PARIS (AFP) – Pollution from Asia is boosting levels of ozone in the skies above the western United States, a trend that could hamper US efforts to meet tougher smog standards, experts said on Wednesday. Their study focuses on data for ozone in springtime above western North America at an altitude of between three and eight kilometers (two and five miles). This height is between the stratosphere -- where a thin layer of ozone helps to filter out dangerous ultra-violet light from the Sun -- and ground level, where ozone can be a bad hazard for people with cardiac or...