Since the beginning of this year, the levels of air pollution in Beijing have been dangerously high, with thick clouds of smog chasing people indoors, disrupting air travel, and affecting the health of millions. The past two weeks have been especially bad -- at one point the pollution level measured 40 times recommended safety levels. Authorities are taking short-term measures to combat the current crisis, shutting down some factories and limiting government auto usage. However, long-term solutions seem distant, as China's use of coal continues to rise, and the government remains slow to acknowledge and address the problems. * Starting with photo #2, a four-part set of these images is interactive, allowing you to click the photo and 'clear the air', viewing a difference over time.