Living on the 20th floor of a high rise building isolates people from the world. Cars, streets, shaokao vendors—they’re all farther away. So does that mean PM2.5 is lower on the higher floors of buildings?
Tristan from the Smart Air team tested this by taking laser particle counters from floor 1 to floor 22 of an apartment building in Chaoyangmen, Beijing. Tristan tested on two polluted summer days. The World Health Organization’s 24-hour PM2.5 limit is 25 micrograms. Tristan measured 207 micrograms on day 1 and 84 micrograms on day 2, so these were polluted days.
Tristan brought the Air Visual Node and the Dylos DC1700 laser particle counters and took measurements at every hallway window in from floor 1 to 22 and all the even-numbered floors in between. Tests have found that the Dylos and Node correlate highly with the US Embassy PM2.5 readings (r > .90).
Results: The Small Stuff
First we looked at the smaller particles, particles 0.5 microns and above. We did the most drastic comparison: was particulate lower on the 22nd floor than the 1st floor?
On Day 1, the Dylos found small particulate was actually a bit higher on the top floor.
On Day 2, the Node found PM2.5 was about the same on the top floor.
Results were similar when we averaged floors 1-10 versus floors 12-22. Upper floors were slightly higher in one test, slightly lower on the other test.
Bottom line: There is no clear benefit of living on a high floor in small particles.
Results: Larger Particles
So there weren’t clear differences in the small particles, but what about larger particles above 2.5 microns? Perhaps this sort of dust is lower on the higher floors because it settles faster than small particles.
Again, there was no clear benefit. The 22nd floor had fewer particles on Day 1 with the Dylos:
But then the 22nd floor had more large particles on Day 2 with the Node:
But averaging floors 1-10 versus 12-22, higher floors had a slight advantage for these large particles. Higher floors had 3% fewer large particles on day 1 and 10% fewer on day 2.
Bottom line: Higher floors may have slightly fewer large particles.
So How High Up Do You Need to Be?
So living on the 22nd floor doesn’t help with the small PM2.5 particles. Then how high would you have to live to escape PM2.5? Without a helicopter to do these tests, here’s our best guess:
Air mixes to different heights in the summer and winter, in day and night. In the daytime, the lowest average mixing height is 1,000 meters, which is a lot higher than high rise buildings.
At about 3.1 meters per floor, people on the 20th floor are about 62 meters high. So that’s not going to get us anywhere near the 1,000 meter mixing height.
But at night, air is more settled. At night, the average is around 400 meters. Can we get that high?
Even if we stretch all the way up to the 30th floor, that’s still just 93 meters high. To get to 400 meters, we’d need to live on the 129th floor. For now, we earth-dwellers can’t hope to outclimb pollution.
Choon Khin is a Smart Air engineer from Singapore, studying chemical engineering at the National University of Singapore