In trying to research the various air pollutants in order to write effectively about a long air quality study about to be released, I’ve been able to find lots of good information about nitrogen oxides and sulphur oxides, among others. (The EPA site has some good fact sheets about their causes and effects), but little about elemental carbon (EC) and organic carbon (OC), beyond the following:
“EC is released directly from the incomplete combustion of fossil fuels and biomass while OC, an aggregate of hudreds of individual compounds spanning a wide range of chemical and thermodynamic properties, is formed by a variety of processes, including combustion and secondary organic carbon formation.”
Are EC and OC different in chemical structure or effects? Are they different isotopes? Are they identical substances, and Is the distinction only in the method of their formation?
My take on this is that EC is the, well, elemental form of carbon. This would be pure (or probably near pure) C. I would expect this to be in form of small particles of graphite.
OC seems to be a complex mix of many different organic compounds. I would expect these to be some combination of hydrocarbons and oxygenated hydrocarbons (alcohols, esters, ethers, organic acids, etc.). These would probably be very small droplets of liquid.
This is what I think they are saying based on your quote.
Elemental carbon is particles of graphite or amorphous carbon. “Organic carbon” is the carbon content of organic molecules, which contain carbon, hydrogen, and oxygen as a rule, often with nitrogen or sulfur bonded in as well.
In other words, there’s an amount of carbon as a substance, and another amount of various substances containing carbon as a constituent element.