[Particulate matter in classrooms--problem and the impact of cleaning and ventilation with the City of Frankfurt am Main as an example].

BACKGROUND

Indoor air quality in schools, especially the levels of particulate matter in classrooms, have become a matter of great public concern in Germany, Convenient recommendations to improve the hygienic situation in classrooms via cleaning and ventilation are often not followed. Here, data on particulate matter in the indoor air of classrooms, before and after intensified cleaning, are reported.

MATERIAL AND

METHODS

In the winter of 2006, analyses for particulate matter were done in two primary schools in Frankfurt/M, one of them located in a rural area the other one in an inner city area of Frankfurt/M. Particulate matter (PM10) was analysed by laser beam technology, the data documented every five minutes from 8 am to 2 pm. In parallel, a documentation of the number of persons present in the room, their activity and ventilation was done according to a standardised protocol. Measurements were collected for a period of three weeks. During the first week, the normal school situation was analysed, i.e., the classrooms were ventilated as usual and were cleaned by wet wiping twice a week. During the second and third weeks, the rooms were cleaned every day, so that the effect of intensified cleaning could be studied. In winter 2007, these measurements were continued for one week in two classrooms of a passive house school, following the identical study protocol.

RESULTS

During the first week--wet cleaning twice a week--mean particulate concentrations of 86 microg/m3 (median 60 microg/m3) were obtained, during the 2nd and 3rd weeks--wet cleaning every school day mean concentrations of 60 microg/m3 (median 53 microg/m3)--with great differences on different days. Especially during and after handicraft (casting candles) lessons, maximum levels up to >1000 microg/m3 were analysed. Although an impact of cleaning on levels of indoor particles could be established, indoor PM10 levels were dominated by indoor factors, such as occupancy and activity of the persons in the room. After substraction of the outdoor PM10 levels from the indoor levels, the "indoor part" was ca. 50 microg/m3 before, and ca. 30 microg/m3 during intensified cleaning. Further detailed investigations showed the predominance of particles >1 microm indoors, which could easily be diminished by cleaning and ventilation. Indoor particles <0.5 microm, however, were increased via ventilation.

CONCLUSION

In classrooms, generally higher indoor levels of air particulate matter are detected than outdoors. Particulate matter in the indoor air of classrooms is to be considered as an indicator of low hygiene and of increased and avoidable heath risk for pupils and teachers. Our data indicate the relevance of cleaning--and with regard to PM <1 microm also of ventilation--for the reduction of particulate matter in classrooms. Therefore, these measures should be taken to improve indoor air quality in schools.