THE DEATH TOLL

摘要

We know that nitrogen oxides (NO_x), especially the nitrogen dioxide (NO_2) discharged from car exhausts, are indirectly harmful. They contribute to the production of ozone and fine particulate matter, both of which harm human health. According to estimates by the European Environment Agency, in 2011 ozone was the cause of about 16,000 premature deaths in the European Union, and particulate matter could be attributed to around 430,000 deaths. But it has been difficult to establish whether NO_2 itself is harmful. That is changing, says Martin Williams of King's College London. "Now, there is much stronger evidence for independent effects of NO_2."