Relationships between Indoor and Outdoor Ultrafine Particles in 96 Homes in Windsor, Ontario

Jill Kearney (1), LANCE WALLACE (2), Xiaohong Xu(3), Keith Van Ryswyk (1), Hongyu You(1), Ryan Kulka(1), Amanda Wheeler(1)

(1) Health Canada, Ottawa, Canada (2) Reston, VA (3) University of Windsor

     Abstract Number: 385
     Last modified: November 9, 2009

Abstract
Ultrafine particles continue to be of interest with respect to the health effects of particulate matter. Few data on indoor and outdoor levels of ultrafine particles exist in Canada. As part of the Border Air Quality Strategy, Health Canada has conducted a series of exposure assessment studies investigating the relationship between personal, indoor and outdoor air pollutants in Windsor, Ontario. During 2005 and 2006, 48 non-smoking adults and 48 asthmatic children (aged 9-12 years), respectively, participated in an exposure study examining indoor and outdoor levels of ultrafine particles. At each participant’s home, indoor and outdoor 30-second average levels were measured for 10 minutes each hour using a P-Trak (TSI Inc.). Sampling was carried out for 5 consecutive days in summer 2005 and winter and summer 2006. Other measures included air change rate, temperature, and relative humidity. Information on daily activities, housing characteristics and proximity to traffic sources was also collected.
This is one of the first studies to measure indoor and outdoor ultrafine levels at multiple homes in different seasons. Approximately 500,000 30-second average indoor and outdoor ultrafine measurements were collected and analysed. Median indoor particle counts were 2700 cm^(-3) (summer 2005), 2600 cm^(-3) (summer 2006) and 3700 cm^(-3) (winter 2006). Median outdoor particle counts were 10700 cm^(-3) (summer 2005), 6400 cm^(-3) (summer 2006) and 11800 cm^(-3) (winter 2006). Maximum levels were near the maximum reading of the P-Traks (500,000 cm^(-3)). Outdoor levels exceeded indoor levels 75-86% of the time (lower in summer 2006 when outdoor levels were lower). Outdoor UFPs measured simultaneously at various homes across the city showed similar time trends, indicating relatively low spatial variability compared to temporal variability. More variability was seen in winter weeks, indicating the presence of more local outdoor sources. Outdoor levels peaked during morning and afternoon rush-hours. In summer 2005 there was also a noticeable mid-day peak, perhaps as a result of nucleation activity that was not as evident in summer 2006.
Indoor levels were lowest in the night-time hours, with higher levels around noon and maximum levels around the dinner hour (5-7 PM). The deposition rate of indoor UFPs was determined directly from observed decay rates from large (>20,000 cm^(-3)) peaks lasting at least four hours, and correcting these rates using observed air exchange rates. Initial estimates of the decay rates suggest an increased average rate compared to fine particles with a range of rates across homes from about 0.4 to 1.2 h^(-1).
Relationships of outdoor UFPs with other outdoor pollutants, meteorological and traffic data will be examined. Relationships of indoor UFPs and time activity data will also be examined. Long term exposure estimates for indoor and outdoor UFP levels will be derived from the short-term data using a validated model.