2018 Yes https://www.sciencedirect.com/science/article/abs/pii/S0048969717333326?via%3Dihub Villanueva, Florentina Europe Exposure Study Modeling Elementary (K-5) Volatile Organic Compounds (VOCs) Nitrogen Dioxide (NO2) Volatile organic compounds (VOCs) Carbonyl compounds Nitrogen dioxide (NO2) Indoor air quality School Spain . The most abundant pollutants at schools were the aldehydes formaldehyde and hexanal. After carbonyls, n-dodecane was the most abundant compound in the study areas. The NO2 concentrations were higher in the urban area, followed by industrial area and rural areas. For benzene, its concentration in the industrial area was significantly higher than in the urban and rural areas which reflects the magnitude of the contribution to the indoor air by petrochemical plant during the sampling period. Principal component analysis, indoor/outdoor ratios, multiple linear regressions and Spearman correlation coefficients were used to investigate the origin, the indoor pollutant determinants and to establish common sources between VOCs and NO2. Seven components were extracted from the application of PCA to the indoor measurements accounting for 77.5% of the total variance. The analysis of indoor/outdoor ratios and correlations demonstrated that sources in the indoor environment are prevailing for most of the investigated VOCs. Benzene and n-pentane have a major relevance as outdoor sources, while aldehydes, terpenes, alkanes and most aromatic hydrocarbons as indoor sources. For NO2, ethylbenzene and toluene both indoor and outdoor sources probably contributed to the measured concentrations.