2017 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5222771/ Jhun, Iny North America Observational Students Elementary (K-5) Respiratory symptoms Asthma Indoor air quality Environmental intervention Baseline classroom levels of fine particulate matter (particulate matter with diameter of <2.5 μm [PM2.5]) and black carbon (BC) were 6.3 and 0.41 μg/m3, respectively. When comparing the intervention to the control group, classroom PM2.5 levels were reduced by 49% and 42% and BC levels were reduced by 58% and 55% in the first and second follow-up periods, respectively (P < .05 for all comparisons). When comparing the children randomized to intervention and control classrooms, there was a modest improvement in peak flow, but no significant changes in forced expiratory volume in 1 second (FEV1) and asthma symptoms.