We probably didn't need a scientific study to tell us that pollution bums people out, but we now have such a study nevertheless.
The report by S. Zheng et al., "Air Pollution Lowers Chinese Urbanites Expressed Happiness on Social Media" Nature Human Behaviour 2019, analyzes self-reported social-media data and concludes that the higher the pollution level, the lower the happiness level.
The researchers found that people are more bummed out by pollution on weekends and holidays than on work days. People are also more bummed out by pollution on cloudy days than on sunny ones, and on days that are too hot or too cold. Women tend to get more bummed out than men about pollution.
Read the full report here.