Pollution control is based on correctly measuring pollutant concentrations but, at the moment, the main European cities only monitor pollution levels by means of a few fixed stations co-located in selected points of the urban layout far from hot-spots and/or by means of meteorological prediction models of future pollution. Few cities integrate the information from both sources, aimed at attaining online control of traffic flows, as these can cause emergency episodes related to pollution levels when surpassing legal thresholds.

The main handicaps to date have been the lack of reliability of the prediction models used, as well as the difficulty of making precise online measurements of urban "hot-spots”.

Air quality control is currently restricted to the collection of meteorological and pollutant concentration data at several fixed stations sometimes located far from "hot-spots”. On rare occasions, such a control incorporates real density or traffic flow data from those spots, and it therefore becomes unfeasible to deduce any empirical causal relationship between the data gathered and traffic in the "hot-spots”. On the other hand, many cities have developed air quality prediction models based on real or estimated data referring to traffic and car emissions, as well as to weather forecasts, producing mid-term predictions (meso-models for 24 to 72 hours) which are difficult to contrast empirically against live measures from fixed measurement stations. The relevance of such models is scarce in practice, since they are not used to take traffic management control measures in most cases, but as a forward indicator of high pollution episodes. It is evident that departments in charge of urban mobility cannot integrate in their traffic management models predictions that are difficult to compare with real time data, as their decisions are based on instant mobility data in particular.

The availability of more precise and shorter-term prediction models based on live traffic and car emission data referred to the real vehicle traffic conditions, as well as the recent appearance on the market of a wide range of measurement tools for the different contaminating agents which are far less expensive than those used in fixed stations, together with today’s communication systems technology, means that a large amount of online pollution measurements corresponding to the "hot-spots” within the city are now available.

When comparing these measures with the predictions from a shorter than usual term model (3 to 5 hours), it is possible to predict some hours in advance, and with a high degree of reliability, the high pollution occurrences for different places of all urban areas, as well as to draw up alternative scenarios based on simulated traffic flow deviations or restrictions, across those or nearby areas which influence them.

In this way, the current urban traffic management and control system would have at its disposal another absolutely reliable decision element, complementary to the traditional mobility and accessibility decision algorithms, which would help to develop a more rational and environmentally friendly management of traffic flows as it is based on live surveillance.

The application of the current legislation regarding air quality conditions in cities, which compels them to draw up Air Quality Plans for several forthcoming years, will therefore provide another management tool that will undoubtedly contribute to improving the air breathed by citizens and act upon the most important urban contaminating agent (i.e. traffic) by organizing traffic flows following the "ecological capacity” of the city corresponding to each weather condition, thus allowing only sustainable flows through the "hot-spots”.