Residential indoor PM₁₀ and PM_2.5 in Hong Kong and the elemental composition

Indoor air particulate samples were collected in 34 homes and their adjacent outdoor environments in Hong Kong during the fall and winter seasons. It was found that the mean indoor PM_2.5 and PM₁₀ concentrations were 45.0 and 63.3 μg m^-3, respectively. The corresponding mean outdoor levels were 47.0 and 69.5 μg m^-3, respectively. The indoor particulate levels were found to be about 2-4 times higher than those in the homes in western countries where most are located in suburb areas with a much better ambient air quality. Pearson paired t-tests were conducted on the data and it was found that poor correlation was seen in the indoor and the outdoor particulate concentrations. This was probably due to the fact that windows were closed more often in the fall and winter seasons keeping the ventilation rate low, plus the factor that window type air conditioners were used commonly in Hong Kong, which again, constituted to a low air change rate. Both the indoor and the outdoor elemental compositions of the particulate samples collected in these 34 homes were identified by proton-induced X-ray emission analysis. Seventeen elements were identified. The mean inorganic elemental compositions in the indoor PM_2.5 and PM₁₀ samples were 6.4 and 10.2 μg m^-3, respectively while those in the outdoor samples were 7.9 and 14.1 μg m^-3, respectively. Enrichment factor analysis was performed and it was noted that those species existing in fine mode were highly enriched (bromine, lead, nickel, potassium, sulfur, vanadium and zinc) while those species existing in the coarse mode had their enrichment factors close to 1 (aluminum, calcium, iron, magnesium, silicon, sodium and titanium).