The latest research on the health effects of air pollution have discovered a surprising finding: low levels of air pollution are actually more harmful than higher levels. This data has potentially important implications for people living in relatively “clean” cities like New York and London.
My Intuition About Air Pollution’s Health Effects
Join me for a quick thought experiment. Let’s say you could wave a magic wand and reduce PM2.5 pollution by 5 micrograms in either Chicago (where I live)…
or Beijing (where I often go).
Your goal: Save the most lives possible. Where would you put your magic wand to work?
Before you decide which city to help, it is important to understand the relationship between tiny PM2.5 particles and death. Would it look like this?
In this case, the idea is that air pollution hurts us little by little, but then the damage really starts to get bad at severe levels. This logic is implicit when people ask questions like, “How much saturated fat is safe?” Or “what’s a safe level of lead in my body?”
But maybe your intuition is different. Maybe pollution affects us in a linear way?
That makes sense to me too. In that case, each step up in air pollution hurts us the same as the step before.
Studies Find Low Levels of Air Pollution Most Harmful
As logical as those predictions are, they are wrong. Scientists analyzed the effects of PM2.5 on death, and they found that low levels actually hurt more. So they relationship looks more like this:
Or in the form of actual data, this is what it looks like. An increase in pollution from low levels does MORE damage than increases at higher levels.
If that doesn’t make you poop your pants, perhaps you’re not such a stats nerd like me. But here’s why that graph is crazy.
Let’s say China has a bad year, and air pollution goes from 125 to 150 micrograms. Based on China’s population, that would mean 60,000 more people will die.
That’s a lot of people, probably more than have died on “The Walking Dead.”
But that same increase—25 micrograms—would kill almost twice as many people (per capita) if it happened in China’s cleanest major city, Shenzhen.
Of course, higher levels of air pollution kill more people than lower levels overall. But more of that harm comes from the low levels of air pollution. In other words, cutting pollution in half would fail to cut deaths in half.
Why would low levels matter more?
Here’s a metaphor: imagine getting hit by a baseball bat.
That first hit would hurt a lot—probably break some bones. But what about the fifth strike? The tenth strike? A lot of the damage has already been done, so the tenth strike doesn’t add much. (Sorry for the gruesome metaphor!)
Two Reasons Why This All Matters
Besides being a surprising finding, this data has two real-world implications.
1. The most important progress is still ahead
I lived through a year of Beijing smog when the average was over 100 micrograms. In 2018, Beijing averaged about 50 micrograms.
That’s amazing progress! Beijing cut its PM2.5 by an astounding 50 micrograms.
But because of the baseball bat principle, Beijing would save more lives if they improved from here. Oddly enough, improvement becomes more valuable once things are pretty clean.
2. If you’re in a “safe” city like I am, you should be worried
For my day-job, I live in Chicago. When I see graphs like this, I feel pretty good about myself. I feel safe.
But the new studies on health effects at low levels of pollution have changed the way I think about safe air. The baseball bat principle could explain why recent studies have been finding meaningful health effects on blood pressure and diabetes.
Data has even found meaningful effects comparing 12 micrograms to 7 micrograms. Less is better.
Bottom Line: Low levels of pollution are a problem
Pollution isn’t just a Delhi or Beijing problem. People in “clean” cities like where I live should be worried too.
P.S. As scary as that data is, the data on the effectiveness on purifiers and masks is scary good. I cover that data and the three simple, low-cost things I do that drastically reduce the amount of pollution I breathe when I’m in Beijing and Delhi.
How I Protect Myself
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