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