Smog is a big problem in many of the world’s largest cities, especially in the massive urban agglomerations that pepper Asia. That’s why a group of researchers from Australia and China have developed a new method of detecting nitrogen dioxide in the air, which is a major contributor to smog in these cities, and causes some serious health issues. Using a new kind of sensor, smartphones could be transformed into portable air-scanners that can detect when there are unhealthy levels of nitrogen dioxide in the air.