Characterization of particle number concentrations and PM2.5 in a school: influence of outdoor air pollution on indoor air
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Background, Aim and Scope
The impact of air pollution on school children’s health is currently one of the key foci of international and national agencies. Of particular concern are ultrafine particles which are emitted in large quantities, contain large concentrations of toxins and are deposited deeply in the respiratory tract.
Materials and methods
In this study, an intensive sampling campaign of indoor and outdoor airborne particulate matter was carried out in a primary school in February 2006 to investigate indoor and outdoor particle number (PN) and mass concentrations (PM2.5), and particle size distribution, and to evaluate the influence of outdoor air pollution on the indoor air.
For outdoor PN and PM2.5, early morning and late afternoon peaks were observed on weekdays, which are consistent with traffic rush hours, indicating the predominant effect of vehicular emissions. However, the temporal variations of outdoor PM2.5 and PN concentrations occasionally showed extremely high peaks, mainly due to human activities such as cigarette smoking and the operation of mower near the sampling site. The indoor PM2.5 level was mainly affected by the outdoor PM2.5 (r = 0.68, p < 0.01), whereas the indoor PN concentration had some association with outdoor PN values (r = 0.66, p < 0.01) even though the indoor PN concentration was occasionally influenced by indoor sources, such as cooking, cleaning and floor polishing activities. Correlation analysis indicated that the outdoor PM2.5 was inversely correlated with the indoor to outdoor PM2.5 ratio (I/O ratio; r = −0.49, p < 0.01), while the indoor PN had a weak correlation with the I/O ratio for PN (r = 0.34, p < 0.01).
Discussion and conclusions
The results showed that occupancy did not cause any major changes to the modal structure of particle number and size distribution, even though the I/O ratio was different for different size classes. The I/O curves had a maximum value for particles with diameters of 100–400 nm under both occupied and unoccupied scenarios, whereas no significant difference in I/O ratio for PM2.5 was observed between occupied and unoccupied conditions. Inspection of the size-resolved I/O ratios in the preschool centre and the classroom suggested that the I/O ratio in the preschool centre was the highest for accumulation mode particles at 600 nm after school hours, whereas the average I/O ratios of both nucleation mode and accumulation mode particles in the classroom were much lower than those of Aitken mode particles.
Recommendations and perspectives
The findings obtained in this study are useful for epidemiological studies to estimate the total personal exposure of children, and to develop appropriate control strategies for minimising the adverse health effects on school children.
KeywordsI/O ratios Particle number concentration PM2.5 Aitken mode particles School
We would like to thank Mr. Mick Dobbyn, the principal of the school, for his support during the whole sampling campaign period. We are grateful to the representatives of the Parents and Citizens Association of the school, for their valuable suggestions on the project. The technical assistance received from Dr. Rohan Jayaratne and Dr. Graham Johnson was greatly appreciated. This project was funded by Queensland Transport and the data analysis was supported by Research Grants 87PK and PB0G from the Hong Kong Polytechnic University.
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