Indoor and outdoor PM mass and number concentrations at schools in the Athens area

Simultaneous indoor and outdoor PM₁₀ and PM₂.₅ concentration measurements were conducted in seven primary schools in the Athens area. Both gravimetric samplers and continuous monitors were used. Filters were subsequently analyzed for anion species. Moreover ultrafine particles number concentration was monitored continuously indoors and outdoors. Mean 8-hr PM₁₀ concentration was measured equal to 229 ± 182 μg/m³ indoors and 166 ± 133 μg/m³ outdoors. The respective PM₂.₅ concentrations were 82 ± 56 μg/m³ indoors and 56 ± 26 μg/m³ outdoors. Ultrafine particles 8-h mean number concentration was measured equal to 24,000 ± 17,900 particles/cm³ indoors and 32,000 ± 14,200 particles/cm³ outdoors. PM₁₀ outdoor concentrations exhibited a greater spatial variability than the corresponding PM₂.₅ ones. I/O ratios were close or above 1.00 for PM₁₀ and PM₂.₅ and smaller than 1.00 for ultrafine particles. Very high I/O ratios were observed when intense activities took place. The initial results of the chemical analysis showed that [graphic removed] accounts for the 6.6 ± 3.5% of the PM₁₀ and [graphic removed] for the 3.1 ± 1.4%.The corresponding results for PM₂.₅ are 12.0 ± 7.7% for [graphic removed] and 3.1 ± 1.9% for [graphic removed] . PM₂.₅ [graphic removed] indoor concentrations were highly correlated with outdoor ones and the regression line had the largest slope and a very low intercept, indicative of no indoor sources of fine particulate [graphic removed] . The results of the statistical analysis of indoor and outdoor concentration data support the use of [graphic removed] as a proper surrogate for indoor PM of outdoor origin.