Originally Posted by
genejockey
Remember, AQI is a unitless number, and the point of the conversion is that PurpleAir's inexpensive sensors apparently tend to give a higher reading on wildfire smoke than more expensive ones used by the EPA, and LRAPA just brings them more into alignment. It doesn't change the air.
I've found PurpleAir to be fantastically useful this month! The large sensor network lets you see developing trends, like seeing the numbers rising in the San Mateo Highlands while it was still nice and clear in the flats. I knew what was coming. Same thing happens when it clears - I can see it coming. "AirNow" is just too slow to see the short term trends, and if you plan based on it, you'll either find yourself riding in smoke, or huddled inside when it's nice and clear outside.
Totally agree - AirNow is useless because of the one- to two-hour lag time, and Purple Air is infinitely more useful to us cyclists because it gives you localized and regularly updated readings for whatever area you plan to ride in (except for super remote areas). I'm just skeptical of the LRAPA conversion because I've had too many instances where the LRAPA numbers look pretty good, but then I step outside and I smell and see smoke.