Comparing days within cities
Liu and colleagues analysed daily pollution and mortality in 652 cities across 24 countries and regions. They used city-specific time-series models and combined the results. The exposure measures included PM10 and PM2.5, with the main comparison based on a two-day moving average.
Small relative changes across large populations
A 10 µg/m³ increase in the two-day PM10 average was associated with a 0.44% increase in daily all-cause mortality; the 95% confidence interval was 0.39–0.50%. Cardiovascular and respiratory mortality were also associated with particle concentrations. These are relative changes in population death counts, not an individual’s probability of dying after an outing.
Why this is not a personal exposure clock
City-level monitoring cannot determine each person’s inhaled dose, health history or movements. Time-series adjustment addresses factors such as weather and temporal patterns but cannot prove that every observed death was caused by a measured pollution increase. The result does not identify a universal safe duration outdoors.
Short-term exposure deserves attention
This study addresses a shorter timescale than annual-exposure cohorts. It supports taking pollution episodes seriously while keeping the units and two-day averaging period explicit. Do not substitute its PM10 estimate for PM2.5, a gas pollutant or a three-hour effect.
Sources
Educational information; personal health questions belong with your clinician.
Explore next
- Long-term particle exposure: what a systematic review found
- Air pollution and the heart: what the three-hour finding means
- The Six Cities study: what long-term particle exposure revealed
- ESCAPE: particle pollution and mortality across European cohorts
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