High pollution linked to unhappiness among Chinese people, MIT researchers say

As London industrialized in the 19th and 20th centuries, it produced fog—a lot of it. On particularly bad days, London was choked with a thick, yellow-green gas that could kill, making for a fairly miserable climate. So much so, poet and playwright Oscar Wilde once said, “London is too full of fogs and serious people. Whether the fogs produce the serious people, or whether the serious people produce the fogs, I don’t know, but the whole thing rather gets on my nerves.”

Now, MIT researcher Siqi Zheng may have an answer for Oscar Wilde: air pollution does actually make people more or serious, or at least less happy. But London’s air has improved over the years — instead, Zheng looked at China, one of the foggier spots on 21^st-century Earth.

Prior studies have looked at self-reports of people’s happiness and compared them with air pollution, but these reflections occur after pollution peaks and tend to reflect people’s overall happiness. Zheng and colleagues wondered if there was a better way to determine how much pollution impacted happiness in the moment. Fortunately, human beings love to talk about themselves. Today, people’s self-expression happens the most on social media programs, so Zheng turned to Sina Weibo, China’s version of Twitter. This turned out to be a very rich source of data — Zheng’s sample size consisted of 33 million posts from 589,000 users.

Measuring pollution was a fairly straightforward task. China’s Ministry of Environmental Protection releases a daily Air Quality Index, or AQI, which measures the main pollutants in each city. In addition to looking at the AQI, Zheng also focused on a class of pollutants that the Chinese are particularly concerned about, PM_2.5. (or particulate matter smaller than 2.5 micrograms) has been the most common form of pollutant in China in recent years, and its small size enables the particles to stay in the air longer and bypass the nose or even masks to enter the body and contribute to disease and poor health outcomes.

However, matching air pollution to sentiment was slightly more difficult. It obviously would have been too much work to go through 33 million posts and assess whether they express happiness or not. Fortunately, machine-learning algorithms are able to sift through huge amounts of text, process people’s language, and spit out a measurement of how much happiness each post expressed. Zheng and colleagues used a happiness index on a scale of 0 to 100 to quantify the posts’ average happiness and used each posts’ geotag to match it to local areas with high or low pollution. What’s more, they used two different machine-learning algorithms to compare the measurements and ensure that their results weren’t simply because of some flaw in their algorithm.

These two charts show a) the density and distribution of Sina Weibo posts used in the study and b) the relationship between overall happiness and the level of PM2.5 on a given day. Image source: Zheng et al., 2019

What they found should come as no surprise. There was a significant negative correlation between happiness and pollution. The results, however, became a bit more nuanced as they dove deeper. Women tended to be unhappier on high-pollution days than men. And, when a high-pollution day fell on a weekend or a holiday, Sina Weibo posts expressed much more unhappiness. After all, having to cancel your social plans because of high pollution isn’t likely to put a smile on your face.

In China, pollution causes 1.1 million people to die prematurely each year and costs their economy $38 billion. Despite this loss, China keeps chugging along, growing at an astounding 8 percent per year. But this growth doesn’t seem to really be making people happy. It produces pollution, significantly impacting people’s quality of life. And, when people are miserable, they tend to act irrationally. Prior research had suggested that people act out in impulsive and risky ways on high-pollution days. Hopefully, research such as Zheng’s will give the Chinese government some impetus to reduce pollution: if not to make people’s lives better, then to prevent the high costs associated with high pollution.