For the most part, these sensors have generated pretty similar results for the first few days of the inversion. PM2.5 at Hawthorne has risen fairly steadily during the period (with some ups and downs) with a range from midnight on the 9th to midnight on the 10th between about 38 and 54 ug/m3. PM2.5 at Neil Armstrong Academy (sorry for change of scale) was generally close to Hawthorne through midnight on the 10th, with the range from midnight on the 9th to midnight on the 10th of about 39 to 65 ug/m3.
It is above my pay grade to explain these differences. I know little about the measurement of PM2.5, other than it is very difficult, or the instruments used, other than the fact that the DAQ and University of Utah samplers are different. The discrepancy appears to have developed during a period when fog was in the area. I don't think this is a coincidence, but I lack knowledge of the sensor characteristics and atmospheric chemistry to provide a reasonable hypothesis why. I'd rather say I don't know than speculate.
As such, in future posts during this event, I will be referencing both samplers and mentioning the uncertainty at play.
Note, however, that the lower Hawthorne sampler was in the unhealthy category for several hours today and the 24-h average is now very close to the unhealthy threshold. Thus, even though there are uncertainty in the measurements, this remains a serious event.