I was in Beijing for Chinese New Year for a couple weeks in 2009, and when I flew in, I couldn't see the enormous city at all from the sky. It was completely hidden in a cloud of smog. There was some of the worst air quality of the year at that time from all the fireworks plus being the coldest time of year (so everyone is burning coal fires), and a ton of debris in the air from a 44 floor skyscraper that burned to the ground down the street (video: <a href="http://www.youtube.com/watch?v=6hSPFL2Zlpg" rel="nofollow">http://www.youtube.com/watch?v=6hSPFL2Zlpg</a>)<p>I never really knew what coal burning smelled like before. Even in the city it isn't allowed, but once we left and went to a smaller town outside Beijing that's when I really got it. It is the heat source for 99% of the population, plus it powers most of the factories. There were days where we were told we shouldn't be outside unless absolutely necessary (which was, since my husband had to commute to his job at Microsoft). At night if you blew your nose your tissue would be grey. If you took a shower, the water would run grey from dust wherever your skin had been exposed. Your clothes would be dusted in a thin layer of gray that never really went away. We tried to combat this by changing out of our clothes just inside the front door and putting them straight into the wash, but it never really went away.