Abstract
PM10 mass, particle number (N) and CO2 concentrations, particle number size distributions and meteorological parameters were determined with high time resolution, and daily aerosol samples were collected in the PM10–2.0 and PM2.0 size fractions for chemical analysis in the middle of a university lecture hall for one week. Median concentrations for the PM10 mass and N of 15.3 μg m−3 and 3.7 × 103 cm−3, respectively were derived. The data are substantially smaller than the related outdoor levels or typical values for residences. There were considerable concentration differences for workdays, weekends and various lectures. Main sources of PM10 mass include the usage of chalk sticks for writing, wiping the blackboard, ordinary movements and actions of students and cleaning. High PM10 mass concentration levels up to 100 μg m−3 were realised for short time intervals after wiping the blackboard. The mass concentrations decreased rapidly after the emission source ceased to be active. Two classes of coarse particles were identified. General indoor dust particles exhibited a residence time of approximately 35 min, while the residence time for the chalk dust particles was approximately 20 min as lower estimates. Emission source rate for wiping the blackboard was estimated to be between 8 and 14 mg min−1. This represents a substantial emission rate but the source is active only up to 1 min. Suspension of the chalk (made mainly of gypsum) dust particles was confirmed by enrichment of Ca and S in the hall with respect to ambient urban aerosol. Contribution of ambient aerosol via the heating, ventilation and air conditioning (HVAC) facility was considerable for time intervals when the indoor sources of PM10 mass were not intensive. The HVAC facility introduces, however, the major amount of aerosol particles from the outdoors as far as their number concentration is regarded. Mean contribution of ultrafine particles to the total particle number was (69 ± 7)%, which is smaller than for the related outdoor urban environment. This can indicate aged ultrafine aerosol. The major amounts of CO2 arrive from the corridors through open doors by infiltration. Spatial distribution of the PM10 mass concentration within the hall was derived by CFD modelling, and spatial inhomogeneities were obtained.
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