Particle size versus Particle mass. (by Diego Fdez-Sevilla)
“Hollow particles are common in the atmosphere, then instruments that measure particle size cannot be used to obtain particle mass (TSP)” was the comment by
I have worked with airborne particle sampling methods and what I can share about it is that in Germany they used Glass fibre filters for two different analyses. One to measure Total Suspended Matter based on the weight of the filter, and the other one to measure Black Carbon concentrations based on measuring the optical absorption and scattering of light by the particles collected on the filter tape. Also, I worked for a while at the DWD in Freiburg looking for the best filter material suitable to perform these two methods plus, to use fluorescence and white light in order to identify pollen grains due to their synergistic effects on allergenic reactions when combined with pollutants (SO2, NO2, NH3 and VOCs). When using filters for particle sampling there is always a factor affecting the original state of the particles from when they were airborne which is the effect of having a constant current of air passing through the sample throughout the whole sampling period (which might be 24 hours). A combination of measuring particle size and particle weight might be closer to identify the role of each particle type in the total weight of the sample. When talking about reactivity, I believe that the method applied has to be defined based on the technique selected to analyze the sample. The process of particle sampling has to keep unaffected the properties in the particle that you want to measure, and I believe that is the challenge.
Just to add a little bit more, the challenges that I identified in my research about particle sampling started not only with the fact that the process of particle sampling has to keep unaffected the properties in the particle that you want to measure, but also, in order to have an accurate sample of particle concentration from your atmosphere it is very common to have a deviation from the real concentration due to sampling efficiency inaccuracies. The devices applied to capture by suction at the same time airborne particles of different sizes and shapes tend to overestimate or underestimate concentrations due to the different aerodynamic behaviour of the particles under the lack of isokinetic conditions (meaning that the air carrying particles into the sampling inlet has a different velocity of that the air carrying the particles in your environment). In my case, I studied those effects in sampling pollen grains. Pollen grains can take or release water when they are airborne (harmomegathy) so their aerodynamic behaviour changes with the environmental conditions which, altogether with the outdoors changing wind speed, affect the sampling efficiency of the instruments (also wind direction might become an issue if the device is not facing into the wind during sampling). With pollutants which might become part of crystals I suppose that parameters like humidity could also affect the measurements by the size of the crystal. Same with those particles which might react with others creating bigger or smaller structures. But that is just a guess.
Matters of discussion on LinkedIn are limited of participation to LinkedIn members or even just members of groups so, in order to reach as much contributors as I possible can I will share my take on those discussions I join in LinkedIn also in this blog to enhance participation aiming to “fill in” or to “find out” relevant gaps.