Effect of indoor and outdoor sources on indoor particle concentrations in South Korean residential buildings

Highlights: • On-site measurements of particle number concentrations. • Occupancy survey in 10 residential buildings. • Results presented on indoor peak event, loss rate coefficient, and particle exposure. • Exposure in South Korean residential apartments is predominantly attributed to outdoor sources. The rising indoor air pollution from particles is a cause for concern especially in houses where children and the elderly reside. In South Korea, assessment of exposure to particle number (PN) in residential apartments, which account for 76% of all houses, is limited. In our study, the indoor and outdoor PN (sizes 0.3–10.0 µm) concentrations were measured in ten typical apartments for 24 h each. In addition, the occupants' schedules were examined by conducting a survey. Results showed that the average outdoor PN concentrations were 0.30–4.37 × 10⁹/m³ with very large deviations. Indoor peak events were mainly caused by cooking, and total emitted particles were 0.01–81.3 × 10¹³ particles. Indoor PN concentrations were sustained for a long time because of inefficient ventilation that led to lowered attenuation. Indoor particles are generated during various indoor activities. The daily-integrated particle exposures were 21.4% and 78.6% for indoor and outdoor sources, respectively. Thus, outdoor sources were the predominant sources of particle exposure compared with indoor sources. In conclusion, penetration from outdoor sources needs to be reduced by adding air filtration to improve the airtightness of buildings when introducing outdoor air to lower the indoor PN concentration.