Japanese researchers say they have developed a smog sensor the size of a finger nail that could be carried around and used to measure pollution in the air that people breathe each day. It is significantly smaller than the sensors as big as bulky boxes that are currently used to measure smog and continuously take measurements. "In the future you could measure the pollution at the end of the day when you come home,' one researcher involved in the study at NTT Energy and Environment Systems Laboratories said.