City air is quietly shaving millilitres off healthy lungs

Most of what we know about air pollution and lungs comes from people with asthma or other respiratory disease, while the effect on healthy adults has been far less established. Particulate matter, the fine mix of solids and droplets suspended in outdoor air, is something almost everyone breathes every day, so even a small average effect would touch an enormous number of people. Lung function, measured as the volume of air forced out in one second, is a core marker of respiratory health. This review set out to quantify how outdoor particulates relate to that measure in adults whose lungs are healthy.

The researchers systematically searched for studies containing data on outdoor particulate matter levels, either PM10 or PM2.5, alongside measurements of forced expiratory volume in one second in healthy adults. In total, 27 effect estimates from 23 studies met the criteria and were pooled. Acute exposures over days were typically assessed with the finer PM2.5, while long-term exposures were mostly represented by the coarser PM10. Short-term and long-term effects were quantified separately using random effects models, which allow for differences between the studies being combined.

A 10 µg/m3 increase in short-term PM2.5 exposure was associated with a 7.02 mL reduction in FEV1. For long-term exposure, a 10 µg/m3 difference in PM10 was associated with an 8.72 mL annual change in FEV1 and an absolute difference of 71.36 mL. Both acute and long-term exposure therefore pointed in the same direction, towards lower lung function in healthy adults. The authors note that residual confounding from other risk factors, such as smoking, may explain some of the long-term effect.

The relationship between particulate pollution and lung function in people with respiratory disease has been studied extensively, but this review addresses the gap for healthy adults, where the picture was not well established. By pooling across many studies it strengthens the case that the association is real rather than a quirk of any single dataset. It also leaves clear open questions: the long-term effects of the finer PM2.5 and the short-term effects of PM10 remain under-studied, and the authors suggest the two may work through different biological mechanisms. Whether these small average changes translate into meaningful disease risk over decades is not answered here.

This is a reason to think of air quality as part of respiratory health even if your lungs are perfectly healthy. The average changes are small, measured in millilitres, but they appeared across ordinary healthy adults rather than only vulnerable groups, and they tracked pollution over both days and years. Since these are associations rather than controlled experiments, causation is not proven, and smoking may account for part of the long-term picture. Still, it is useful context for anyone who checks air quality readings or trains outdoors in polluted cities.