Following people, rather than one pollution episode
Dockery and colleagues followed 8,111 adults in six US cities for 14–16 years. Their 1993 study compared mortality with city-level air pollution while accounting for individual factors such as smoking. It addressed sustained exposure, not the immediate effect of an hourly AQI reading.
What the comparison found
The adjusted mortality-rate ratio between the most and least polluted cities was 1.26, with a 95% confidence interval of 1.08–1.47. Associations were strongest for fine particles and sulfates, with cardiopulmonary and lung-cancer deaths contributing to the pattern. This is a relative population comparison, not a 26-percentage-point increase in anyone’s personal probability of dying.
What it cannot establish
This was an observational cohort, not a randomized experiment. Adjustment reduces some differences between participants but cannot eliminate unmeasured confounding. City-level pollution measurements also cannot describe every participant’s exposure at home, at work or while travelling.
How to use this evidence
The study helps explain why reducing exposure over time matters. It does not define a safe number of minutes outdoors, compare today’s neighbourhood routes or diagnose harm in a particular person. For a decision today, combine current local information with applicable public-health guidance.
Sources
Educational information; personal health questions belong with your clinician.
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