A search for a threshold in the relationship of air pollution to mortality: a reanalysis of data on London winters.

The relationship between air pollution and increased risk of mortality has been explored previously using data on 14 winters in London. The results of these analyses have been used to determine a no-observable-effects level. This reanalysis of the data finds no evidence to support the existence of a no-effects level. Further, the reanalysis suggests that the estimated pollution-mortality relationship exists even in nonepisodic winters, when British Smoke readings were less than 500 micrograms/m3.