Crime : it's all in your breath

I've heard of the lead-crime hypothesis before, but this seems to be more general.

 The most polluted days correlated with the worst test scores. On days where the air quality was cleanest, students performed better. “We could see a clear decline [of performance] on days that were more highly polluted,” says Roth. “Even a few days before and a few days after, we found no effect – it’s really just on the day of the exam that the test score decreased significantly.” 

In 2018 research his team analysed two years of crime data from over 600 of London’s electoral wards, and found that more petty crimes occurred on the most polluted days, in both rich and poor areas. It's important to note that this finding is purely correlational – but Roth has reason to believe that there is a causal link. 

His team also compared very specific areas over time, as well as following levels of pollution over time. A cloud of polluted air, after all, can move around depending which direction the wind blows. This takes pollution to different parts of the city, at random, to both richer and poorer areas. “We just followed this cloud on a daily level and see what happened to crime in areas when the cloud arrives… We found that wherever it goes crime rate increases,” he explains.

Importantly, even moderate pollution made a difference. “We find that these large effects on crime are present at levels which are well below current regulatory standards.” In other words, levels that the US Environmental Protection Agency classifies as “good” were still strongly linked with higher crime rates.

The most obvious question is how much does air pollution drive crime. The BBC article doesn't say, but it provides a direct link to one which does. And it's not small.

The researchers found that a 10 point rise of the air pollution measure, the Air Quality Index (AQI), increases the crime rate by 0.9 per cent. This means that the crime rate in London is 8.4 per cent higher on the most polluted day (AQI 103.6) compared to the days with the lowest level of pollution (AQI =9.3).

That seems too strong to ignore. At the same time, it's far too small to blame all crime on air pollution. But chemicals which impair reasoning and judgement that push the criminally-inclined over the edge ? That I can believe. Pollution would seem to be an important contributing factor, but no more or less than that. Naively, the short timescale argues in favour of a direct causal connection but I'd be interesting in alternative interpretations.

How air pollution is doing more than killing us

In the future, police and crime prevention units may begin to monitor the levels of pollution in their cities, and deploy resources to the areas where pollution is heaviest on a given day. This may sound like the plot of a science fiction movie, but recent findings suggest that this may well be a worthwhile practice.