In short, it is difficult to control both the filter temperature and the concentration of nitrogen dioxide in {TAIL ~ the filter} to {HEAD ~ optimum values} simultaneously 
In short , it is difficult to control both the filter temperature and the concentration of nitrogen dioxide in { TAIL ~ the filter } to { HEAD ~ optimum values } simultaneously
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH