
The dirtier the air, the more people spend?
Sanghwa Kim of McMaster University and Michael Trusov of the University of Maryland took credit card data from residents of Seoul, more than four million transactions over two years, and matched it against the daily air quality index.
And the link did show up: when the AQI rises by 100 units, a person's average daily spending goes up by about 2.45%. And people don't start buying more often - the amount per purchase grows instead. They don't spend more times, they spend more per time.
The increase goes to categories with an emotional core: entertainment, leisure, cafes and restaurants. On necessities, dirty air has almost no effect. That selectivity is what led the authors to their explanation: on days that are bad for the lungs, people use a purchase as a way to fix their mood, to buy off a spoiled day.
To check that mood was really the driver, the authors ran a separate experiment: people were shown an app with either a clear or a polluted sky. Those given the smog wanted to spend more, and again on pleasures rather than on necessities. Air pollution works like a quiet nudge toward an impulsive purchase.
It's worth keeping in mind who this was measured on: the Seoul sample is skewed, mostly men aged 20 to 30, an imperfect sample for now, and we won't extrapolate it to everyone. But the direction itself held up both in the data and in the experiment.