Chemical Engineering in Daily Life – Question 27: Are those PM2.5 masks available on the market really effective? Standard answer already exists
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This post was last edited by yjqin1 on 2015-9-9 08:43. Everyone is terrified of PM2.5 – but what exactly is PM2.5? PM2.5 refers to particulate matter with an equivalent diameter of less than 2.5 micrometers. If a mask is capable of trapping PM2.5, its pore size must be ≤2.5 micrometers. I study microporous hydrophobic membranes; I have been doing this for 28 years. If a mask is to be effective, the pore size of its pores must be less than 2.5 micrometers. We assume that the average diameter of the pores in the membrane is 1.0 micrometer, the average thickness of the membrane is 50 micrometers, the average porosity is 50%, and the curvature factor is 1.5; the thickness and resistance of the support layer are ignored. The effective area of the mask is 60 x 60 = 3600 square centimeters, and the mask fits tightly against the skin with no gaps. What is the maximum pressure difference between the inside and outside of the mask when breathing normally? Do you feel short of breath? Can you tolerate it? What if there is a leak point on the mask with a diameter of 1 millimeter? For the specific calculations, please refer to my post – Interesting Chemical Engineering Questions - 2. I believe that the masks available on the market are designed to deceive people; they either allow air to leak through or the diameter of the pores in those masks isn’t as small as claimed, and it’s possible that it’s actually much larger than 2.5 microns. Then it won’t work either. That’s why I never carry any PM2.5 masks with me. If it really works, it would be better to cover your head with this kind of mask fabric (the effective mass transfer area increases by dozens of times). Of course, if it relies not on the filtration principle but rather on electrostatic adsorption, catalytic oxidation, etc., then it’s a different matter. The polytetrafluoroethylene hollow fiber microporous hydrophobic membranes produced by our company have been tested by Academician Zhong, and they are capable of reducing PM2.5 levels from 150 micrograms/m3 to 2 micrograms/m3. However, the gas flux is too low; even with the most hydrophobic, thinnest, and highest-porosity polytetrafluoroethylene microporous membranes available, they are not interested in polypropylene microporous membranes, considering them to have poor hydrophobicity and mechanical strength. My conclusion is that various PM2.5 removal technologies are suitable for air filtration in enclosed spaces. On cloudy days, it’s best to stay indoors (especially in places with air filtration), avoid going around, and certainly not exercise.
The original poster has analyzed this very thoroughly. It’s not a particularly complicated issue, so why are such masks still being sold openly? What on earth are the regulatory authorities doing?
Standard answer: If you buy a mask, you should choose one whose pore diameter is truly less than 1 micron, which is extremely thin, has an effective area large enough to cover your entire head, and whose gaps relative to your skin are also less than 1 micron. However, such masks are not available on the market. Everything else is just nonsense. It is estimated that various types of masks are quite effective at trapping PM2.5 ； In other words, it’s still effective to let businesses make $250.
It can’t stop haze, but it can block fog; just wear it as a makeshift solution: lol
It can’t stop haze, but it can block fog; just wear it as a makeshift solution: lol
It’s still better to buy qualified masks, as they are safer.
It’s just psychological comfort! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !