Forests in Decline

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And why are geochemists so speculative about the chemistry of acid rain? Well, to give just one example, looking for hydroxyl radical is far more difficult than looking for a needle in a haystack. Each OH+ molecule exists for only a few thousandths of a second, and it's so rare that the detection level is only a few parts per quadrillion. That's the equivalentoftrying to find one particular hair on all the heads on earth.

To make matters worse, not all acidic products fall as rain, snow, or fog. Some formparticles or attach themselves to other particles and fall as dry deposition. Unfortunately, this process isn't even as well understood as the chemistry of acid rain. How much falls as dry deposition? Nobody knowsfor sure, because no one has yet figured out a good way to measure dry deposition. A common guess, however, is that maybe as much as 40% of the acidic products fall as dry material.

So when you read or hear that there's just not enough known about acid rain to say exactly what needs to be done and what the effects of applying certain controls would be, you can believe it. Yes, more research needs to be done. Most scientists would agree, however, that cutting SO 2 and NO x emissions would reduce acid rain significantly.

[3] Despite those uncertainties, we know that acid deposition does make it to the ground, and it does have effects on living things. The article that this sidebar is attached to describes some of the evidence concerning the effects of acid precipitation on trees. There are also thousands of lakes in the U.S., Canada, and Sweden that have died as their waters have become more acidic. By death, we mean that about the only thing that lives in the water is filamentous algae. To go along with the death of lakes, there's a huge collection of circumstantial evidence linking episodes of highacidity water (from rains and snowmelt) to massive fish kills. Watch out, though: The Ph.D.'s aren't too sure just why a stream full of trout would be done in by a low-pH summer shower. Aluminum may be the culprit, since acidic water mobilizes the toxic metal from soil and rock. Once again, however, the boundaries of modern science stop before this can be proven. Measurement techniques aren't yet up to distinguishing between harmful and innocuous forms of aluminum in water.

No, the exact effects of acid rain aren't understood. But one glance at the forests and lakes downwind from the International Nickel smelter near Sudbury, Ontario, or at any one of the several hundred dead lakes in the Adirondacks, will convince you that there are effects . . . disastrous ones.

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