Background: Air pollution exposure during pregnancy and childhood has been linked to lung development deficits in children, however, few studies have identified potential windows of susceptibility to air pollution exposure from conception to early childhood on lung function.

Objectives: To identify potential windows of susceptibility to the effects of prenatal and childhood exposure to air pollution and lung function.

Methods: We included 1029 mother-child pairs from the INMA (INfancia y Medio Ambiente) birth cohort. We estimated residential daily NO2, PM10 and PM2.5 exposure during pregnancy and up to the 6 years of childhood. Lung function (forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1)) was assessed through spirometry in children aged between 6 and 8 years. Distributed lag non-linear models were used to identify windows of susceptibility, adjusting for several socioeconomic and lifestyle confounding variables and temporal trends.

Results: Higher NO2 exposure around the 69th month was associated with a reduction in FVC (−2.22 mL; 95 % CI: −4.28 to −0.15) per 10 μg/m3, and around the 60th month with FEV1 (−1.90 mL; 95 % CI: −3.78 to −0.04). Higher PM10 exposure around the 43rd month was associated with lower FVC (−4.11 mL; 95 % CI: −8.30 to −0.20) per 10 μg/m3. Higher PM2.5 exposure around 55th month was associated with lower FVC (−8.87 mL; 95 % CI: −16.51 to −1.22) and FEV1 (−14.93 mL; 95 % CI: −14.93 to −1.63) per 5 μg/m3. No evidence of an association was observed for prenatal exposure to any pollutant.

Conclusions: Our findings suggest that higher exposure to outdoor air pollution (NO2, PM10 and PM2.5), particularly at 3–5 years, was associated with a reduction in lung function. These findings highlight the necessity of exploring the delayed effects of air pollution exposure in the development of future health outcomes and detrimental effects.