Another terminology question

["Dian R. Deevey" <diandv@taconic.net>]

I've found the term "ROC" on a list of emissions in a EIR for a Portland
cement mfg plant in California, and I'm not familiar with it.  The
rest of the list consists of just the criteria pollutants, (except for
ozone) and context analysis suggests that its a family of hydrocarbons,
present on account of contaminants in the limestone feedstock.  One
other hint as to its composition: it contributes to ozone and smog formation
in the atmosphere by secondary reactions.

Is it volatile and particulate hydrocarbons?  What does the R stand for?

Dian Deevey