In September 2021, the World Health Organization (WHO) released updated global air quality guidelines (AQGs) for the first time since 2005. Incorporating a wealth of interim evidence demonstrating the adverse health effects of air pollution, the WHO tightened recommendations for target air pollution concentrations, including lowering the AQG for fine particulate matter (particulate matter ⩽2.5 μm in aerodynamic diameter [PM_2.5]) from 10 μg/m³ to 5 μg/m³ (1). These updated guidelines not only emphasize the global urgency of improving air quality to prevent illness and death but also send the message that harmful effects occur even at lower concentrations of air pollution.

On the heels of these more stringent recommendations, in this issue of AnnalsATS, Takebayashi and colleagues (pp. 763–772) investigated the association between concurrent exposure to low concentrations of PM_2.5 and lung function growth over 4 years in a large cohort of 1,466 pre- and early adolescent school children across 10 cities in Japan (2). Exposure measurements captured continuous ambient PM_2.5, ozone (O₃), and nitrogen dioxide (NO₂) concentrations at or near each school and were characterized by relatively low overall annual mean PM_2.5 concentrations of 13.5 μg/m³. Perhaps counter to the sense that air pollution—even at lower thresholds—is harmful to lung health, the authors found no significant associations between PM_2.5 at these concentrations and lung function growth over the study period in models adjusted for confounders and copollutants.

These results are in contrast to previous literature demonstrating adverse effects of higher PM_2.5 concentrations (>20 μg/m³) on longitudinal childhood lung function trajectories (3), as well as corresponding improvements in lung function with reduced exposure to air pollution during adolescence (4).

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