NASA’s Goddard Space Flight Center has posted a gallery of satellite measurements of nitrogen dioxide, taken by the Aura spacecraft. The results show a clear, nation-wide decline in this type of air pollution from 2005 to 2011. There are a lot of contributing factors for the reduction. This period includes the beginning of the Great Recession. It also appears that in 2005, the United States entered a period of declining automobile use that seems to be unrelated to gas prices or the overall economy. Cars and trucks have also gotten cleaner and more efficient, thanks to consumer demand and regulations. Nitrogen dioxide emissions from American coal-fired power plants roughly halved, from almost four million short tons 2005, to less than two million in 2011.
Air pollution is still an enormous problem, but it looks like steady progress is being made.
It would be interesting to see this data for China. See, for example, the shockingly titled Energy Information Administration report, “China produces and consumes almost as much coal as the rest of the world combined.”