This picture was taken on a day of Nov. 2019. On that day, air pollution was terrible in Beijing. For almost one week, there was no air current. Fog with air pollution got thicker and thicker. On that day, I could not bear that grey sky and studied how polluted it was. My mobile phone application read the pollution was at very formidable rank. Then, I had to wear my professional gas mask.
It is different with regular masks. It can protect human from both gas and dangerous PM 2.5. I should say, in Beijing, every year, there must be several days of thick PM 2.5 air pollution. No matter what the season is, once there were no air current for several days, then it comes.
As Beijing local people, we prefer gales. After a gale, there must be very blue sky.
Although only several days of horrible air pollution in a year in Beijing, if you want see beautiful Beijing, better to have tour after gale day, or rain day, or snow day. You must be astonished by the beautiful Beijing with blue sky background. (s)He is so beautiful!