No abstract

Retired agronomist, New Zealand"It is incident to physicians, I am afraid, above all other men, to mistake subsequence for consequence. " 1 McGowan et al. 2 examined the coincidence of daily variations in the concentrations of fine particles (PM 10 ) in the air and the numbers of people admitted to New Zealand's Christchurch Hospital for treatment of cardiac or respiratory complaints from 1988 to 1998. They found that cardiac admissions were higher on high pollution days. Respiratory admissions were also higher on high pollution days. The admissions peaked two days after high pollution days, and this higher rate persisted with only slight diminution for the ensuing four days, and perhaps for longer. From the results, they concluded that particulate pollution caused significant morbidity and that measures to reduce particulate pollution could reduce hospital admissions for cardio-respiratory illness in the city.Mean concentration of PM 10 in Christchurch is 25 µg/m 3 (not 25 mg/m 3 as given in their Table 1). This is similar to the mean concentrations now being recorded in London or Birmingham, 3 and about half that recorded in Los Angeles. 4 People smoking 30 cigarettes a day inhale as much PM 10 as they would if they were continually breathing air containing 24,000 µg/m 3 of PM 10 . 5 There is no consensus as to how PM 10 causes these effects, if indeed it does, 6 or clinical evidence of the damage it causes at these low concentrations.Concentrations of SO 2 , NO, NO 2 , CO and PM 10 were monitored daily over the study period. The high concentrations of all pollutants recorded on some winter nights are a consequence of weather conditions, so variations in the concentrations of all these pollutants were highly correlated. For days for which there were no records of PM 10 concentrations, a missing value was calculated using the regression relationship between concentrations of PM 10 and CO.Because of the high correlations between concentrations of the several pollutants, there is difficulty in separating the effects of one from the others. 7 Although the data were available, the associations between other pollutants and hospital admissions were not examined, but they were discussed. Without question or qualification, all the observed effects were attributed to variations in concentrations of PM 10 .There were considerable differences between years in the number of admissions and in the concentrations of PM 10 . Concentrations of PM 10 were generally higher in the earlier years. There may have been twice as many admissions in the later years than in the earlier years. Aside from these secular trends, the number of admissions did not appear to be positively correlated with the mean yearly PM 10 concentrations. In this the results are similar to those of

Retired agronomist, New Zealand"It is incident to physicians, I am afraid, above all other men, to mistake subsequence for consequence. " 1 McGowan et al. 2 examined the coincidence of daily variations in the concentrations of fine particles (PM 10 ) in the air and the numbers of people admitted to New Zealand's Christchurch Hospital for treatment of cardiac or respiratory complaints from 1988 to 1998. They found that cardiac admissions were higher on high pollution days. Respiratory admissions were also higher on high pollution days. The admissions peaked two days after high pollution days, and this higher rate persisted with only slight diminution for the ensuing four days, and perhaps for longer. From the results, they concluded that particulate pollution caused significant morbidity and that measures to reduce particulate pollution could reduce hospital admissions for cardio-respiratory illness in the city.Mean concentration of PM 10 in Christchurch is 25 µg/m 3 (not 25 mg/m 3 as given in their Table 1). This is similar to the mean concentrations now being recorded in London or Birmingham, 3 and about half that recorded in Los Angeles. 4 People smoking 30 cigarettes a day inhale as much PM 10 as they would if they were continually breathing air containing 24,000 µg/m 3 of PM 10 . 5 There is no consensus as to how PM 10 causes these effects, if indeed it does, 6 or clinical evidence of the damage it causes at these low concentrations.Concentrations of SO 2 , NO, NO 2 , CO and PM 10 were monitored daily over the study period. The high concentrations of all pollutants recorded on some winter nights are a consequence of weather conditions, so variations in the concentrations of all these pollutants were highly correlated. For days for which there were no records of PM 10 concentrations, a missing value was calculated using the regression relationship between concentrations of PM 10 and CO.Because of the high correlations between concentrations of the several pollutants, there is difficulty in separating the effects of one from the others. 7 Although the data were available, the associations between other pollutants and hospital admissions were not examined, but they were discussed. Without question or qualification, all the observed effects were attributed to variations in concentrations of PM 10 .There were considerable differences between years in the number of admissions and in the concentrations of PM 10 . Concentrations of PM 10 were generally higher in the earlier years. There may have been twice as many admissions in the later years than in the earlier years. Aside from these secular trends, the number of admissions did not appear to be positively correlated with the mean yearly PM 10 concentrations. In this the results are similar to those of