Influence of different indoor activities on the indoor particulate levels in residential buildings

This study reports 24-hour measurements of indoor particulate levels in 8 residential premises in Hong Kong. The 24-hour respirable suspended particulate (RSP) levels varied from 44.9 to 119.4 μg·m^-3 and the corresponding total suspended particulate (TSP) levels varied from 45.8 to 122.2 μg·m^-3. These levels are higher than those measured in other countries. This was found to be related to the poor quality of outdoor air found in Hong Kong and also to the different indoor activities practised by these families. During the measurements indoor activities were recorded and ventilation rates at some of the sites were also measured using the carbon dioxide decay technique. A significant rise of particulate level was detected during cooking, smoking and burning of incense. In the study, particulate levels over 5,000 μg·m^-3 were observed during some cooking activities. Particulate levels when people were smoking were 2-3 times higher than the relative background level. Incense burning in some families produced a peak concentration of particulates around 2,000 μg·m^-3 if the ventilation was poor. The effect of rain was to wash the outdoor particulates from the air and at the same time the indoor particulate level fell if the ventilation rate was high enough. It was observed that about 20% of the indoor dust level could be reduced in less than 1 h when there was heavy rain. It was also found in the study that a very high indoor RSP to TSP ratio of 82-98% existed indoors.