Environmental Engineering Reference
In-Depth Information
CHAPTER
15
Acid Rain
Gene E. Likens
Cary Institute of Ecosystem Studies, Millbrook, NewYork
I knew that the rain in the White Mountains of New Hampshire was acidic from the very
first sample my colleague, Noye Johnson and I collected during the summer of 1963 at our
research site at the Hubbard Brook Experimental Forest (HBEF). This rain sample had a pH
of 3.7! But, I didn't know why the rain was so acidic—greater than 40 times more acidic than
we thought it should have been (distilled water in equilibrium with CO
2
in the atmosphere
would have a pH of 5.6)—or whether this finding was some unusual feature of the White
Mountains, or whether it was unusual for the eastern United States. The samples of
precipitation (rain and snow) that we continued to collect throughout the year for the next
several decades as part of our larger research program on watershed ecosystems were simi-
larly acidic. (The most acidic value we have measured for a rain storm at HBEF was pH 2.85).
This simple research finding formed the basis for a major conundrum that would have
significant ramifications for ecosystem science and national policy related to air pollution.
Setting out to measure the acidity of precipitation was not an original goal of my research,
but was a serendipitous discovery emanating from a more comprehensive ecological and
biogeochemical study of a forest landscape, which focused on quantifying all inputs and
outputs to watershed ecosystems of the HBEF (
Bormann and Likens 1967
). Many important
findings in science are the result of serendipity, which requires keeping your eyes, ears, and
mind open to unusual events and then jumping quickly to find out what they mean.
It wasn't until I changed jobs in 1969, moving from a faculty position at Dartmouth
College to one at Cornell University, and set up stations to collect precipitation around the
Finger Lakes in New York state, that I discovered that the rainwater in New York had
about the same acidity and chemistry as it did in New Hampshire (
Likens 1989
). This
similarity was our first clue that acid precipitation might be a regional problem. There
essentially were no other similar data for comparison. A serendipitous meeting and con-
versation with Svante Od´n in Sweden during October 1969 greatly intrigued me and
enriched my understanding of the potential for regional air pollution to affect precipitation
