Grist: When planning a recent trip to Beijing, I was delighted to see that the forecast predicted perfect weather: sunny, clear, highs in the 70s with no chance of rain. So imagine my surprise when on my first morning in the city I looked out the window and saw a dense, immobile ceiling of dark gray clouds.
It wasnt that Weather.com got it wrong. It was that pollution was unusually high that day - the U.S. Embassy Air Quality Index (AQI) readings were over 400 parts per million of PM2.5, well into the...