beijing's air quality did not get worse after the olympics. (edited to clarify)
"Dangerous Any exposure to the air, even for a few minutes, can lead to serious health effects on everybody. Avoid outdoor activities." https://www.accuweather.com/en/cn/beijing/101924/air-quality...
"Very Unhealthy Health warnings of emergency conditions. The entire population is more likely to be affected." https://aqicn.org/city/beijing/
So not sure I fully believe that.
according to this report air quality in beijing continuously improved for the last few decades:
https://www.unep.org/resources/report/review-20-years-air-po...