Any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions. It has been EPA's policy that organic compounds with a negligible level of reactivity need not be regulated to reduce ozone. The EPA determines whether a given organic compound has "negligible" reactivity by comparing the compound's reactivity to the reactivity of ethane. The EPA lists these compounds in its regulations (at 40 CFR 51.100(s)) and excludes them from the definition of VOC. The chemicals on this list are often called "negligibly reactive" organic compounds.