This paper examines the effects of prenatal exposure to fine particulate matter (PM2.5) on birth outcomes in a low-pollution setting. Using linked administrative data on births and air quality in Quebec (2008-2015), we compare infants exposed to different pollution levels within the same neighborhoods and time periods to account for socioeconomic and seasonal differences. We find no significant effects at the population level, but exposure increases the risk of low birth weight and preterm birth among female infants and children of less-educated mothers. These findings suggest that even in low-exposure environments, current air quality standards may not sufficiently protect vulnerable populations. Strengthening pollution advisories for pregnant women and refining regional air quality policies could help mitigate these risks.