Now that we identified the different types of filtration technology let’s discuss particle sizes a bit. Depending on the type of contaminant and the type of filtration we are using, science uses three main conventions to describe particle size.

• Micrometers or microns – 1 micron = 0.00004 inches
• Angstrom units – 1 angstrom = 10(-4) microns. Or 10,000 angstroms = 1 micron
• Molecular Weight Units – 0 – 500,000. The upper number equates to roughly 1 micron.

As you can see, the convention we use as a lot to do with what we are looking at. The micron scale applies nicely to dirt and silt, which may fall in the 2 – 10 micron range, but far too small to make sense at 0.001 microns measuring table salt dissolved in water.

We will delve more into this as we go, but for now, here are a few common contaminants rated according to their approximate size.

• Pesticide molecules are about 0.0015 microns, 12 Angstroms, or 250 molecular weight units
• Cigarette smoke is about 0.1 microns, 1,000 Angstroms, or 175,000 molecular weight units
• A grain of sand is about 200 microns, 1.5 million Angstroms, and way off the molecular weight scale

In the next part, we will match up different sized contaminants with the filtration technology that best removes them.