text: Many environmental protection agencies have issued regulations that limit the concentration of pollutants in gaseous emissions and define the reference conditions applicable to those concentration limits.  For example, such a regulation might limit the concentration of NOx to 55 ppmv in a dry combustion exhaust gas corrected to 3 volume percent O.  As another example, a regulation might limit the concentration of particulate matter to 0.1 grain per standard cubic foot (i.e., scf) of dry exhaust gas corrected to 12 volume percent CO.
  Environmental agencies in the USA often denote a standard cubic foot of dry gas as "dscf" or as "scfd".  Likewise, a standard cubic meter of dry gas is often denoted as "dscm" or "scmd" (again, by environmental agencies in the USA).