I'm of an age where I remember riding in a car past Tacoma, Washington and watching pitch black smoke pour into the sky from smokestacks. I remember particulate matter fall from the sky from the papermill in our town. Each parking lot had a car wash to drive thru on your way home from work.
As a country we fixed all that.
Why is China figuring this all our decades later?
"Giant digital billboard screens in Beijing have recently been used to display sunrises on mornings when the city’s air pollution is so severe that it blots out the rising sun. These photos were taken on January 16, 2014, when PM2.5 particulate air pollution spiked to 671 micrograms per cubic meter—the World Health Organization considers 25 micrograms to be the maximum safe level. "