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