Indoor air quality investigations at five classrooms.

Five classrooms, air-conditioned or naturally ventilated, at five different schools were chosen for comparison of indoorand outdoor air quality. Temperature, relative humidity (RH), carbon dioxide (C02), sulphur dioxide (S02), nitric oxide (NO), nitrogen dioxide (N02), particulate matter with diameter less than 10 μm (PM10), formaldehyde (HCHO), and total bacteria counts were monitored at indoor and outdoor locations simultaneously. Respirable particulate matter was found to be the worst among parameters measured in this study. The indoor and outdoor average PM10 concentrations exceeded the Hong Kong standards, and the maximum indoor PM10 level was even at 472 μg/m3. Air cleaners could be used in classrooms to reduce the high PM10 concentration. Indoor C02 concentrations often exceeded 1,000 μl/l indicating inadequate ventilation. Lowering the occupancy and increasing breaks between classes could alleviate the high C02 concentrations. Though the maximum indoor C02 level reached 5,900 μl/l during class at one of the sites, C02 concentrations were still at levels that pose no health threats.