Within the framework of the French national research program PRIMEQUAL, measurementsof outdoor and indoor pollution have been carried out in eight schools of La Rochelle (France)and its suburbs. The buildings were naturally ventilated by opening the windows ormechanically ventilated, and showed various air permeabilities. Ozone, nitrogen oxides (NOand NO2), and particles (15 size intervals ranging from 0.3 to 15 m) concentrations werecontinuously monitored indoors and outdoors for two 2-week periods. The indoor humidity,temperature, CO2 concentration (occupancy), window opening and building permeability werealso measured. The paper deals with a statistical analysis of the data aimed at identifying theparameters influencing the compared outdoor and indoor pollution levels. After a briefdescription of the experimental data, the results of the principal component analyses (PCA)are discussed by referring to the likely underlying physical processes involved. The mainconclusions arising from the study are: (1) the influence of occupancy on indoor particleconcentrations varies as a function of the particles size; (2) the building permeability greatlyinfluences the indoor/outdoor concentrations ratio for ozone and (3) the method enables one toidentify the cases where nitrogen oxides are emitted indoors.