Yes - for once the headline seems to have
undersold the results.
Reading the title, I was expecting this to be a long-term relationship, and to happen at extremely high levels of air pollution. Particularly since the study on China last year showing that exposure to PM2.5 has lasting cognitive effects, which found variation at levels far higher than anything found in the US. And ozone at approved levels (but not PM2.5) has been linked to long-term cognitive decline.
Instead, this is claiming day-to-day variation based on that PM2.5 levels that are 25% of the EPA 24-hour exposure threshold, and even below the annual EPA standard. If you told me that air pollution below the EPA safe thresholds had a noticeable impact on cancer or emphysema rates, I wouldn't be surprised at all. But this is wild - a 5% increase in violent crime based on a day of pollution! For reference, one violent crime study I just checked finds that violent crime is about 10% higher in the summer than the winter in a cold city, and late-night crime (past midnight) is about 5% higher on weekends than weekdays. So 15 micrograms of PM2.5 is about as impactful as "people stay up late and get drunk on weekends".
It's an effect so bizarrely strong that my first reaction is to assume the study is bad or confounded. Except... all the obvious patterns don't work, and the controls look solid. Unpleasant weather keeps people inside and reduces (outdoor) crime. Shared causes like high human activity should have raised property crime rates. The effect looks stable across all kinds of temperature and crime subsets. If there is a confounder, it's presumably something strong and interesting.
> Pollution levels can easily rise by much more than that.
Very true, although I note that the effect doesn't seem to continue across the whole range studied. I wonder why effect falls off, and what happens in places that are always this polluted?