There is a multiplying list of concerns when it comes to the environment. With deforestation, climate change and ocean plastic (to name but a few issues), it’s difficult to know which topic to wring one’s hands over at any given time. One problem in the ascendency is air pollution in cities. It’s a sign of the times: our transgressions against nature aren’t just being felt by squirrels and sea turtles but by residents in wealthy, cosmopolitan capitals too. While the physical risk of living in some built-up areas equates to smoking a packet of cigarettes every day for 29 years, there is another, subtler problem.According to new findings by scientists, published today in research journal Plos Biology, bad air could be associated with higher cases of mental illnesses, such as bipolar disorder and depression. Examining populations across the US and Denmark, the study found that exposure to polluted air during the first 10 years of a person’s life – particularly in Denmark – leads to a twofold increase in schizophrenia and personality disorders. While the results have stirred controversy in the scientific community, the findings ought to add momentum to the drive to clean up the air in cities. Jakarta’s move (see below) is the right response and it’s this simple: more plants, fewer cars.