(28)An alert threshold and an information threshold for sulphur dioxide, nitrogen dioxide, particulate matter (PM 10 and PM 2,5 ) and ozone should be set for the protection of the general population, and especially sensitive population and vulnerable groups, from brief exposures to elevated concentrations of pollutants. Those thresholds should trigger the dissemination of information to the public on the associated health risks of exposure and the implementation, where applicable, of short-term measures to reduce pollution levels where the alert threshold is exceeded.