A reasonable way to get some consistent test results, is to compare the results of tests from folk already living in areas of higher concentration in the air, with folk in rural ereas where concentration is less. This stuff wont' float around undispersed very far beyone the borders of cities, it is a kind of inert particulate, it won't react with the atmosphere in the way that pollution from combustion does, to launch itself upwards into the atmosphere, it has to settle mostly around towns, cities, and major highways, where most of it is generated on roads. Also it is probably possible to create test systems that test for the presence of this in the air, like we do for other particulates. Could do with some references to your sources of information on this subject, Will.