Mass concentrations of PM1.0, PM2.5 and PM10 directly measured by the instrument are given in Fig. 4. In
accordance with the significant outdoor pollution, indoor PM levels were also very high. Especially in December,
PM pollution in the classrooms was significantly exacerbated together with outdoor pollution. Most of the indoor
PM concentrations exceeded the corresponding outdoor concentrations in autumn, indicating that there were
considerable sources of PM pollution indoors, such as chalk powder. Moreover, as the outdoor PM concentration
reached a very high level in the experimental period in December, the strength of PM source inside the classrooms
indicated relatively smaller than the corresponding outdoor concentrations. This result implied that ambient PM
pollution in Wuhan was in a very serious situation in the winter, and could be a decisive factor for PM level in the
classrooms with an overwhelming impact.
Fig 5 shows the converted gravimetric values of PM2.5 concentration by using Equation 1. In autumn and winter,
the gravimetric concentrations of PM2.5 were far more than 75μg/m3, the limit of the daily mean value of PM2.5,
according to ambient air quality standards (GB3095-2012).