Factors affecting variability in infiltration of ambient particle and gaseous pollutants into home at urban environment

The majority of urban residents live in places with air quality exceeding World Health Organization guidelines. To quantify infiltration of outdoor pollution, and key factors affecting it, common outdoor air pollutants (PM2.5, NO2, and O-3) were measured at 49 homes in Hong Kong. Infiltration factors (F-inf) were derived based on linear regression of simultaneous indoor and outdoor measurements for each pollutant at each home. F-inf estimated based on data for home occupancy, during which people were actually exposed, differed by up to 22%, 73% and 63% for PM2.5, NO(2)( )and O-3, respectively, from estimates based on whole monitoring data. This indicates the importance of separating occupancy time to quantify F-inf for exposure estimation. The inter-home variability in occupancy F-inf ranged from 0.11 to 1.00 (mean: 0.75) for PM2.5, 0.14 to 1.00 (mean: 0.53) for NO2, and 0.05 to 0.95 (mean: 0.47) for O-3. Ventilation practices (e.g., window opening duration and air-conditioning on/off) explained 48%, 20%, and 10% of the inter-home variations in PM2.5, NO2 and O-3 F-inf, respectively. Use of air purifiers explained an additional 8%-9% of variations for PM2.5 and NO2. Thus, there is potential to reduce outdoor infiltration by modifying occupant behaviours. Compared to PM2.5 (R-2 = 0.63), the developed models explained less variability in F-inf for NO2 (R-2 = 0.40) and O-3 (R-2 = 0.10). These two gases are chemically reactive. Further investigation, supported by additional measurements of related chemical species, is needed to improve understanding of infiltration process of reactive gases such as NO2 and O-3.