The DOC 32 oxidizes {TAIL ~ the exhaust} based on {HEAD ~ the post combustion air/fuel ratio} 
The DOC 32 oxidizes { TAIL ~ the exhaust } based on { HEAD ~ the post combustion air / fuel ratio }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD