It’s long been known that weather can have a real effect on our mood and morale. Rainy days, for example, are often associated with sadness, while sunny days tend to bring a smile to the face. On the other hand, extreme temperatures – particularly hot spells – tend to increase stress and aggression.

But weather isn’t the only atmospheric factor that could have an impact on our mood: a new study published in the journal Plos One suggests that pollution may also produce similar effects.

Researcher Michelle Ng and her team at Stanford University studied the known associations between exposure to air pollution and adverse effects on mental health. Their study proposes a new concept, that of “affective sensitivity to air pollution”, which they (funnily enough) refer to using the acronym “Asap”.

Asap, in this context, refers to the fluctuation of an individual’s affective states – that is, the underlying experience of feeling, emotion, attachment, or mood – according to the different levels of air pollution to which they are exposed on a daily basis.

For their research, the experts used statistical models and data obtained from 150 Americans over a period of more than a year. The scientists studied these models to determine to what extent and in what way air quality could affect the mood (negatively or positively) and alertness of people living in the same county in the US.

Their findings show that individuals’ state of alertness tends to be lower than usual on days when air pollution is higher. The researchers also note that “affective sensitivity to air pollution is likely to vary greatly between individuals”.

“Asap could help partially explain one of the mechanisms by which exposure to air pollution increases longer-term risk for adverse mental health outcomes, like symptoms of anxiety and depression, found in prior research,” the scientists noted.

In light of these findings, the authors stress the need to better integrate affect into climate adaptation policies, plans and programmes; for example by developing strategies to safeguard people’s mental health.

The researchers also warn that if air pollution disrupts an individual’s “affect”, this could translate into a lack of protective climate action.

“For example, if affect is blunted due to wildfire-induced air pollution, these individuals may take fewer adaptation behaviours in response to both air pollution and heat waves, with serious implications for their wellbeing,” they outlined.

And they stress the urgency by highlighting that “90% of the population worldwide, especially communities of colour and low-income communities, breathes air that does not meet the World Health Organization’s guidelines for livable air quality”.