[dognotdog]

While I admire the efforts of the SC-AQMD, and generally agree with the article, using R2 from a higher-end, but not quite perfect instrument, can be quite misleading, and is not a great indicator of actual sensor performance. Also, there are a lot of potential improvements in sensor tech, but instead almost everyone is relying on the same cheap sensor modules instead of innovating, which have have pretty bad deficiencies, especially in detecting particulates in the ultra-fine range, and don’t age very well. But, they are the cheapest.

[ahaucnx]

The R2 is between the tested monitor and the AQMD reference instruments (BAMs and Grimms). They also test if the two reference instruments agree with each other before calculating the correlation to the tested monitor.

So I believe their testing method is quite accurate.

[dognotdog]

This is probably a longer discussion, but PM0.3 (anything less than 0.3 microns) is quite difficult to measure, especially optically, as light scattering drops off very steeply once your particle sizes are around the wavelength of the light being used. Anything short of an SMPS class instrument that “grows” small particles through condensation so that they appear large enough to be counted, will not see much below 0.3 microns. Also, the total MASS of small particles might be low, but if you look at count, or lung-deposited surface area, we get a different picture. Especially around 0.3um, particulate matter is prone to get deep into the lungs, instead of being caught in the upper airways, and the small size means larger relative surface area, and thus higher reactivity. Even smaller nano particles might not go as deep, but are more likely to enter cells or the bloodstream due to their minuscule size.