Canadian Journal of Statistics

Acute health effects of transported air pollution: A study of children attending a residential summer camp

Journal Article

Abstract

Sulphur dioxide was very low throughout the study period, with the highest hourly value reaching only 8.9 ppb. Sulphuric acid concentrations were usually below the detectable limit of 2 μg/m3. The highest hourly concentrations of 5 μg/m3 were attained on days of relatively low sulphur concentrations. Due to the low concentrations of SO2 and H2SO4, these environmental variables will not be considered further here.

The environmental factors of interest are PM2.5, SO4=, O3 (one‐hour maximum), temperature, and relative humidity, where SO4=, temperature, and relative humidity are averages of continuous measurements over the sampling period. The values of these variables are listed by lung‐function testing period in Table 1. Two periods of elevated pollution levels occurred during the study period, the first lasting from 30 June P. M. to 1 July P. M., and the second from 3 July P. M. to 4 July P. M. On four of the nine days, the current Ontario air‐quality standard for ozone of 80 ppb (1‐hour maximum) was attained or exceeded. A back‐trajectory analysis conducted by Environment Canada showed air‐mass transport from the Ohio valley on both 30 June and 3 July.

Fifty‐two campers, including 23 asthmatics (12 boys and 11 girls) and 29 nonasthmatics (16 boys and 13 girls), completed all components of the study. The mean values of the three lung‐function indictors (FVC, FEV1.0, and PEF) for asthmatics and nonasthmatics are given in Table 2 for each of 18 testing periods. The first testing period (29 June P. M.) was considered as a training session and is not included in this presentation. The three lung‐function responses tend to follow a similar pattern over time, with the highest responses occurring at the beginning of the camp, followed by a steep decline for several subsequent testing periods. A gradual increase is then observed, with some stabilization occurring near the completion of the camp. The child‐specific variation in lung function over time is given in Table 3. There are appreciable differences in the variance of the lung‐function measurements between children, with asthmatics tending to exhibit larger variances than their nonasthmatic counterparts.

Table 4 gives the frequency of a positive response to several questions concerning respiratory symptoms for each session for asthmatics and nonasthmatics respectively. Here, a positive response to Cough and Sneeze is defined as an occurrence of these symptoms five or more times since the previous lung‐function testing session. The number of children using medication since the last session is also reported.

The consultants were asked to explore the possibility that the environmental factors in Table 1 may affect lung‐function performance as measured by the parameters in Table 2 or occurrence of the respiratory symptoms summarized in Table 4. Differences in response between asthmatics and nonasthmatics are also of interest.

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