We conducted large-scale lost letter experiments in Beijing, a megacity with more than 21 million residents, to test if the observed altruistic attribute of the letter recipient would induce more passersby to return the lost letters. The treatment letters were addressed to a nationally renowned...

We conducted a large-scale lost letter experiment with a novel design across all seasons in Beijing to study whether ambient air pollution influences helping behavior. We assessed air pollution by PM2.5 and PM10. Our novel design allowed us to collect real-time granular data from the streets. To...