At this point, {HEAD ~ diesel exhaust emissions B} are also being treated for {TAIL ~ nitrogen oxide contaminants} 
are treated for
At this point , { HEAD ~ diesel exhaust emissions B } are also being treated for { TAIL ~ nitrogen oxide contaminants }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL