparing apples to orange.

Can you imagine this combination.

First COVID forces us to Shelter In Place closing all the local businesses. Then they get an idea and create open air dining on Castro Street.

Then what happened, the firestorms that are hitting us, in effect making it dangerous to try to breath outdoors. Which in effect closes all outdoor dining as well.

And what do I hear, the GOP backers say it is fine for people to die. They say it is acceptable for people to die of COVID, and now you can get seriously ill from smoke too.

I am now feeling like there is no light at the end of the tunnel, or the light we were told was their was the headlight of an oncoming train.

I live with Major Depression, and this situation is making me feel so much worse.

Hang in there, @Steven Goldstein. You're right; this is awful. But the fires will go out and things will get a little better eventually.

Ditto, BDBD comments to Steven Goldstein. Hang in there...it is really hard right now, but things will get better (unless there is an alien invasion, in which case all bets are off!). Seriously, many of us read and follow your posts here and want you to hang in, help us all work our way through this. Be as kind as possible to others...everyone is feeling it in different ways.

PurpleAir measurement system. @ Cat: Independent of the "P2.5" absolute calibration, I find this systematic "citizen science" air particle measurement infrastructure extremely impressive and useful. I have been 'checking the graphs,' 'under the dots' near my house this last week more than I did 2-3 years ago.

The LA area South Coast Air Quality Management District did a detailed study (linked elsewhere/ like Purpleair.com) of 'consumer grade' sensors and found theirs very good / as referenced to 'professional-scientific grade' measurement instruments. As a professional 'scientific instrumentation' person (though not in air environmental quality field) I'm 'totally fine' with using their "MAP" AS IS. I don't need a 10% 'absolute reference' when the measurements are varying by 200%!

Here is how I 'look at the data" from MAP. The SPOTs show the P2.5 # (which is the particles 2.5 micron and smaller = smoke). Clicking on them shows the graph (10 minute 'average from the machine'). I SEE HIGH SIMILARITY /correlations/ between the ups-and-downs and numbers in all nearby independent sensor stations. GREAT.

This system seems to be good! Good Gage R&R we would say (engineering wise). There is good resolution in both # and time, and good repeatability in the system. The 'calibration' reports/studies show that there is good 'linearity' which allows the Cat and others, more "wonk" room.

Thanks @Cat, read your link to UC Berkeley data science Prof Hug's posted article. In summary - at the end - he highly recommends Purpleair / their data is displayed 'almost real-time' with a 10 minute cadence. And he confirms - it has MUCH MORE on-the-ground (spacial) resolution than the 'official' EPA network.

As another UC (trained & staff) person, with FDA medical-industry experience, I'm a little unhappy with "EPA PM2.5" labels. THESE ARE NOT ABSOLUTELY CALIBRATED sensors / with any EPA, NBST or ISO 'traceability' once they are in-the-field. The basic technology of Purpleair measurements, seem to be a Nephelometer*, using visible (solid state) small lasers, in a "dual" system. Pretty darn robust - and the dual sensor system seems to be excellent for automatically detecting sensor problems - and perhaps automatically removing problem sensors (and readings) from the MAP. * wiki link Web Link

In astronomy, we have lots of "EPA PM2.5" calibration standard type problems. How bright a star? B (blue) magnitude of a 1st magnitude star is not the same as it's "b" (blue) magnitude. Astronomy's advantage (if you control for sky transparency) is that the "Standards" (stars) are usually available night-after-night / for free / to almost every astronomy observer in the world (and the several satellite observers 'out of this world').

check Purpleair.com MAP before you run, or air-out your house. IMO