Researchers are using a new measurement to show how a person’s mood or affect fluctuates with daily changes in air pollution. 

A new study highlights the concept of ‘Affective Sensitivity to Air Pollution’ (ASAP).

The study by Michelle Ng and colleagues at Stanford University demonstrates that people have varying levels of sensitivity to air pollution, which can affect their daily affective states differently.

Using data collected over more than a year from 150 individuals in the United States, the researchers applied statistical models to evaluate how daily outdoor air pollution levels, as measured by local air quality monitors, influence the two components of affective state: arousal (the level of physiological activation) and valence (the positivity or negativity of mood). 

They found that higher-than-usual air pollution levels were associated with lower arousal, indicating that people felt less alert or engaged on such days. 

Importantly, there were significant individual differences in how much air pollution affected each person's mood.

These findings suggest that ASAP could explain why exposure to air pollution is linked to longer-term mental health issues, such as anxiety and depression. 

Additionally, if air pollution dampens a person's affect, this could contribute to a lack of motivation for climate action. 

The researchers propose that ASAP could be used in climate adaptation strategies to better integrate mental health considerations, such as personalising interventions to support individuals who are particularly sensitive to air pollution.