A desulphurization event includes operating one or more emission control devices at an elevated temperature and with a selected air fuel ratio to reduce {HEAD ~ contamination}, such as sulphur and {TAIL ~ other contaminants} 
such as
A desulphurization event includes operating one or more emission control devices at an elevated temperature and with a selected air fuel ratio to reduce { HEAD ~ contamination } , such as sulphur and { TAIL ~ other contaminants }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL