{TAIL ~ Nitrogen dioxide gas} is sensed in accordance with a color change before and after the sensor element is exposed to air to be measured for {HEAD ~ a predetermined time} 
{ TAIL ~ Nitrogen dioxide gas } is sensed in accordance with a color change before and after the sensor element is exposed to air to be measured for { HEAD ~ a predetermined time }
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD