According to preliminary data, the acid pollution, normal and provoked (overload of H₂SO₄ , HNO₃₎ in the conifers soils, provokes a microbiological unbalance unfavorable to the fermentative digestion of the needles litter, leading to disorders at the roots level and disturbance of the acropetal sieve circulation. As for the oxidative pollution, suggestion is made that its ozone destructive regulation, paradoxically insured at night in the cities by NO from the cars, but normally enforced in nature by the denitrifying activity of the microflora (essentially bacteria volatilizing N₂O and NO) is slowed down by the acidic falls, opening the way to direct oxidative lesions on the trees.