There are currently no high pollution episodes.

An environmental episode with high air pollution is a situation in which the atmospheric conditions are unfavourable for dispersion and ventilation, meaning that the concentration of a pollutant can increase so much that it may exceed the threshold values established by the legislation. When one of these situations occurs, the most affected areas are usually urban and densely-populated ones, due to the high levels of emissions, chiefly from road traffic. Specifically, a special zone to protect the atmospheric environment has been declared in the conurbation of Barcelona, which includes 40 municipalities, for nitrogen dioxide (NO2) pollutants and suspended particles with a diameter shorter than 10 microns (PM10).

Three scenarios may occur in this situation:

• preventive notice
• declaration of an environmental episode due to high pollution without any traffic restrictions
• declaration of an environmental episode due to high pollution with traffic restrictions (only activated by the NO2 pollutant)

The preventive notice is the phase prior to a potential declaration of an environmental episode and envisages moderate levels of the above-mentioned pollutants, without the environmental episode necessarily occurring, and it therefore seeks to inform the population on a preventive basis. In contrast, the declaration of an environmental episode due to high pollution may occur when the pollution levels are expected to exceed the threshold values established for the next 48 hours (as is the case of a declaration of an environmental episode due to high pollution with traffic restrictions), or when the values defined in each case at more than one station are exceeded for the different pollutants, accompanied by a persistent anticyclonic meteorological situation that indicates that the levels are remaining stable or increasing.

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