The month of December was depressing, not just because it was cold, but also because the sky was gray from air pollution almost every single day. It is the worst feeling going outside and never seeing the sun. The smog is especially bad in winter due to an accumulation of fine particles from burning wood and coal, car emissions, etc. I took a picture of the sky from my balcony most afternoons in December. The numbers are the Air Quality Index sourced from the World Air Quality Index. To put it in perspective, southern California which has the worst pollution in America has bad air days around 90. It has been found that emissions from China cross the Pacific Ocean and contribute to air pollution in the Western United States.