Baby Claire, an acronym for Clean Air for Everyone, is silent because she is a doll and wedged beside her are three electric sensors that measure the particulate matter that spews out of factories and car exhausts. Her minders, though dressed for a trek, will walk 7.5 kilometres (4.5 miles) -- about 10,000 steps -- from the Antwerp University campus through Belgium's notorious traffic, which makes this small EU country of 11 million one of the most harmful polluters in Europe. Referred to as the "silent killer", air pollution is responsible for about seven million premature deaths worldwide each year, according to the UN.