One of you PMed me about this, and so I'll write here my response to him:

There are a couple of things you need to understand. These ultrafine particles that come out of a diesel engine won't be completely filtered by any mask. HEPA filters are pretty good for any particle over a micron in diameter. But when you get to particles under half a micron, it is difficult to filter them out. Diesel exhaust has a lot of components. See this article:

http://www.cdc.gov/elcosh/docs/d060...09/d000609.html

Filtering most of these out is better much better for you than simply breathing them in. The mask I use is a North half-face respirator, #7700-30L (for Large). I use it with the cartridge for HEPA filtration, #DOP12H4. They also make a much larger cartridge which is a combination of an Organic Vapor and HEPA filter, and it costs about $8 for a set of two cartridges (I used them with a full-face respirator when I was pouring solvent chemicals from our process lab into a large drum for hazardous waste disposal. Here's North's website for this mask:

http://www.northsafety.com/usa/en/bs....html?GID=3788

Here is the filter which will get just about anything that a diesel exhaust engine can send your way (except the ultra-fine particles):

http://www.northsafety.com/usa/en/bs....html?GID=3766

But I am using this cartridge, as I am mainly interested in the HEPA filtration of particles:

http://www.northsafety.com/usa/en/bs....html?GID=3763

You can get these at Safety Supply stores (see your local listings), or look on-line at:

http://www.labsafety.com/search/defa...8&Nu=dept%5Fid

How do drivers react? Well, I used them for awhile last year, without much reaction that I saw at all.

How do I react? They were warmer, and my glasses did not fog up much when using them.

Why aren't I using it now? Well, we've had 38 or so days with only one or two without measureable rain, so the pollution levels are low here. I do hold my breath when a bus comes by, and if I see diesel exhaust ahead of me, I have at times stopped and waited for it to dissipate before entering the area where it was. So far, that strategy seems to be holding up pretty well.

Next spring and summer, if the pollution levels go up, I'll again be wearing the mask.

John

PS--for some reason the links didn't work, and I have now tried replacing them (they could not be copied). Here is the home site if this doesn't work:

http://www.northsafety.com/bs_splash.html?PAGEID=10836