The study paired personal particulate monitors with 24-hour accelerometry across 304 days in 67 UK adults aged 50-85, and used mixed models to relate within-person deviation from usual PM exposure to next-day movement. Higher-than-usual PM2.5 was associated with 8 minutes less light physical activity (95% CI -14 to -2) and 483 fewer steps (-855 to -82); PM10 showed a similar pattern plus 8 minutes more sedentary time. There was no association with moderate-to-vigorous activity, and no association at all when area-level PM estimates replaced personal monitor readings.
Why it is interesting: Area-level pollution estimates detected nothing that personal monitors did, which bears on how short-term exposure-behaviour associations are measured at all.