Air pollution is not just bad for health also makes people unhappy, a new study has shown.

Researchers at MIT and the University of Beijing discovered a direct link between the amount of particulates in the air and happiness.

Research has previously shown that air pollution is damaging to health, cognitive performance, labor productivity, and educational outcomes.

But air pollution also has a broader impact on people's social lives and behavior, according Siqi Zheng, the Samuel Tak Lee Associate Professor in MIT's Department of Urban Studies

“Pollution also has an emotional cost,” said Dr Zheng. “People are unhappy, and that means they may make irrational decisions.”

Researchers used pollution data from 144 Chinese cities and monitored general happiness of urban dwellers by looking at the mood using 210 million messages from China's largest microblogging platform, Sina Weibo.

They found a significantly negative correlation between pollution and happiness levels, with every increase in pollution above a healthy level bringing happiness down by 0.04 points out of 100.

On Monday some parts of London recorded Air Quality Index (AQI) levels of 151, more than 100 points above healthy limits.

It suggests that people were four points unhappier than they would have been without polluted levels. For China, pollution can rise into the 700s, which could be having a major impact on happiness.