I performed several ICP-MS analysis of PM on quartz filters. I found that for some samples the concentration of some target metals in ng/m3 was higher in PM2.5 than in PM10. How could it be explained? The two lines sampled the same m3 of air and the sampler (Tecora Echo) were set close to each other. The mass of PM10 was higher than PM2.5 but the concentration in ng/m3 of only some elements was higher in PM2.5 than in PM10.
Thank you in advance.
Hi there
What method did you use to extract the metals from the filters?
When in suspension, for many adsorbents, the smaller the particle size, the more adsorption capacity for metals.
Not always as this also depends on the surface area of the porous material, but in general that is the case and I will not be surprised to find more metals in the PM2.5
Element composition and their concentrations might differ for fine and coarse particles depending on their sources and formation mechanisms. Even if you collect them from the same location, their sources might be different. For example, in urban environments most of fine particles will originate from automobile exhaust emissions, industrial emissions, heating and cooking activities etc. while coarse particles will originate from soil dust, road dust, pollens etc. In addition, for particles originating from the same source, adsorption efficiency of fine particles for some elements (depends on surface area to volume ratio) will be greater and this will increase their concentrations.
Thank you guys for your answers.
I have this question because I thought that sampling PM10 always provide for the sampling of PM2.5 (fine fraction) + the coarse fraction of PM. Based on your answer I understand that sampling with a PM2.5 cut head I do not get the same PM2.5 fraction that I would sampling by using a PM10 cut head.
Using the PM2.5 head, is the PM2.5 more "enriched" by the finer fraction of particulate matter compared to the sampling with the PM10 head?
Thank you in advance.
Sacha, Sinan is right. It depends on the source of the elements. Check for instance these two studies, where a dichotomous sampler for PM10 and PM2.5 was used. The auhors found - depending too on local sources - higher levels of some trace metals in the PM2.5 fraction compared to the PM10 fraction.
Trace Elemental Composition in PM10 and PM2.5 Collected in Cardiff, Wales, Mohammed, G, *, Karani, G, , Mitchell, D, http://bit.ly/2ynw8a5
Chemical Characterization and Source Determination of Trace Elements in PM2.5 and PM10 from an Urban Area,
Northern Jordan, Idrees F. Al-Momani, Wisam M. Shatnawi, http://bit.ly/2ymX8qc
Hello Sacha,
Theoretically you should be correct, concentrations in PM10 should not be larger than in PM2.5 because PM10 should include PM2.5. Still, cases happen where the concentration of some elements in PM2.5 is much larger than in PM10 subtracted PM2.5, and in these cases, a fraction of the material going into the PM2.5 sampler, might be lost in the PM10 sampler. Have a look at my paper from 2009 on Cl in PM2.5 (Science of the Total Environment 407 (2009) 5726–5734, https://www.sciencedirect.com/science/article/pii/S0048969709006731), it may look interesting and give you some hints to the solution of your problem.
Hi Sacha,
are the differences very big? Are they statistically significant? If the differences are small, it might be due to the errors associated with the measures.
I agree with you that PM10 includes PM2.5 and therefore the concentrations in PM2.5 should not be larger than PM10. Of course the PM2.5 and the coarse (PM2.5-10) fraction are affected by different sources, but since your 2 samplers were close to each other they should be affected by the same sources.
Then, I agree with Leonardo Pantoja that it might be due to some methodological issues (either in the chemical analysis or in the sampling intself).
Regarding your question about if the PM2.5 might be "enriched" by the finer fraction of particulate matter compared to the sampling with the PM10 head, I don't think this should be the case if the samplers are used in the conditions specified (specially air flow) by the manufacturer to sample each of the fractions.
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