The standard indicators are as follows : “ NO ” ( not occurring ) for emissions by sources and removals by sinks of greenhouse gases that do not occur for a particular gas or source/sink category within a country ; “ NE ” ( not estimated ) for existing emissions by sources and removals by sinks of greenhouse gases which have not been estimated . Where “ NE ” is used in an inventory for emissions or removals of CO2 , N2O , CH4 , HFCs , PFCs , or SF6 , the Party should indicate , using the completeness table of the common reporting format , why emissions could not be estimated ;