air pollution particulate sensor package

Cars aren't bad. Diesels, in busses, trucks, and construction/farm machinery, are.

I'm a bit skeptical about the evils of CO2, but particulates are nasty for people and the planet.

Particulates melt snow, which is especially evil.

Cars aren't bad. What about thousands of brake linings turning to powedery dust at a Stop sign ??

Epithets deleted! that dropbox keeps squirreling around inside my system and trying to do something, searching for things?

Twice that URL crashed my system [now THAT's malware control!, simply crash if someone tries to muck about]

(I think dropbox got upset when I wouldn't sign up)

Anybody have a 'clean' URL for this?

Depends on whether the dust falls to the ground or is fine enough to become airborne. ...Jim Thompson

Probably bigger particles. It's the really tiny stuff, like 100 nm, that makes it deep into your lungs.

The dust is pretty large compared with diesel smoke particles, so it doesn't penetrate very far into your lungs. They got rid of the asbestos awhile back, which was a pity. Chrysotile asbestos is nasty, serpentine basically isn't.

Cheers

Phil Hobbs

Unless you use reflection, like in an optical smoke detector. Then 0% is the baseline. He could probably count individual particles.

From the way that stuff migrates all over the wheels on my car, I'd say it's pretty 'airborne'

Remember when the linings were made of asbestos? Which subsequently have been removed from the market. Coincidentally? after reports finding high levels in lungs of people who live near stop signs vs middle of the blocks, more open areas.

Den tirsdag den 1. juli 2014 00.27.52 UTC+2 skrev Robert Macy:

it the particle size that's important, if they are big enough it is is just dirt it is when they are small enough to get deep into the lungs and stay there is gets dangerous, like asbestos and according to some exhaust from modern high pressure diesels and gasoline direct injection

-Lasse

Yup. Dark field light scattering is the easy way to do it, if you don't need to go much below 0.5 microns. That's really simple--two air tubes, a simple vacuum pump, a laser diode, a lens, a collecting mirror, and a photodiode/TIA.

If the OP doesn't need size information, a condensation nucleus counter is the way to go. Those draw the air sample into a supersaturated butyl alcohol vapour, so any particles nucleate droplets.

Interestingly, the droplet radius grows linearly with time, so even a really really small particle (10 nm or so) produces just about the same size droplet as a 1-um particle.

Cheers

Phil "former crud guy" Hobbs

It's called a nephelmometer and uses light scattering. I have a Nikken #1394 Air Quality Monitor: I don't think this model is sold any more. The photo is me using it to find the source of the burning smell in the office. It turned out to be an overheated resistor inside the UPS in the photo. The unit is quite sensitive. I can stamp my feet on the rug and cause the graph to almost go full scale from the dust. Same with a couch or chair. You could probably clone the function quite easily.

More: Overkill:

Yes, particle size is key. Over 10um, the danger isn't so high. The respiratory system tends to clean this stuff out before it gets the lungs. At 2.5um the particles are a perfect size to get into the lungs and stay there. At some point, though, particulates will pass through the alveoli walls, into the blood stream (where they may be toxic or simply cleared from the system).

When I look for dust management for woodworking, I make sure the filters will filter 1um particles (about the best that can be found). Wood isn't generally toxic (though some species certainly are), though, so 1um is likely good enough.

I could not find a user manual for your Nikken. If you have a pdf and can spare the time, could you upload it to your web site?

This is a very interesting way to use a particle counter. I have some questions:

How does the Nikken operate?

Is there a table showing the particle concentration vs size?

What type of resistor was it?

Why did the resistor give off particles?

Was it hot enough to give off smoke?

Could you detect the source by smell?

I use the Dylos DC1100 PRO, which is a laser particle counter. It shows the particle count for two size ranges of particles: 0.5 micron to 2.5 microns, and greater than 2.5 microns. I believe it discriminates between particle sizes by measuring the width of the pulse as a particle passes through the light gap.

I have two units and I am always amazed at how well the readings agree between them.

I wonder how the Dylos and Nikken would compare in ability to discriminate between different size particles. Does the Nikken have more size ranges?

AFAIK size measurement is always done by thresholding the pulse heights. The scattered light power goes as the sixth power of the particle radius. (I've recently reverse-engineered several such units for two court cases, and they all worked that way.)

Cheers

Phil Hobbs

Thanks. I was working from some description I found online, but that makes a lot more sense. It is far easier to discriminate pulse amplitudes than pulse widths.

I wonder if the scattered light power flattens out above some radius? For example, if the particle size is above 2.5 microns, does the scattering change? For example, Raleigh scattering is effective for particles much smaller than the wavelength of the light. I believe it goes as the fourth power of wavelength:

Other approximations are used for larger particles:

It's hard to tell which approach would be best suited for typical air quality measurements, such as mold spores and dust particles.

Yes. When the particles are big enough to be really opaque, they start looking like geometric obstacles, so that the scattered light goes like the intercepted area.

A fine point is that as the particles get larger, the light scatters into a smaller and smaller range of angles around the incident k vector.

Dark field light scatter, where the laser beam, air flow, and receive path are mutually perpendicular is good medicine. Being 90 degrees off axis reduces the dynamic range, because larger particles, which scatter a great deal more light, scatter most of it in the forward direction.

Interferometric systems, which are sensitive to amplitude rather than intensity, don't suffer as badly from this. (Power goes as amplitude squared.)

Cheers

Phil Hobbs

vector.

Boy, this sure got complicated very quick! So many issues on scattering angles, changes with particle size, orientation, intercepted area, etc.

It's difficult to figure out what the system is actually measuring. Of course, I understand this is one of your specialties, and you really did some marvellous work at IBM on measuring particles in the presence of huge interference.

And thanks for the note on interferometric measurements. That's another area I need to look at.

Very interesting thread. Thanks. I will now be a lot more sceptical when I see some marketing hype on a new particle instrument.

Sure. I'll scan it later tonite.

My guess(tm) is by optical scattering. The light show is inside the black box with the air hose intake. See photos below. I didn't take apart the box, but with 4 wires going into the box, it's a likely guess.

No. The manual has a table by concentration: Level Color Particles/Liter 1 blue 500 2 yellow 1000 3 yellow 2000 4 yellow 3000 5 red 4000 6 red >5000 I presume that it's measuring dust particles, not aerosols.

It had a ceramic case, so it could have been either metal film, wire wound, some kind of bulk resistivity component. Most of the smoke seemed to be coming from the scorched PCB.

It didn't. The PCB is what was producing the smoke.

It was hot enough to scorch the PCB, so I didn't think it would be useful to also burn my fingers. Also, it's not very safe to shove my fingers into a live AC powered device. I had an IR thermometer handy, but neglected to use it.

No. The entire office was full of burning resistor stench. There was no visible smoke. I've had some experience chasing down overheating computers and power supplies inside server farms. The concentration of potential smoke sources and the high volume dispersible nature of the air flow in an ISP's server farm makes this a difficult problem. Lacking an IR imager, I just shoved a rubber hose into my nose, and sniffed for maximum smoke stench among the multitude of exhaust ports. About ever 15 minutes, I had to go outside to clear my nose. The olfactory sensitivity comes as a side effect from being a werewolf:

Sniffing for smoke in my small office created a different problem. The flow of HVAC air would disperse smoke over the entire office making it seem like everything was belching smoke. I immediately turned off the ceiling fans. That helped but required that I purge the air about every 10 minutes to prevent a build up of too much smoke.

I also made the mistake of thrashing around the office, disturbing books and boxes laden with dust. Just touching a computah would cause it to unload an almost invisible cloud of dust into the air via the power supply or case fan. It was difficult to find the source without being able to touch or move anything.

The overly sensitive Nikken AQM also created a problem. It would go tilt fairly quickly even at a fair distance from the source of smoke. I needed a smoke attenuator which was provided by restricting the air flow with a somewhat lint free rag and some duct tape.

Once the procedure was established, it was very easy to find the source of the smoke.

No. The Nikken was designed for people with allergies or health issues and may be associated with aroma-therapy which is hinted in the terse manual. A look at their web pile will show their intended audience. It is NOT a precision instrument. My guess(tm) is that it is simply looking for large particles, which comprise most of the lung irritants.

Photos:

The hole in the intake nozzle is for the translucent tube that feeds the intake of the light box.

CAM-003 Light box:

PCB. Note the two push buttons and about 5 pots:

Exhaust fan:

View from the exhaust end: The metal plate in the middle is floating and not connected to the other sheet metal. My guess(tm) is that it's a static brush, intended to strip off any charge from the dust particles that might cause them to stick to the metal duct walls.

Serial number sticker:

I dumped 3 PDF files into the above directory which are scans of the English language parts of the user manual.