Size distribution of indoor particulate matter in 60 homes in Hong Kong

A detailed size distribution study of particulate matter was performed in 60 homes: 37 homes were studied in the winter and 23 in the summer. Levels of particulate matter were measured using several cascade impactors covering 8 size ranges. In the winter measurements, the mean 24-hour indoor PM_2.1 (particle mass 2.1 μm or smaller) and PM₁₀ concentrations were found to be 43.7 and 64.1 μg·m^-3, respectively, and the corresponding outdoor levels were 43.0 and 70.1 μg·m^-3. In the summer measurement, the mean 24-hour indoor PM_2.1 and PM₁₀ concentrations were found to be 27.2 and 43.7 μg·m^-3, respectively, and the corresponding outdoor levels were 23.6 and 39.6 μg·m^-3. It can be seen that the concentration of particulates in summer was appreciably lower than in the winter. The highest peak of concentration (over 20% by mass) was observed in the particulate size range of <0.4 μm both in the indoor and in the outdoor samples. The indoor/outdoor ratio of the particulate level in summer was higher than that in winter over all size ranges implying that indoor generation sources play an important role in keeping the indoor level high. Higher particulate levels were observed in homes with indoor activities such as smoking and incense burning, while lower particulate levels in both the indoor and the outdoor environments were measured during rain.