Roadway tunnels: A critical review of air pollutant concentrations and vehicular emissions

Air quality is a widespread problem with the presence of pollutants in indoor and outdoor environments that generate significant consequences for the population, ecosystems and exposed materials. Vehicular traffic is one of the main sources of air pollutants and, therefore, needs to be studied and analysed in detail. This review reported the results of studies conducted on tunnels, in particular for the measurement of concentrations and the definition of emission factors. The characteristics of the tunnels, available ventilation systems, type of vehicular traffic, and geographical distribution, in addition to concentrations and emission factors, are discussed. Light-duty vehicles are the most frequent category in the case studies. Between the fuels used, gasoline is by far the most widespread. Pollutant concentrations concentrations can reach very high levels. For example, atmospheric particulates (with an aerodynamic diameter of 10 µm) and nitrogen dioxide have also reached levels of 1490 µg/m3 and 4982 µg/m3, respectively.