BEIJING, Jan. 27 (Xinhua) -- Researchers have disclosed that air quality affects people's emotional expressions on social media.

They collected and analyzed 210 million geotagged tweets on Sina Weibo across China's 144 cities from March to November in 2014 and constructed a daily city-level expressed happiness metric based on the sentiment.

The researchers compared the PM2.5 concentrations with the mood index and found that the two numbers were inversely related.

According to the study published in the journal of Nature Human Behavior, the researchers examined questions like: Does air pollution affect a citizen's expressed happiness in real time? Do the effects of pollution on happiness vary on different days such as weekends, holidays and very hot days? And whether different population groups are affected by air pollution?

They found that people suffer more on weekends, holidays and days with extreme weather conditions. The expressed happiness of women, high-income people and the residents of both the cleanest and dirtiest cities are more sensitive to air pollution.