Indoor air quality and its determinants in tropical child care centers

This cross-sectional study aims to investigate indoor pollutants concentrations in child care centers (CCCs) and evaluate their determinants involving representative samples in Singapore. Measurements were performed for air temperature, relative humidity, air velocity, ventilation rates, carbon dioxide, carbon monoxide, ozone, fine particle mass, bacteria and fungi while information on CCC characteristics and maintenance activities were collected via a combination of inspection and interviews. It was found that due to higher ventilation rates, indoor CO2 concentration levels were lower in Singapore CCCs compared to those in the cold climates. Determinants of indoor pollutant levels from outdoor and indoor sources and maintenance activities were evaluated with regression analyses based on mass balance principles. Indoor carbon dioxide was positively associated with outdoor concentrations and occupant density while only outdoor levels significantly determined indoor carbon monoxide concentrations. For PM2.5, outdoor concentration, carpeted floor, presence of curtains and soft toys, recent renovation, shelf area and fan cleaning frequencies were positively associated with indoor levels while determinants of indoor ozone include outdoor concentration, shelf area and table cleaning. Increased human related bacteria levels were associated with high occupant densities and irregular floor but regular table cleaning frequencies. Outdoor concentration, curtain types and floor cleaning were significant determinants for environmental bacteria. Outdoor concentrations, presence of dampness, irregular floor and fan cleaning were associated with increased indoor mesophilic fungi levels. For indoor xerophilic fungi, levels were associated with outdoor concentrations, curtain types, dampness, occupant density and floor cleaning. We conclude that our findings confirm the important influence of indoor sources and maintenance activities on indoor concentrations of pollutants in Singapore CCCs. Future epidemiological analyses in CCCs should consider these determinants in classifying exposures as surrogate indicators of sources and cleaning activities.