2017 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5340641/ Gaffin, Jonathan M North America Observational Asthma Black carbon Exposure modeling Particulate matter (PM) Fine particulate matter (PM 2.5) School Sufur tracer method Mixed effects regression models found significant random intercept and slope effects, which indicate that: (1) there are important PM2.5 sources in classrooms; (2) the penetration of outdoor PM2.5 particles varies by school and (3) the site-specific outside PM2.5 levels (inferred by the models) differ from those observed at the central monitor site. Similar results were found for BC except for lack of indoor sources. The fitted predictions from the sulfur-adjusted models were moderately predictive of observed indoor pollutant levels (out of sample correlations: PM2.5: r2=0.68, BC; r2=0.61).