Jekyll Island meeting report James Galloway compares acid deposition in remote areas with that found in industrialized areas
In May 1985, the 15th Annual Symposium on the Analytical Chemistry of Pollutants convened in Jekyll Island, Ga. As part of the meeting, a series of lectures on acid deposition was presented. In the past two months, we have reported on the lectures given by Courtney Riordan of EPA and George Hidy of the Desert Research Institute. This month, we conclude this series of Views with a report of the lecture given by James Galloway of the University of Virginia. Galloway was one of five scientists chosen in 1983 to advise the White House staff on the problems of acid rain. His involvement in this field goes back to his days of postgraduate research at Cornell in 1974. While there, his task was to develop new analytical techniques or use existing ones to measure inorganic and organic acid concentrations in precipitation in representative areas of the U S . In his opening remarks, Galloway said that a paper in Science, written by John 0. Frohliger and Robert Kane, came to his attention in 1975 (I). The paper’s thesis was that acid deposition can be attributed to a phenomenon of weak acids, including carbonic acid. Galloway found as part of his own research that nitric acid and sulfuric acid were in fact the primary contributors, but that carbonic acid, ammonium ion, and to a certain extent organic acids also contribute to the total acidity of Precipitation. The ecological impact of weak acids, according to his work, was insignificant.
More questions Galloway pointed out that there are a number of questions attendant to the
James Galloway
study of acid precipitation. For instance, although we know that the trends for the past 30 years show that strong acids and, to a lesser extent, organic acids are the causes of free acidity, it might be useful to know what the composition of precioitation was a cenNTY ago. What, in tact, is the natural component of acid in precipitation? The questions go on: What is the exact mixture of acids in precipitation? Is it the same all over the world? How can analytical chemistry be used to help find answers? We know that North American acid deposition is a largely anthropogenic phenomenon caused by the emission of sulfur dioxide and nitrogen oxides to the atmosphere. But does everything that is emitted over the continent fall here? How does North America contribute to the global atmosphere? Since 1979, Galloway and his colleagues at the University of Virginia, in conjunction with Gene Likens of the New York Botanical Garden, have been collecting precipitation at remote sites-such as the southern part of Chile and at Cape Point in South Africa-with two questions in mind: What are the processes that control precipitation in remote areas, and how does the acid composition compare with that found in eastern North America? Gal-
001%993BW85109lS-1157$01.5010 0 1985 American Chemical Sociely
loway said, “Using data from these sites and data from other parts of the world, we were able to determine the rate of [wet and dry] deposition of sulfur and nitrogen compounds to remote continental areas? Wet deposition appears to control the removal bf excesS&lfur from the atmosphere. It appears that emission of dimethyl sulfide from the oceans is the primary source of marine excess sulfur. Galloway said, “In the case of the continerlts, sulfur precipitation is controlled by emissions of hydrogen sulfide and dimethyl sulfide; each of these gases will be converted to sulfuric acid in the atmosphere.” Developments in analytical chemistry have increased our understanding of how sulfur and nitrogen move through remote areas. Galloway said that he is confident that wet deposition figures are good to about a factor of two, but that dry deposition figures may be off by as much as an order of magnitude. There are two kinds of errors involved with dry deposition measurements. Galloway said, “We don’t know how fast something comes out of the atmosphere-this is a microphysical problem-and we don’t know the species and their .concentrations. Further, for some species we don’t have the sensitivity to measure naturally occurring concentrations.” How bad is acid rain in eastern North America? How does it compare with that in remote areas? According to Galloway, it is clear from the data that there is a substantial difference in the composition of precipitation between eastern North America and other parts of the world (Figure 1). Another interesting aspect of these Environ. Sci. Techml.. MI. 19. NO. 12. 1985 1157
data is that throughout the world the concentration of excess sulfate in precipitation is remarkably similar. The mean concentration of sulfate is 5.5 MIL, and the standard deviation is 1.5 peq/L.Galloway explained that he and two colleagues published research in 1984 showing that average annual concentrations of sulfate in precipitation are about 16 times greater in developed areas than in remote areas (2).
Surprising finding During the course of their investigations and analyses of precipitation from remote areas, the researchers made an interesting-if accidental-discovery. Galloway said that when the project was being designed, he and Gene Likens published a paper “that said you don’t need to add a biocide to precipitation to maintain its chemical composition [3]. Why? Because in eastern North America, the precipitation is stable in composition because of the high acidity. But we were not sure of the composition of the r e m e areas.lust to be on the safe side, we added chloroform to an aliquot of precipitation.” The protocol for the site operator in the remote areas beiig studied was to take a rain sample using clean collectors, to divide the sample in two aliquots, and to put chloroform in one aliquot. These samples were then returned to the researchers for chemical analysis. 1158 Environ. Sci.Technol., Vol:lO.
No. le, is95
Galloway said, “When we looked at the data for the chloroform samples, the laboratory pH measurements in all Cases were identical to pH measurements made at the field collection site, within 0.2 pH units. But for the samples without the chloroform addition, the field pH was lower than the lab pH. When we started looking at the data, we found that the ion balances of the samples without chloroform were always very good, the cations equaled the anions.” Although there was no change in pH for the chloroformed samples W e e n the field and lab analyses, the ion balances were always off; there were always more cations than anions. Gall* way said, “We began to wonder what could be happening. William Keene of our laboratory came up with the hypothesis that there is some activity in the sample”; something that was b i e logically useful was beiig consumed. The candidate was organic acids. “We discovered that formate and acetate were in the rain samples. We also found that there were enough of these organic acid anions in the chloroformed samples to account for any changes in pH.” The researchers began a series of lab experiments to see whether biological activity could account for losses of formate and acetate in rain samples. This was the definitive experiment for the chloroform samples.
