There are monitoring stations distributed throughout Barcelona and they constantly measure the main atmospheric pollutants which can affect people's health. The data from these stations, together with other weather and physicochemical dispersion models, are processed by computer and provide an approximation of the real level of pollutants at every point in the city.
In terms of its technical requirements, the measuring station system is standardised under European Union regulations, which is the standard used by cities at the forefront of environmental control.
Once recorded, the specific data provides daily, monthly and annual analyses. You can use this link to consult the evolution of both hourly and historical data.