Chemical and morphological properties of particulate matter (PM10, PM2.5) in school classrooms and outdoor air
Introduction
Ambient particulate matter (PM) is considered to be an important indicator of outdoor air quality, since a number of health problems have been associated with high concentrations (WHO, 2004, US-EPA, 2004). Short-term epidemiological studies have revealed respiratory and cardiopulmonary effects, increased health care utilization and increased cardiopulmonary mortality (Peters et al., 2000, Samet et al., 2000, Le Tertre et al., 2002). Increased mortality due to pulmonary and cardiovascular diseases has been indicated in long-term studies (Krewski et al., 2000, McDonnell et al., 2000, Lipfert et al., 2000, Hoek et al., 2002, Gehring et al., 2006, Miller et al., 2007). In a large cohort study of 552,000 subjects with a follow-up period of 16 years (American Cancer Society Study), each additional 10 μg PM2.5 m−3 led to an increase of cardiovascular mortality by 8–18% (Pope et al., 2004).
Although the school environment normally lacks typical indoor PM sources such as smoking and cooking, many children are present in a limited space over a period of several hours. There is growing evidence of comparatively high concentrations of PM in classrooms (e.g., Janssen et al., 2001, Lahrz et al., 2003, Link et al., 2004, Son et al., 2005, Fromme et al., 2007, Stranger et al., 2007). These findings may be explained by: (1) insufficient ventilation in schools (especially in winter), (2) infrequently and unthoroughly cleaned indoor surfaces, and (3) a large number of pupils in relation to room area and volume, with constant resuspension of particles from room surfaces.
However, these high concentrations do not necessarily result in higher health risks to pupils, because the sources and the composition of PM in indoor air may differ from those in outdoor air (Schwarze et al., 2006). Therefore, the composition of indoor PM and its sources need to be clarified.
To the best of our knowledge, so far there are only limited data available concerning the chemical properties of PM in schools, i.e., data on water-soluble ion concentrations derived from Greek and American schools (Diapouli et al., 2008, John et al., 2007) and on elemental carbon (EC) from German, Dutch and American classrooms (Janssen et al., 2001, Lahrz et al., 2003, Fromme et al., 2005, Ward et al., 2007).
The aim of the present study was to characterize the chemical and morphological properties of PM (PM10 und PM2.5) in classrooms and in corresponding outdoor air. For this purpose the following components of PM were quantified: water-soluble ions, elemental carbon (EC), organic carbon (OC) and the absorption coefficient of the filters. This information should improve understanding of the sources of the high PM in schools and how these sources contribute to overall exposure.
Section snippets
Study objects and sampling time
PM was collected in the indoor air of two classrooms of one primary school and simultaneously in outdoor air in front of the windows on a balcony. At a school located in northern Munich, sampling was carried out in October and November 2005 for a time period of 6 weeks. The school is located in a densely populated residential area on a side road about 160 m away from a very busy street. No specific industrial sources for emissions are known of in this area. The school was erected in 1970. Both
Results
The mean daily indoor temperature during school time did not vary considerably (21–24 °C), while a large variability existed in outdoor temperature (−6 °C to 19 °C). Indoor relative humidity varied between 33% and 55%, and outdoor humidity between 47% and 99%.
Discussion
Our investigation is one of the first attempts to determine and compare the composition of indoor and outdoor particulate matters in schools. The data indicate that indoor PM concentrations are substantially higher than outdoors. These increased concentrations are accompanied by a reduced proportion of EC, OC and most of the ions, leaving the greater percentage of indoor PM unexplained. It seems that particularly larger particles originate from indoor sources. Analysis with the SEM/EDX suggests
Conclusion
Our findings on morphological characteristics and chemical constituents of particulate matter in classrooms suggest that important indoor sources of especially coarse PM exist in this microenvironment. Despite the inherent limitations of our somewhat rough model estimates, we can conclude that 24% of PM10 and 43% of PM2.5 were of ambient origin. Resuspension of these comparatively large particles thus appears to play a major role of PM exposure in classrooms.
The comparatively high proportion of
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2023, Environmental AdvancesCitation Excerpt :Among off-peak hour periods, MOP showed the highest average ratio of BCff (3.22) than AOP, MP and EP. Their concentration ratio levels remained similar during MP, MOP and EP, suggesting that PM2.5 measured in classrooms has major sources other than outdoor particles, as previously observed by Fromme et al. (2008). Black carbon is a component of the PM2.5 emitted from diesel exhausts.