Poor air quality is a major problem worldwide. Exposure to air pollution is linked to the premature deaths of an estimated 6.5 million people every year. This makes air pollution the fourth largest threat to human health, trailing only high blood pressure, dietary risks, and smoking.
At night our planet is now bathed in artificial light, ranging from streetlights and floodlights to burning gas flares in oil fields. There are few places that are truly dark at night.