What does "No" mean?

On the PurpleAir map page, after clicking on a site, the upper left of the map opens up to show the graph of that site over the past few days. Clicking on the top of the graph gets you to a drop-down menu. The second line of the drop-down menu is Apply conversion: with a box providing several different “conversion factors” the first one called “No”, the next “ALT CF3”, then “EPA”, etc. Clicking on the “i” icon next to “No” we find that “No” is defined as “No conversion applied to the data”.

However, there are TWO data files provided, called CF_1 and CF_ATM. Which of the two are we looking at? The Plantower manual defines CF_1 as for use in a “laboratory” while CF_ATM is “atmospheric” and recommended for use in environmental conditions. I downloaded an outdoor and indoor dataset, and by matching the downloaded concentrations to a concentration that I took from the map, I found that the outdoor data set is using the CF_ATM algorithm while the indoor dataset uses the CF_1 algorithm.

So the answer to the question above is: "It depends: if the site is indoors, “No” means “Use the CF_1 data” and if outdoors, “No” means “Use the CF_ATM data.”

On the other hand, using any of the other conversion factors, all of which depend on peer-reviewed published studies, will get better (always lower) more dependable PM2.5 values than either of the Plantower proprietary algorithms.

So maybe the answer to the question should be “I don’t care what “No” means; I’m not going there”!