I think pore size is not much of an issue as filters collect almost all particles no matter pore size. You can read Hinds Aerosol Technoogy. Pore size is more related to pressure drop...

I think so too, but recently I met with some producer of PM samplers, that for the various factions recommended different pore diameter. So I started to doubt.

Actually, as you mention quartz filters, I guess is for ECOC or organic analysis. I usually just buy the pre-fired filters from the same lab that is going to analyze them (i.e., ChesterLab, DRI, Sunset). I think is better to work with the lab that is going to analyze your filters and use what they suggest.

Pablo

Anita,

I'm confused. Quartz fiber filters (QFF) do not have any pore because they are a mat and for this reason a pore size should not be a parameter. NIOSH uses QFF for collection of Diesel Particulate Matter in occupational environments - you should not have any problem in collecting particles less than 1 um and less than 2.5 um.

I have a question about your selection though. What tipe of analysis are you planning to conduct on the samples? If it is IMPROVE or NIOSH5040 the QFF are the best choice. If you are planning to conduct a gravimetric analysis, I suggest you to avoid QFF because the filter material is extremely fragile and you won't quantify any mass collected with accuracy. In this case PVC filters with 5 um pore size and the best pick for collection and modest pressure drop.

I hope it helps.

Emanuele

Hi Emanuele,

Thanks a lot for answers.

I am using Tissuquartz by Pall Corporation since 2010 and of course I know that my quarz fiber filters doesn't have pore size. I am analyzing samples for OC/EC, main ions, mercury, benzo(a)pirene but also mass. With that last one I know about problems...We weigh our filters after assuming the rings and then after sampling and conditioning also weigh them in rings. As a result, we do not have weight loss ...

My question was because I have met in one of the article Whatman filters QMA with 2.2 um pore size.

Anita,

I checked @colepalmer (http://www.coleparmer.com/buy/product/72088-whatman-quartz-filters-qm-a-4-7-cm-dia.html) and they report also 2.5 um pore size. I'm still convinced this does not make sense considering that quartz fiber or quartz tissue has a filtration approach completely indipendent from the concept of pores. It is possible that the pore size characteristic for a QFF was assessed by using the BET technique....the BET will give a theoretical number even if the material has no pores. But I would not consider this information important for my sampling when I use QFF.

Hi all,

I think pore size is kind of a construct. Teflon filters are also a mat and they report pore size. I think the pore size is an estimation not an actual measuremente (like in the nucleopore filters). It is important for filtration in liquids but not in air. I think pore size will be related with pressure drop.

Pablo

We routinely use Pallflex quartz filters (e.g. Mod. 2500 QAT ) for PM1 up to PM10 air quality sampling. In case of a fiber filter the "pore size" is sort of an effective parameter which can be used to describe the filter performance but it does not relate to the actual "opening" between fibers. Air filtration is not "sieving". Nanoparticles are removed mainly by the diffusion process. Super-micron particles are mainly removed by impaction of particles (collision with fibers). Check e.g. "Air Filtration" by R.C. Brown.

Yes it is like with deposition velosity of particles in air...

So we do use this same filters for our PM1 up to PM10 samples,

Also, if you have doubts you can put 2 filters in series and check if there is breakthrough...

Yes, that is good idea, especially that I have dual sampling system (FAI). I used to do such a check for teflon filters in the past

The second QFF in serie will always pick something but this does not mean breakthrough. QFF is particularly capable of absorbing organic material originally in gas phase or out-gassed material from the primary filter.If you run ECOC analysis on the secondary filter and you don't detect any EC, it is a good sign of absorbed gas OC.

Thank you all for very interesting and frytable discussion ;-)

Emanuele is right... good catch

I used PTFE filter of PALLFLEX that stay a pore size of 0,3 um, but with an efficiency of 99,9% for all particles. The only problema I had with pore size is the pressure drop of the sampler. You solved your problem? Is pore size a problem?