This observation, in addition to other experiments on the stability of formate and acetate with and without chlom form, proved that microbial activity was causing the decrease in formate and acetate and the increase in pH.
Role of organic acids Galloway then turned his discussion more to the issue of organic acids. He said, ‘‘I view myself as a detective using chemical clues. And this organic acid contribution to the acid deposition story is in fact a detective story. We made some initial analytical chemical measurements on environmental samples. We noted the discrepancy between pH in the fEld and laboratory samples. Either we were doing something wrong or there was somethiig about the natural system that we did not understand. Using analytical chemistry, we discerned the importance of organic acids and resolved the problem.” Galloway explained that the researchers’ aim was to understand the connection between the composition of precipitation and its effects on various receiving system.He said, “We need to understand the linkage between the chemical and the biological.” For the past two years, Galloway and his coworkers have been studyiig m i m r g a nisms in the atmosphere and in precipitation to see whether they could pinpoint the role of bacteria and fungi
The acid deposition at this site in.southern Chile comes mainlyfrom organic acids
emitted to the atmosphere, only 50% falls in eastern North America. Galloway stated that this figure was arrived at as a result of the Western Atlantic Ocean Experiment in 1981, which studied the flux of sulfur out of eastern North America by atmospheric transport (4). The study sought to answer several questions: Where does the sulfur go? How much falls over the ocean? How much goes to Europe? How much exchange8 with the Southern Hemisphere? Several sampling platforms were used in the study to deternunethe transport of sulfur eastward from North America. They included cruise ships of the Home Lines, which travel weekly between New York, Bermuda, and Nassau. For the past four years, rexarchers have been studying rain collected on hoard the ships. They have measured its chemical composition and gathered data on deposition over the Where it come8 down western Atlantic Ocean. Other platGalloway then turned the focus of the forms are National Oceanic and Atdiscussion to the dispersion of acid in mospheric Administration (NOAA) rethe atmosphere. He said that the stack search aircraft. Last spring N O M S of the copper and nickel smelter in Sud- King Air was used to collect gases and bury, Ont., Canada, is, at 1400 ft, the aerosols between North America and tallest stack in the world, and it emits a Bermuda. In January they will use the few percent of the world’s sulfur to the King Air and the NOAA P3 to investiatmosphere. Galloway said, “This gate transport of gases and aerosols brings up the topic of long-range trans- eastward from North America. port. From an atmospheric sulfur Galloway said that about 4.3 terabudget that Doug Whelpdale, an atmos- grams of sulfur is ejected from North pheric physicist at the Canadian Atmos- America to the atmasphere over the Atpheric Environmental Service, and I lantic Ocean. He said, “From our meaanalyzed, we found two things.” First, surements in Bermuda and on board the the total of North American sulfur ships and aircraft, we estimate that the emissions (US.and Canadian) is about wet deposition of sulfur to the western 16 te.ragrams. Thii quantity is several A h t i c Ocean is about 1.2 teragrams. orders of magnitude higher than the Dry deposition is 0.1 teragrams.” natural contribution of sulfur to the at~d emission of sulfur to the atmosphere of eastern North America. mos~herein the western Atlantic second, of the anthropogenic sulfur c h 3 l l iS about 0.1 “grams. That
in oxidizing organic acids. Another intriguing possibility is that perhaps the micmganisms are. in themselves producing organic acids. Galloway said, “I have this vision of clouds being little biochemical factories that both produce and consume organic acids. Therefore, let’s not forget the biology when we deal with the chemistry.” Galloway once again referred to Frohliger and Kane3 paper showing that organic acids were not a factor in the increasing acidity of precipitation in North America (1). Recent analyses of North American precipitation confvm that research. Although the concuntrations of organic acids in North America and remote areas are about the same, in remote areas, organic acids can control pH, but in the northeastem U.S.H2S04 and HNO, control the pH of precipitation because of their much higher concentrations.
leaves about 3.1 teragrams unaccounted for. This amount is being ejected to the east of Bermuda. A site on the western coast of Ireland has been established to investigate the trans-Atlantic transport Of North American sul-
fur. Finally, Galloway touched on the matter of nitrogen. “We don’t know how much nitrogen is lost from North America by atmospheric transport because we cannot measure it,” he said. “Until we get analytical instrumentation that measures nitrogen dioxide, PAN-peroxyacetyl nitrate, and ammonia at the part-per-trillion level, we will not be able to determine the effect of North American emissions on the global atmosphere. Prognosis
Until scientists can provide convincing data, and explain them, policy makers will be reluctant to make regulations concerning acid deposition. This may he reasonable because although we know how much controls will cost, we are not really sure how effective they will be in reducing sulfur and nitrogei Meanwhile. 20 countries. not including the U.S.’, have subscrihed to a “cleaner air convention,” under which they agree to reduce So, levels by at least 30% by 1993 or 1995. Not until So,emissions are reduced in all developed nations can the acidification phenomenon be reversed.
-
Reperenees
(I) Prohligcr, 1.0.; Kame, R. Science 1915, 189,455-57.
(2) Galloway, 1. N.; Likens, G. E.; Hawley, M. E. Science 1964,226, 829-31. (3) Galloway, 1. N.; Likens, G. E. Ltmol. Occanogr. 1979,24,427. (4) mloway, J. N. et PI. ~ m u u .fiviron. 1981.16, 1677-1700.
Emlmn. Sei. Technd.,Vol. 19. No. 12,1985 1169
