ACID RAIN 13
REMOTE SITE PH DATAAcid precipitation is also being measured at remote sites.
pH data for more than 1700 daily or three-day samples
collected in the Hawaiian Islands were reported by Miller
and Yoshinaga (1981). The observed pH for the Hawaiian
samples ranged from about 3.6 to 6.0. The average pH for
about 800 daily samples collected at three sites in the Hilo,
Hawaii area was 4.7. The pH decreased with altitude, with
an average pH of 4.3 for 92 samples collected at a site at
an altitude of 3400 meters. To check for the possibility of
local volcanic emissions being the dominant source, samples
were collected on the island of Kauai, which has no volcanic
emissions and is 500 km north of the big island of Hawaii
where all the other sampling took place. For the Kauai site,
the average pH was 4.79, which is similar to the pH for the
Big Island.
Galloway et al. (1982) have measured the chemistry of
precipitation for several sites remote from manmade pol-
lution. An important feature documented by these inves-
tigators is that the pH of samples from these remote sites
increased significantly between the time of field collection
and the time of sample receipt at the laboratory in Virginia.
However, the pH of the samples remained stable when a
chemical was added to stop bacterial activity in the samples.
It was established that organic acids (from natural sources)
are an important acid component in samples from the remote
sites and without the pH stabilization procedure, the organic
acids were lost during shipment and only the strong mineral
acids and the elevated pH values were detected. For three
remote sites in Australia, in Venezuela, and on Amsterdam
Island, the weighted average pH values for stabilized sam-
ples were 4.8, 4.8, and 4.9 respectively.
The detection of acid rain at locations remote from man-
made pollution has led researchers to suggest that departures
of precipitation pH below 5.0, instead of the commonly
used level of 5.6 or 5.7, would better indicate the local and
regional manmade modulations to the natural global back-
ground. That is, perhaps we should define acid rain to be
samples where pH is less than 5.0. However, since pH is in
fact the balance of a group of ions, it is scientifically better to
use the levels of these ions, and not just pH, to characterize
samples as acid rain.RECOMMENDATIONS FOR THE FUTUREThis discussion has focused on results of wet deposition
measurements. However, both wet and dry deposition must
be measured so that eventually a mass balance can be evalu-
ated to account, year by year, for the pollutants put into the
air. Therefore:1) Wet deposition measurements across the United
States should be continued indefinitely, just as we
continue to monitor emissions, air quality, andweather variables such as precipitation amount
and type, and
2) Dry deposition measurement techniques need
continued development and evaluation, and a
long-term monitoring network must become
available to provide data for calculating total
deposition (wet and dry).REFERENCESBowersox, V.C. and G.J. Stensland (1985), Seasonal patterns in the chem-
istry of precipitation in the United States. In Proceedings of the 78th
Annual Meeting, Air Pollution Control Association, Pittsburgh, PA,
Paper No. 85–6.A.2.
Cogbill, C.V. and O.E. Likens (1974), Acid precipitation in the northeastern
United States. Wat. Resources Res., 10 , 1133–1137.
Evans, L.S., G.R. Hendrey, G.J. Stensland, D.W. Johnson, and A.J. Francis
(1981), Acidic precipitation: considerations for an air quality standard.
Water, Air, and Soil Pollution, 16 , 469–509.
Galloway, J.N., G.E. Likens, W.C. Keene, and J.M. Miller (1982), The com-
position of precipitation in remote areas of the world. J. Geophys. Res. ,
87 , 8771–8786.
Gillette, D.A., G.J. Stensland, A.L. Williams, P.C. Sinclair, and T.Z. Marquardt
(1992), Emissions of alkaline elements calcium, magnesium, potassium,
and sodium from open sources in the contiguous United States. Global
Geochemical Cycles, 6 , 437–457.
Gorham, E. (1958), Atmospheric pollution by hydrochloric acid. Quart. J.
Royal Meterol. Soc., 84 , 274–276.
Granat, L. (1972), On the relationship between pH and the chemical compo-
sition in atmospheric precipitation. Tellus, 24 , 550–560.
Junge, C.E. (1963), Air Chemistry and Radioactivity. Academic Press, New
York, 382 pp.
Likens, G.E., F.H. Borman, R.S. Pierce, J.S. Eaton, and R.E. Munn (1984),
Long-term trends in precipitation chemistry at Hubbard Brook, New
Hampshire. Atmos. Environ., 18 , 2641–2647.
Lynch, J.A., V.C. Bowersox, and J.W. Grimm (1996), Trends in precipita-
tion chemistry in the United States, 1983–94: An analysis of the effects
in 1995 of phase I of the Clean Air Act Amendments of 1990, Title IV.
Open-File Report 96-0346 ( http://h20.usgs.gov/public/pubs/acidrain ),
U.S. Geological Survey, Reston, VA.
Lynch, J.A., J.W. Grimm, and V.C. Bowersox (1995), Trends in precipita-
tion chemistry in the United States: A national perspective, 1980–1992.
Atmos. Environ., 29 , 1231–1246.
Miller, J.M. and A.M. Yoshinaga (1981), The pH of Hawaiian precipitation—
A preliminary report. Geophys. Res. Letters, 7 , 779–782.
National Acid Precipitation Assessment Program (1990), Acidic Deposi-
tion: State of Science and Technology, Volumes I–IV, Supt. of Docu-
ments, Government Printing Office, Washington, DC.
National Acid Precipitation Assessment Program (1991), The U.S. National
Acid Precipitation Assessment Program 1990 Integrated Assessment
Report, NAPAP Office, Washington, DC, 520 pp.
National Research Council (1986), Acid deposition—long-term trends.
Wash. DC, National Academy Press, 506 pp.
Reuss, J.O. (1975), Chemical/Biological Relationships Relevant to Ecologi-
cal Effects of Acid Rainfall. U.S. EPA Report EPA-660/3-75-032, 46 pp.
Seinfeld, J.H. (1986), Atmospheric Chemistry and Physics of Air Pollution.
John Wiley & Sons, New York, 738 pp.
Smith, R.A. (1872), Air and Rain: The Beginnings of a Chemical Climatol-
ogy. Longmans, Green, and Co., London, England.
Stensland, G.J. and R.G. Semonin (1982), Another interpretation of
the pH trend in the United States. Bull. Amer. Meteorol. Soc., 63 ,
1277–1284.OTHER GENERAL REFERENCESGraedel, T.E. and P.J. Crutzen (1993), Atmospheric Change—An Earth
System Perspective. W.H. Freeman and Company, New York, 446 pp.C001_001_r03.indd 13C001_001_r03.indd 13 11/18/2005 10:07:28 AM11/18/2005 10:07:28 AM