The possibility of assessing and predicting the concrete damage is essential in order to apply an adequate and accurate maintenance and reparation policy for infrastructure management. In urban tunnels, concrete is exposed to pollutant emissions from the engines of the vehicles which can cause neutralization issues that may lead to the corrosion of the steel reinforcement. As pollutant concentration is an indispensable parameter to evaluate and forecast concrete neutralization damage, the aim of this work was to quantify gas concentrations inside an urban tunnel based on available traffic intensity data. This study was carried out performing in-situ concentration measures, comparing these values with available traffic data during the same period and developing a traffic intensity study to obtain the total concentrations at which the infrastructure had been exposed since its construction. This analysis was performed in a ventilation gallery of the Madrid Calle 30 tunnels as a part of a study in development with the aim of determining the service lifespan of the structure based on a predictive numerical model for concrete carbonation.