ObjectivesEnvironmental exposure to chemicals has been considered a potential factor contributing to deteriorated semen quality. However, previous literature on exposure to air pollution and semen quality is inconsistent. We therefore investigated the health effects of short-term and long-term exposure to fine particulate matter (PM_2.5) on semen quality in Taiwanese men from the general population.MethodsA cross-sectional study was conducted among 6475 male participants aged 15–49 years who participated in a standard medical examination programme in Taiwan between 2001 and 2014. Semen quality was assessed according to the WHO 1999 guidelines, including sperm concentration, total motility, progressive motility and morphology. Three-month and 2-year average PM_2.5concentrations were estimated at each participant’s address using a spatiotemporal model based on satellite-derived aerosol optical depth data. Multivariable linear and logistic regressions were used to examine the associations between PM_2.5and semen quality.ResultsA robust association was observed between exposure to PM_2.5and decreased normal morphology. Every increment of 5 µg/m³in 2-year average PM_2.5was significantly associated with a decrease of 1.29% in sperm normal morphology and a 26% increased risk of having the bottom 10% of sperm normal morphology, after adjusting for a wide range of potential confounders (p<0.001). On the other hand, an increment of 5 µg/m³in 2-year average PM_2.5was associated with an increase of 1.03×10⁶/mL in sperm concentration and a 10% decreased risk of being the bottom 10% of sperm concentration (both p<0.001). Similar results were found for 3-month PM_2.5.ConclusionsExposure to ambient PM_2.5air pollution is associated with a lower level of sperm normal morphology and a higher level of sperm concentration.