On my first morning in Beijing, the Beijinger who met me for coffee commented, “I can’t believe what nice weather you’re getting.” I thought she was referring to the sunny day and the moderate temperature, and maybe she was. But she was also definitely referring to the air quality.
We didn’t realize how good the air quality was when we arrived until today, when the Air Quality Index (AQI) went back to “normal.” These two photos were taken at approximately the same time of day, in similar weather. 
The AQI hasn’t been bad (by Beijing standards) but we feel it. Wearing contacts is slightly uncomfortable; Wes has developed a dry cough.
People sometimes use smog as a metaphor for, say, systemic racism in the U.S, but I haven’t actually been in really serious smog since the days of my childhood in Southern Cal when we had “air alert” days that kept us from going out to the playground. Smog sucks. It’s microscopic. It’s everywhere. You get used to it.
(The first photo is of the large lake at the Summer Palace — the “Versailles” of Beijing).