Indoor air quality investigations at five classrooms

Five classrooms, air-conditioned or naturally ventilated, at five different schools were chosen for comparison of indoor and outdoor air quality. Temperature, relative humidity (RH), carbon dioxide (CO2), sulphur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), 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 PM10concentrations exceeded the Hong Kong standards, and the maximum indoor PM10level was even at 472 μg/m3. Air cleaners could be used in classrooms to reduce the high PM10concentration. Indoor CO2concentrations often exceeded 1,000 μl/1 indicating inadequate ventilation. Lowering the occupancy and increasing breaks between classes could alleviate the high CO2concentrations. Though the maximum indoor CO2level reached 5,900 μl/1 during class at one of the sites, CO2concentrations were still at levels that pose no health threats.