The second temperature threshold T2 may be {TAIL ~ a temperature} above which the catalysts in {HEAD ~ the emission control device} may begin to degrade 
The second temperature threshold T2 may be { TAIL ~ a temperature } above which the catalysts in { HEAD ~ the emission control device } may begin to degrade
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH