Our lab build and characterized one of the first low cost mobile PM sensing devices and worked with a major manufacturer of reference devices. I think the artic

Our lab build and characterized one of the first low cost mobile PM sensing devices and worked with a major manufacturer of reference devices. I think the article is partially over simplifying. This is because also the reference devices do some tricks to derive mass concentration. Real mass concentration can only be measured at a low frequency by using actual filters that absorb the PM in the correct size category. Optical and beta attenuation devices are actually calibrated. The question is if the translation of absorption and count is actually so stable against mass. If you use other types of sensors like nephelometers you can for sure get different readings, however: are they really more wrong? Particularly if due to the measurement pricinciple a higher resolution is in the data. If you would want to measure mass concentration you would need to compare against real mass concentration and aggregate values. I am not sure if high resolution RSME is really helpful as a metric here. Constantly in place calibrated low cost sensors are often quite good. But this does not tell so much about their quality. In the end it is what you want to do with the sensor. For regulatorybpurposes (measuring e.g urban background) the placement of the sensor is often more important than the accuracy. If you want to discover relative and transient effects a well calibrated network of dense low-cost sensors might be a fit. In the end you cannot even easily translate exposure to harm, because it the material of your PM very likely will also matter (we are just assuming the typical mix in most cities when deriving limits)