"Air pollution killing tens of thousands each year"

 "We have this new problem that we cannot see: it is tiny particles of nitrogen dioxide."  Professor Frank Kelly, Kings College London - as reported in the Independent.

http://www.independent.co.uk/life-style/health-and-families/health-news/air-pollution-killing-tens-of-thousands-each-year-2305992.html

This will come as a surprise to scientists who have previously thought that nitrogen dioxide is a gas.