At a recent TEDx talk, Beth Gardiner, an American journalist based in London, offered a dire message: "The air we're breathing here in London is literally killing us," she told the audience. "And it's not just London – all of Britain and much of Europe is in the midst of an invisible public health crisis."

Gardiner's warning was the result of four years of research on air pollution and its negative effects that took her across countries and continents. Her findings were recently published in her book, "Choked", which examines air pollution in various nations and the measures governments are taking to counteract it.

Read more at US News.