The decision to devalue the yuan has shaken investors, who fear a currency war and question the health of China's economy, the second-largest in the world.
Years of rapid industrial expansion have left many parts of China contending with thick smog and dirty water. The move comes at a time when China is trying to shift away from the investment-led economic model that has generated such dizzying growth in recent years, but the global economic downturn has made the transition a lot more challenging.