[Stoves] particulate size retention

[Xavier Brandao]

Dear Andrew,

 

« I'll take the liberty of reposting your question to Prof Lloyd about how come the smallest particles are more likely to be exhaled rather than absorbed through the lung membrane and his good explanation and response »

Sure! Thanks!

 

 

Dear Philip,

 

OK, thanks for the explanation.

Trying to learn a little more on that, but that’s not so clear.

 

This study here:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5735549/ 

says

« Matter with a diameter of 10 µm or less is considered suspended particulate matter, and matter with a diameter of 2.5 µm or less is considered fine particulate matter. Ultrafine particles refer to particles of 100 nm or less; by their nature, these particles do not readily sediment or flocculate, and thus have a longer retention time in the atmosphere than fine particles allowing them to be carried long distances by the wind [1 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5735549/#b1-eht-32-e2017021> ,2 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5735549/#b2-eht-32-e2017021> ]. In terms of health hazards, fine particles are only absorbed by alveolar macrophages when they enter the lungs, whereas ultrafine particles are also absorbed by airway epithelial cells, which can cause an inflammatory response in the airway. »

 

This one talks about really small ultrafine particles:

https://arstechnica.com/science/2010/11/why-do-some-nanoparticles-get-trapped-in-our-lungs/ 

 

« With particles smaller than 34nm, surface properties began to matter. Positively charged surfaces impeded the translocation of nanoparticles, while the negatively charged, polar, and zwitterionic surfaces allowed translocation from lungs to lymph nodes. The smallest zwitterionic particle (5nm) can be easily cleared from the body. They moved from lungs to lymph nodes within three minutes and into urine after just half an hour. 

The authors’ findings are helpful for drug design. For example, if you wanted to deliver drugs quickly to the blood stream and allow unused drugs to be cleared via urination, you would design nanoparticles to be around 5nm and avoid positively charged surfaces. On the other hand, if you wanted the drugs to accumulate in the lungs, you would design large or positively charged nanoparticles. 

The research results also provide insight into nanoparticle toxicity. Pollutants that are not positively charged and less than 34nm in diameter are fairly dangerous, as they can easily traverse through the body. Particle diameters between 6nm and 34nm are possibly the most toxic, as they won’t be easily cleared from the body; they could migrate around and accumulate in organs and tissues. 

The authors’ results agree with a lot of the existing data that relate nanoparticle properties with toxicity or therapeutic efficiency. »

 

Submicron particles indeed seem of the erratic kind.

 

Best,


Xavier

 

De : Stoves [mailto:stoves-bounces at lists.bioenergylists.org] De la part de Philip Lloyd
Envoyé : mardi 29 mai 2018 18:42
À : 'Discussion of biomass cooking stoves'
Objet : Re: [Stoves] ***SPAM*** Re: ***SPAM*** RE: Stoves Digest, Vol 93, Issue 5

 

It is difficult conceptually to even think about the mechanism whereby submicron particles interact with matter. I have suggested to you it is a question of momentum.  At the sub-micron scale “surfaces” are a moosh of electrons – that’s all you can see as you approach the surface.  You may be lucky, and be riding a particle which is looking for an electron, but even so with that excess of surface electrons you are likely to get repulsed. Alternatively you may be going fast enough (Boltzmann allows it) to dash through the Coulomb barrier. 

 

These probabilities are calculable and lead to low adsorption at less than 0.5 micron. I’ve given you a mechanistic, Newtonian interpretation, which is a good enough first approximation. Being more exact gets fun but some of the approximations you have to make are hairy.

 

Hope that gives some clarity

 

Philip

 

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