Every year, 7 million people die from an airborne pollutant known as particulate matter. It’s not something that many of us think about, myself included. But on a recent trip to Tanzania I came face to face with this silent killer.

A Masai family whom we visited used a small wood fire as their only source of warmth, cooking and light for their small hut. This may sound quaint to some, but the indoor air pollution this creates is quite deadly.