Particles per million is far better than "parts per million" or ppm!
Frank Russo - July 18, 2009.
The concentration of contaminants in water etc, should be expressed in "particles per million" rather than "parts per million". The latter is simply a weight to weight ratio, i.e. 1 gram per 1000 kilograms of water. This however is unsatisfactory as the contaminant usually acts in "units" which are variable in weight... i.e. molecular weight, atomic weight etc.
As I pointed out to the Department of Health the other week, a fluoride in the water of 1 ppm would actually contain about 10 times more particles (approximately) than lead at the same concentration, (similar reckonings would apply when compared to gold)! So one should express things in a unit that compares apples with apples rather than apples with watermelons!
I think my observation was well received!