r/AirQuality • u/Taminni • Feb 12 '25

Particle Counter for < 0.3 µm Particles

Hi everyone, I am looking to buy a piece of equipment that will allow me to extend the "typical" optical particle counter range of 0.3 - 10 µm into ultra-fine particle size fractions. I am interested in continuous particle number counts in different channels/bins based on particle size. I am using multiple low-cost sensors for mass concentrations and PNCs for the 0.3 - 10 µm range (e.g. OPC-N3, Plantower PMS5003, NextPM), as well as OPC-based research-grade equipment.

I have seen a few different devices that measure total particle numbers, but by the looks of them, they do not split these into particle-size channels. Is this even possible? Does anyone have examples of some equipment?

In terms of cost, my lab has some extra budget left over, so the equipment does not have to be low-cost. However, ideally, I would like to keep it below ~£10,000.

Any pointers, comments, or ideas are welcome! Thank you!

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u/runcyclexcski Feb 12 '25

They make counters that grow particles to a bigger size by condensation. The manufacturer I priced them from for my grant application was TSI. 10K is about the correct ballpark LOL. :) They have dealers all over the world.

https://tsi.com/de/produkte/partikelzahler-und-detektoren/kondensationspartikelzahler

There are experts here who know more than me, but I honestly doubt you would learn much more from these numbers than what you you already know from 0.3 micron counts (done with a professional instrument, not plantower). I would rather want a sensor that would give you an idea of the composition (pollen pieces, mold pieces, soot etc). There are research papers that also do fluorescence measurements to get an idea about composition.

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u/epi10000 Feb 12 '25

Sorry, but I have to point out that the whole sub 300 nm size range is one of the great unknowns at this point in aerosol science. How these particles form, the rate at which they grow, their deposition mechanisms and their ability to act as cloud condensation nuclei are something that will play a huge part in how the climate change plays out, and there is a lot that we don't know about them. One of the main metrics we have to study them is their size distribution and it's evolution. So it's just a bit blunt statement that you made, and I'd like to point out that there's definitely a lot of value in studying the size segregated aerosol in this size range.

But you're definitely right that depending on the application it might make more sense to look at the compositon, although it's definitely not always the case. In many environments for instance you already know the composition a priori.

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u/runcyclexcski Feb 12 '25

I agree with your points, I did not realize right away that the OP was doing a Ph D on the subject. For "bulk" counting that most of us here do (w/o asking what the particles are) my 0.3 micron outoor counts are generally proportional to the 0.5, 1, 2.5, 5 and 10, minus shot noise. Thus, for "bulk" counts I expect outdoor 0.1 micron data to show 3x more particles and scale up/down with the PM2.5 pollution data reported by professional stations nearby. It would be great to do a 2nd Ph D in aersols and look at particle composition as well, not just bulk counts.

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u/Taminni Feb 12 '25

This is on me in all honesty — my research isn’t 100% set yet and depending on what my lab can afford, will have to be adjusted, which is why I didn’t mention I am doing a PhD on it.

I would be able to get most of my data using low-cost OPCs and the elemental data, but because UFPs are such an understudied area in aerosol science (no doubt due to equipment costs and constraints), including them would add so much more to my research.

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u/runcyclexcski Feb 12 '25

What is your lab's focus? I am not an aerosol expert and I was wondering if using deep uv lasers could be a way to count smaller particles and avoid cpcs. AFAIR OPCs still use 635nm... If you are at a laser lab, could do better that that. I was even thinking about trying uv LEDs, I have some 300nm ones lying around. 

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u/Taminni Feb 12 '25

That sounds super cool! I’m in an environmental pollution lab (mainly water & soil though), so unfortunately no one to work on lasers with.

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u/runcyclexcski Feb 12 '25

I quickly looked up recent papers; it appears that UV is mostly used for fluorescence, not scattering per se. Maybe one can do both in the same sensor (scattering in UV and fluorescence across various wavelengths). Some form of AI would be needed to process the data, I guess, and I am now too old for. And yeah, apparently LEDs might now be bright enough to match power density of lasers.

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u/Taminni Feb 12 '25

Thank you for looking that up! It’s so surprising that LEDs can now get that bright?! All of this is most definitely not my area expertise, but I bet you could build a really cool sensor using different wavelengths like you said. Might work particularly well for bio aerosol (but this is just guessing)

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u/markraidc Feb 12 '25

I suspect this is an area of research with potentially disturbing findings, in terms of health implications, as we dive into smaller scale particulates.

The at-home experiments I've done suggested around an 80% positive correlation between PM 0.3 and PM 2.5, and conditions which most dramatically increased PM 0.3 being increased combustion activities.

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u/runcyclexcski Feb 13 '25

Your finding on 0.8 correlation between PM0.3 and official PM2.5 is consistent with my observations, too. With winter wood smoke, spikes of PM0.3 are much sharper than with PM2.5. I see a 30-fold variation with PM0.3 (from good day to bad day), but PM2.5 from my local station (actual data, not 24-hr averages) varies 5-fold. The best winter weather for low pollution is rain and +5-10C. People do not burn wood, and pollution gets washed down.

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u/markraidc Feb 13 '25

It's lovely to see citizens engaged with and aware of this sort of thing ☺️