The haze now engulfing Sydney isn't an isolated problem. Cities around the world struggle to manage the many sources of tiny airborne particles and the discomfort and illnesses these cause.
We have developed an online tool to help authorities identify which areas they should focus on for reducing forest fires and haze in order to maximize overall health benefits.
US national parks protect some of America's most spectacular outdoor settings. But new research shows that ozone pollution levels in the parks are roughly as bad as in major cities.