Hydrocarbon Units: ppmC vs ppmC3 vs ppmC6

[chingkui]

I am working on a project about pollution emission, but I am not a chemist. I am seeing the units ppmC, ppmC3 and ppmC6 almost everyday, and I have trouble understanding what they stand for. The only definition I get is "Parts per million hydrocarbon concentration expressed as methane (for ppmC)/propane (for ppmC3)/hexane (for ppmC6)". I have no trouble with the meaning of "part per million" at all, what I don't understand is whether using, for example ppmC3 means only propane concentration is measured? or is it something else? Is there a method to tell apart the methane, propane and hexane contribution to the hydrocarbon concentration? Thanks.

 

[chemisttree]

Yes, you could speciate the various hydrocarbon components in a mixture by http://www.epa.gov/eogapti1/course422/ce4b3.html. C2, C3 and C6 have a meaning within the subject area you are investigating but might mean something else in another context. It should be defined or referenced within the text of the article you are reading.