I’ve posted data before showing that outdoor air quality is strongly correlated with indoor particle counts (r = .71), but Chinese New Year gives nerds like me a great chance to see what happens when we get a momentary shock to air quality.
The media made a big deal about people cutting back on fireworks this year out of a concern for air quality, and that may be true, but you can still see a strong spike in PM2.5 as Beijingers rang in the year of the horse:
Not all that surprising. But what’s more interesting is that you can see a corresponding increase in the particle counts in my collaborator Gus’s bedroom (blue line):
These indoor counts are without a purifier running, so they demonstrate how quickly outdoor air pollution can find its way indoors and how variable indoor air quality can be in a single room over time. Simply put: the worse the air is outside, the worse it is inside.
Yet the glass half empty can also be half full. When outdoor particulate goes down, indoor particulate can go down in a hurry. Check out what happened after the firework apocalypse ended:
A note for fellow nerds: The indoor particle counts are not precisely on the hours, which might exaggerate the apparent time lag between indoor and outdoor counts.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.