Which pH value is indicative of highly acidic rain?
Rain at pH 4.3 is strongly acidic relative to normal rain, whose pH is near 5.6 because of dissolved carbon dioxide. Since pH is logarithmic, pH 4.3 has about twenty times the hydrogen-ion activity of pH 5.6. Values of 6 or 5.5 are near or only slightly below natural rain acidity, while 7.2 is mildly alkaline. Sound classification links the source, atmospheric fate, exposure route, and mechanism of toxicity rather than relying only on the pollutant's name. Effective management combines cleaner fuels, emission standards, monitoring, urban planning, and protection of populations with high exposu
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology