What I want to do

See if I can't see PM10 or even PM2.5 particles on a consumer scanner. I purchased a Canon canoscan 9000F MK II, which allegedly does 9600dpi, or interpolated 192000 dpi.

My attempt and results

Sticky pad prep

Using packing tape (probably polypropylene with acrylic adhesive) I made a quick sticky pad and left it out for 30 hours near my window. following the sticky pad method) I covered it in plastic wrap labeled PVC and BPA free, which means its probably LDPE. I got a lot of bubbles and wrinkles trapped, which was bad. Better technique would help, but this seems to be a bit of an issue for getting good sticky pad readings. I might go to a shellac instead.

Scanning

Then I went to scan the sticky pad, first in visible light to determine particle size, and then hopefully with polarized light later on a modified scanner. The scanning experience was underwhelming.

despite its advertised 9600dpi resolution, the scanner can't even fake it-- it crashes the software to select more than 4800dpi. After running around support websites, installing different Canon software packages, and a good measure of cursing those who build the TWAIN specification into software on consumer scanners (commercial scanners don't need drivers), I discovered a link suggesting my work might all be futile anyways. The effective resolution, according to these testers, is about 1700dpi, not the 9600 advertised.

I gave up and just played with the 4800dpi image.

Image Processing

the raw image made it hard to zoom in and look at dust:

But pull the contrast severely, and the particles start to pop right out:

Still, its hard to actually make out very small particles. On a 4800dpi scan, each pixel is about 5.3µm across. In the image below one can barely make out two dots of particles that from their pixel dimensions are 15-30µm across. If the effective resolution is 1700dpi, then the actual image pixels don't get smaller than 15µm, or 3x3 4800dpi pixels. This test seems to confirm the results from Patrick Wagner at Scan Dig, that I mentioned earlier, and the effective resolution of 1700dpi. Bummer.

Questions and next steps

So much for getting pm 2.5 measurements on a stock consumer scanner. That is pretty disappointing. I learned more about scanner resolution generally, and have some leads on slide scanners that have an effective resolution of 3300dpi that ought to have a chance of picking up PM10, but it looks like PM2.5 is out of the range of any scanner currently on the consumer/entry level professional market.

At this point, my choice is to switch optical instruments, lower my standards to PM 10, or build my own instrument. I'm still pretty keen on the latter option. Having built several projectors before I'm confident in the ability of hacked-together optics to get good results, and there are a whole century of well made lenses on Ebay for cheap because they don't fit new stuff.

Back to the drawing board...