When designed and operated adequately, natural ventilation (NV) can improve the buildings' energy efficiency and indoor environmental quality. There is a plethora of factors that limit the effectiveness of NV, such as the climate, surrounding buildings, noise, and ambient air pollution, especially in urban environments. Nevertheless, the existing NV potential (NVP) calculation methods are complex and difficult to be used. This study proposes a new methodology for quantifying the NVP by considering the exterior climate and ambient air pollution. This methodology analyzes climatic and ambient air quality data to estimate the NVP of urban and suburban sites of 27 European cities. The results reveal that the level of urbanization and proximity to traffic significantly influence the applicability of NV. Taking ambient air pollution into account reduces the climatic NVP on average: 11% for suburban background sites, 28% for suburban traffic sites, 22% for urban background sites, and 50% for urban traffic sites. Building designers can use the proposed methodology in the building design phase in order to implement the NV without increasing occupants' exposure to outdoor air pollution. The results of the statistical analysis can be used by the public authorities and the decision-makers to better consider the limitations and opportunities of the NV use by the building stock.