Indoor Air Quality Investigations at Five Classrooms

Abstract 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 mm (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 μ;g/m³. Air cleaners could be used in classrooms to reduce the high PM₁₀ concentration. Indoor CO₂ concentrations often exceeded 1,000 μl/l indicating inadequate ventilation. Lowering the occupancy and increasing breaks between classes could alleviate the high CO₂ concentrations. Though the maximum indoor CO₂ level reached 5,900 μl/l during class at one of the sites, CO₂ concentrations were still at levels that pose no health threats.