Characterizing Ultrafine Particle Exposures in Two Types of Indoor Environments: San Francisco Bay Area Classrooms and Beijing High-Rise Apartments.

摘要

In this dissertation, ultrafine particle (UFP) exposure concentrations are characterized and the factors influencing those concentrations are explored, within two microenvironments that had hitherto not been investigated: San Francisco Bay Area elementary school classrooms and Beijing high-rise apartments.;Children between the ages of 6 and 11 years old living in California spend an average of 10% of their time in school, second only to the amount of time spent at home (53%). In addition, children are considered to be more susceptible to some health effects resulting from pollutant exposures than are adults. To contribute towards a characterization of children's exposure to ultrafine particles, a field study was conducted in six classrooms in the San Francisco Bay Area. The data collection phase of this study involved monitoring particle number (PN) concentrations and the concentrations of three gaseous co-pollutants (CO2, NO, O3) for two to four school days in each classroom.;The average indoor PN concentration during periods of student occupancy in the six classrooms ranged from 5.2 x 103 to 16.5 x 10 3 cm-3. Indoor sources had a relatively small influence on classroom PN concentrations, with only three significant source events detected during periods of student occupancy across the six classrooms. For this small sample of admittedly limited scope, the classrooms monitored in warmer months (i.e., June through early November) had both a higher outdoor and indoor average PN concentration during periods of student occupancy than those monitored during colder months (i.e., late November and early December). This higher exposure to outdoor generated particles during warm months was influenced by more frequent opening of doors and windows for the purpose of maintaining a comfortable temperature in the classroom. The mean daily-integrated UFP exposures of the students while in their classrooms was 50,000 cm -3 h d-1, which was approximately a factor of 6 less than the mean exposure calculated in a parallel study for a sample of children in San Francisco Bay Area homes.;The time-weighted average air-exchange rate for the six classrooms ranged from 1.1 to 10.8 h-1, and the accompanying range for the rate of ventilation per person was 4 to 27 L/s. Two of the classrooms utilized mechanical ventilation systems, while four were ventilated by means of doors and windows. In the case of the naturally ventilated classrooms, the ventilation rate generally exceeded the standard specified by the American Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE) when doors and/or windows were in an open state, but often fell below the standard otherwise. For the mechanically ventilated classrooms, the air-exchange rate appeared unnecessarily high in one case and too low in the other. Results from five of the six sites were analyzed to see if an increase in the air-exchange rate was accompanied by an increase in the indoor proportion of outdoor particles (IPOP); for four of the classrooms the data were so correlated. However, reducing the air-exchange rate as a strategy for decreasing the indoor level of outdoor generated particles is not recommended, and instead strategies were investigated for reducing the IPOP using active filtration.;Roughly 20% of the world's population lives in China, and yet research groups have only recently begun to investigate UFP concentrations in this region of the world. A field study was conducted in a sample of high-rise apartments in Beijing. The data collection phase of this study involved monitoring PN within four high-rise apartments for two to four days each. For two apartments, outdoor PN data were also collected. Temperature and state-change data loggers were used to record when occupant activities involving heat (e.g., cooking) were conducted and when door and window positions were changed, respectively. In all, ∼9 days of time-series data were collected.;Distinct indoor PN peaks independent of outdoor concentrations were observed on twenty-seven occasions during monitoring at the four apartments. Cooking was responsible for the majority of the observed indoor PN peaks. In one apartment, although the residents cooked infrequently themselves, a large number of indoor peaks appeared to result from the infiltration of emissions from cooking in neighboring apartments. The average indoor PN concentrations at the four apartments ranged from 2,800 to 29,100 cm-3. The apartment with the highest indoor concentration was influenced by the neighbors cooking, and the apartment with the lowest concentration only experienced two indoor PN peaks in two days and had two portable fan-filter air cleaners that operated almost continuously. For the apartments where outdoor PN data were also collected, 58% and 81% of the residents' total UFP exposure while at home was attributed to outdoor sources. (Abstract shortened by UMI.)