BACKGROUND. Air pollution is considered a major risk factor for airway infections, with Streptococcus pneumoniae (the pneumococcus) causing most cases. Although epidemiological data strongly suggest an association between air pollution levels and the transmission of respiratory pathogens, direct causal evidence is lacking, and the underlying mechanisms remain poorly understood. METHODS. To address this gap, we used a novel murine host-to-host transmission model to assess the impact of two prevalent sources of air pollution (Diesel exhaust particulates [DEP] and rail dust) on pneumococcal transmission and colonisation dynamics. In this model, mice were exposed daily to 15-30 µg of DEP or rail dust, representing typical daily human exposure in urban environments. RESULTS.  We demonstrate that air pollutants facilitate pneumococcal transmission in a dose- and type-dependent manner. Air pollution exposure increased host susceptibility to pneumococcal colonisation and significantly enhanced bacterial shedding from colonised hosts. Further investigation into the underlying mechanisms revealed that air pollutants induce inflammation and mucus production, leading to enhanced nasal secretion and bacterial release from the airways. CONCLUSION. This study provides the first direct evidence that air pollution exposure drives host-to-host transmission of respiratory pathogens and identifies host factors that may be targeted to mitigate the impact of air pollution on respiratory infections.