Urban Measurements of Outdoor-Indoor PM2.5 Concentrations and Personal Exposure in the Deep South. Part I. Pilot Study of Mass Concentrations for Nonsmoking Subjects
The interpretation of epidemiological results relating PM2.5 and personal exposure depends on linking exposure to mass concentration in ambient outdoor air. To obtain exploratory information on this relationship, outdoor, indoor, and personal exposure measurements have been made for a small sample population in Birmingham, AL. The observations covered 2 seasons, summer and winter, for a sample of 10 healthy, nonsmoking working class people of ages from 25 to 63 years. The participants experienced activity patterns that were similar and were believed to be typical of the climate, building conditions, and transportation habits in the Deep South. On average, these involved indoor activities more than 96-98% of the time, with occupancy in their residences 56-59% of the time. The methods adapted for the study included the use of individual activity diaries and involved sampling for 48 h average mass concentrations using conventional filtration and gravimetric mass determination. The homes of the participants were used to represent indoor conditions. These residences were characterized by a visual description and estimation of the air exchange rate and infiltration coefficient using a pressurized blower method. The results showed a weakly correlated but consistent linear relationship between personal exposure and indoor or outdoor ambient air PM2.5 mass concentration. The mean personal exposure in mu g /m3 in 48 h was found to be 18.6 +/- 6.4 mu g /m3 and 10.0 +/- 3.3 mu g /m3 in summer and winter, respectively. These values lie between the outdoor and indoor concentrations in summer, but were slightly less than the other two in winter. The measurements of outdoor concentrations taken at each residence correlated with a spatial average of community monitoring stations within the city, but differed locally in magnitude. A weak, linearly proportional relationship was found between indoor PM2.5 concentrations and the product of the outdoor concentration and the residential infiltration factor. Application of a simple mass balance model yielded results similar to a much larger study in California. There was some evidence of a ''personal cloud'' present in 9 of 30 observations in summer, but only 4 of 30 observations in winter.
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