Class

Meaning

Classification

I

maximum ambient air pollution levels of all substances monitored are less or equal to one half of IH_x limit values

clean to almost clean air

II

a substance�s ambient air pollution level is greater than 0.5 IH_x but no limit value has been exceeded

moderately polluted air

III

a substance�s limit value has been exceeded, other substance�s ambient air pollution levels are less or equal to 0.5 IH_x

polluted air

IV

a substance�s limit value has been exceeded, some other substance�s have ambient air pollution levels > 0.5 IH_x, but � IH_x

strongly polluted air

V

more than one substance�s limit value has been exceeded

heavily polluted air