Elsevier

Atmospheric Environment

Volume 41, Issue 4, February 2007, Pages 854-866
Atmospheric Environment

Particulate matter in the indoor air of classrooms—exploratory results from Munich and surrounding area

https://doi.org/10.1016/j.atmosenv.2006.08.053Get rights and content

Abstract

Numerous epidemiological studies have demonstrated the association between particle mass (PM) concentration in outside air and the occurrence of health related problems and/or diseases. However, much less is known about indoor PM concentrations and associated health risks. In particular, data are needed on air quality in schools, since children are assumed to be more vulnerable to health hazards and spend a large part of their time in classrooms.

On this background, we evaluated indoor air quality in 64 schools in the city of Munich and a neighbouring district outside the city boundary. In winter 2004–2005 in 92 classrooms, and in summer 2005 in 75 classrooms, data on indoor air climate parameters (temperature, relative humidity), carbon dioxide (CO2) and various dust particle fractions (PM10, PM2.5) were collected; for the latter both gravimetrical and continuous measurements by laser aerosol spectrometer (LAS) were implemented. In the summer period, the particle number concentration (PNC), was determined using a scanning mobility particle sizer (SMPS). Additionally, data on room and building characteristics were collected by use of a standardized form. Only data collected during teaching hours were considered in analysis. For continuously measured parameters the daily median was used to describe the exposure level in a classroom.

The median indoor CO2 concentration in a classroom was 1603 ppm in winter and 405 ppm in summer. With LAS in winter, median PM concentrations of 19.8 μg m−3 (PM2.5) and 91.5 μg m−3 (PM10) were observed, in summer PM concentrations were significantly reduced (median PM2.5=12.7 μg m−3, median PM10=64.9 μg m−3). PM2.5 concentrations determined by the gravimetric method were in general higher (median in winter: 36.7 μg m−3, median in summer: 20.2 μg m−3) but correlated strongly with the LAS-measured results. In explorative analysis, we identified a significant increase of LAS-measured PM2.5 by 1.7 μg m−3 per increase in humidity by 10%, by 0.5 μg m−3 per increase in CO2 indoor concentration by 100 ppm, and a decrease by 2.8 μg m−3 in 5–7th grade classes and by 7.3 μg m−3 in class 8–11 compared to 1–4th class. During the winter period, the associations were stronger regarding class level, reverse regarding humidity (a decrease by 6.4 μg m−3 per increase in 10% humidity) and absent regarding CO2 indoor concentration. The median PNC measured in 36 classrooms ranged between 2622 and 12,145 particles cm−3 (median: 5660 particles cm−3).

The results clearly show that exposure to particulate matter in school is high. The increased PM concentrations in winter and their correlation with high CO2 concentrations indicate that inadequate ventilation plays a major role in the establishment of poor indoor air quality. Additionally, the increased PM concentration in low level classes and in rooms with high number of pupils suggest that the physical activity of pupils, which is assumed to be more pronounced in younger children, contributes to a constant process of resuspension of sedimented particles. Further investigations are necessary to increase knowledge on predictors of PM concentration, to assess the toxic potential of indoor particles and to develop and test strategies how to ensure improved indoor air quality in schools.

Introduction

Numerous epidemiological studies have been carried out during the last decades which demonstrated the correlation between the pollution of outside air with toxic substances and the occurrence of health related problems and/or diseases. On the background of these findings, particularly in recent years the focus of research has clearly shifted towards particulate matter, notably fine particles—e.g. PM2.5—and ultra fine particles with diameters less than 100 nm (EPA (US-Environmental Protection Agency), 2004; WHO (World Health Organization), 2004).

Stationary outdoor particle mass (PM) concentration is a frequently used indicator of PM exposure in large epidemiologic cohort studies and has been shown to be associated with health risks on the population level. Stationary outdoor PM concentration, however, is only of limited use for the assessment of individual exposure level and thus estimates of relative risk derived from these studies might be biased by measurement errors. Individual exposure to PM occurs in diverse microenvironments, where particles may originate from a wide variety of sources. In the indoor environment, in which people spend most of their time, both indoor and outdoor sources contribute to PM levels. Indoor PM is affected by ambient concentrations, air exchange rates, penetration factors, as well as deposition and resuspension mechanisms. In this complex microenvironment, activities such as cooking, cleaning, walking, and particularly smoking cause the formation of PM in indoor air.

Although numerous measurements of PM in the outside air have been conducted, only few data on indoor air pollution are available. Investigations into PM are even more rare for schools and related indoor facilities than for other microenvironments. As school-aged children spend approximately 30% of their daytime in school and may be regarded as particularly vulnerable to potential health hazards, more precise data on exposure to air pollution in this setting is urgently required.

Therefore, the aim of the present study was to determine the quality of indoor air in different seasons in a large number of schools in Bavaria, in particular the concentration of particulate matter. Furthermore, we aimed for the comparison of results on PM concentrations obtained by two different established techniques and for the identification of potential determinants of PM concentration in exporative analysis.

Section snippets

Study description and sampling sites

Sixty-four primary and secondary schools located in the northern part of the city of Munich and in a neighbouring rural district took part in the study, thus allowing data collection from city, rural and small town areas. In the winter measurement period (December 2004 to March 2005) 92 classrooms, and in the summer measurement period (May to July 2005) 75 classrooms, respectively, were included. Fifty-eight classrooms were measured at both occasions.

In each classroom measurements were done

Results

The condition of the school buildings and the furnishings and fittings of the classrooms were extremely variable. The size of the classrooms ranged between 47–98 m2 (median: 68 m2) and the volume between 160–437 m3 (median: 222 m3). During the period of occupancy (ca. five school hours daily) the classrooms were occupied by 9–35 subjects (median: 24). The attendance (number of pupils) in winter did virtually not differ from attendance in summer. As usual for school buildings in Germany, none of

Discussion

In this study, for the first time, results on various particle related parameters in indoor air are presented for a large number of schools. Our results clearly show that exposure to particulate matter in school is high. The wide range of PM concentrations indicate the large potential for reduction and the need for identification of factors responsible for this variability. We observed a strong seasonal variability, with air quality being particularly poor in winter. Further parameters

Conclusion

Our results as well as findings from earlier studies clearly show that exposure to particulate matter in school is high. In our explorative analysis we were able to identify parameters correlated with increased concentrations of PM such as high CO2 concentrations and low class level. Only in winter additionally small room size and high number of occupants were associated with increased PM. Further research is needed to confirm these findings and identify additional determinants of PM

Acknowledgement

This study was funded by the Bavarian State Ministry of the Environment, Public Health and Consumer Protection. The authors would like to thank Mr. Flower for his help in preparing the manuscript.

References (27)

  • S.T. Ebelt et al.

    Exposure to ambient and nonambient components of particulate matter. A comparison of health effects

    Epidemiology

    (2005)
  • EPA (US-Environmental Protection Agency) (Eds.), 2004. Air quality criteria for particulate matter....
  • H. Fromme et al.

    Elemental carbon and respirable particulate matter in the indoor air of apartments and nursery schools and outdoor air in Berlin (Germany)

    Indoor Air

    (2005)
  • Cited by (0)

    View full text