4.1. Air temperature and RH
Along with the decrease of outdoor temperature indoor temperature also decreased with mean values of around
11 oC. For the classrooms of elementary and secondary school air temperature and RH shall be in the range of 16-18
oC and 30%-80% [17] respectively. Therefore, the existing heating systems in the classrooms were not sufficient to
create recommended thermal environments for the children in winter.
4.2. CO2 concentrations
According to the indoor air quality standard [15], daily mean value of indoor CO2 concentration must be less
than 1000 ppm in occupied indoor environments. Health standard for classroom ventilation in elementary and
secondary school [18] specifies that CO2 concentration in classrooms must be less than 1500 ppm at any time. In our
study, in winter, CO2 concentration in the classrooms was measured more than 1000 ppm in over 60% of schooltime
and more than 1500 ppm in 40% of schooltime. Obviously, when all of the doors and windows were closed in
winter, it was insufficient to get required air exchanges in winter if merely relying on natural ventilation.
4.3. Other air pollutants
According to the results shown above, HCHO, acetaldehyde and TVOCs were kept in safe and acceptable levels
in the classrooms; but indoor PM pollution was at a severe situation, especially in winter, due to the high ambient
PM pollution. As shown in previous publication (GB3095-2012), the children are suffering from “heavily polluted”
or “severely polluted” environments either indoors or outdoors.
In our study, the indoor/outdoor (I/O) ratio of PM2.5 varied in the rage of 0.84–1.23 in autumn and 0.86-0.95 in
winter. The high I/O ratio suggested that most of the fine particles in the naturally ventilated indoor spaces were
from outdoor air. Furthermore, PM1.0 indicated to be the primary component of PM10 as the ratio of PM1.0 to PM10
was up to 0.71-0.86 in autumn and 0.78-0.86 in winter.