2021 Yes https://www.sciencedirect.com/science/article/pii/S0160412021002397 Gignac, Florence Europe Exposure Study Students High School (9-12) Test Performance Air pollution Adolescents Attention Randomised control trial High school Average levels of PM2.5 and black carbon throughout the 1.5 h of experiment were 89% and 87%, respectively, lower in the classrooms with air cleaner than in the control classrooms. No differences were found in the median of HRT-SE between classrooms with cleaned air and normal air (percent change: 1.37%, 95% confidence interval: −2.81%, 5.56%). Sensitivity analyses with secondary attention outcomes resulted in similar findings.