http://rpuchalsky.home.att.net/sci_env/dixy_1.txt
7. Volcanoes and Stratospheric Chlorine
We now come to the notorious claim that volcanic eruptions are major sources of stratospheric chlorine. Fifteen years ago this was a defensible hypothesis. Volcanic gases _are_ rich in Hydrogen Chloride, HCl, and very large eruptions can in principle inject these gases directly into the stratosphere. It is well known that they do inject large quantities of sulfur dioxide; whether they inject chlorine as well is a question that must be resolved by observation. Such observations have been carried out for El Chichon, the largest eruption between 1956 and 1991, and for Pinatubo, the largest eruption since 1912, and in both cases large increases in stratospheric chlorine were not found. El Chichon injected ~40 ktons of HCl into the stratosphere [Mankin and Coffey], while Pinatubo produced considerably less [Mankin et al.] CFC emissions, on the other hand, result in an annual flux of 300 ktons of Cl into the stratosphere. The long-term record of total stratospheric chlorine shows a steady increase with time, rather than a series of steps following major volcanic eruptions [Rinsland et al.] Finally, major volcanic eruptions can be detected as sulfur spikes in ice core records. These same cores show no corresponding chlorine spikes, not even for the enormous eruption of Tambora in 1815 [Delmas]. Indeed, the scientific question is not whether volcanoes deliver large amounts of chlorine to the stratosphere, but rather why they do not do so. Model calculations suggest that the HCl is dissolved in condensing water vapor (there is ~10,000 times as much water as HCl in a volcanic plume) and removed in the heavy rains that usually follow an eruption before it can be dispersed in the stratosphere [Pinto et al] [Tabazadeh and Turco]. Whatever the explanation, direct measurement has shown that *volcanoes are not major sources of stratospheric chlorine*.
Turning to _Environmental Overkill_, we find that none of the recent work is even mentioned. Only a single paper, published in 1980, is cited, and this one is blatantly misrepresented:
p. 35: '...David A. Johnston (who died at Mt. St. Helens), in a posthumously published paper (Science, July, 1980), brought many previous estimates up to date and refined the measuring techniques for chloride in volcanic emissions. He pointed out that a single eruption of Mount Augustine in Alaska in 1976 put more chlorine into the stratosphere than was contained in the worldwide production of CFCs for the entire year 1975.'
Johnston says no such thing. From the abstract of his paper:
'Degassing of ash erupted during 1976 by Augustine Volcano in Alaska released 525 x 10^6 kilograms of chlorine (+- 40%), of which 82x10^6 to 175x10^6 kilograms may have been ejected into the stratosphere as hydrogen chloride. This stratospheric contribution is equivalent to 17 to 36 percent of the 1975 world industrial production of chlorine in fluorocarbons.' [Johnston]
Two things to note: first, Johnston did not measure the chlorine contribution _in the stratosphere_; rather, he estimated it from the total chlorine production. Many such estimates were published during the 1970's, and because different workers made different assumptions about what fraction of the chlorine produced actually reached the stratosphere, the results varied widely. Johnston was one of those who believed that the fraction was large. Direct measurements, cited above and ignored in _Environmental Overkill_, have shown him to be wrong. Second, even Johnston's overestimate does not support the claim that the volcano's contribution to stratospheric chlorine amounted to *more* than a year's worth of CFC production - instead, Johnston said 17- 36%. As I will discuss below, it is very likely that the authors never examined Johnston's paper, relying instead on an unreliable secondary source.
Similar criticism applies to the statements about Mt. Erebus:
p. 34: '...Mt. Erebus in Antarctica has been producing 1000 tons of chloride daily since 1972. Mt. Erebus is located 10 kilometers upwind of McMurdo Sound, where ozone measurements are made. The volcano pumps out 50 times more chlorine annually than an entire year's production of CFCs.'
To begin with, Mt. Erebus has _not_ been producing 1000 tons of chloride daily since 1972. Measurements in 1986 indicated that it was producing about 100 tons per day; the researchers then estimated that during a more active period between 1976 and 1983 the volcano's output did reach 1000 tons per day. [Kyle et al.]
Let us, however, proceed on the assumption that the quoted figure is correct. 1000 tons/day is 365 kton/year, which is nowhere near 50 times the chlorine contained in a year's CFC production; it's more like about 50% [Wayne, p. 167]. Oddly enough the book gives an approximately correct figure for industrial production, ~750,000 tons Cl, on the very same page; the authors appear to have lost a factor of 1000 in their arithmetic. But more importantly, Erebus is _not_ an explosively erupting volcano. Even in the active period it was about 4 orders of magnitude weaker than Mt. Pinatubo, and the plume never came near the stratosphere; most of the time it just crawls over the crater rim (where the chlorine measurements were made.) It is just one more source of water-soluble HCl, and is ruled out by the arguments given previously for sea salt spray (which in fact is a much larger source than all volcanoes put together).
Furthermore, if chlorine from Mt. Erebus were responsible for the antarctic ozone hole one would expect that the *total* amount of chlorine over antarctica would be much higher than elsewhere in the stratosphere. This is not observed. Rather, during the Antarctic Spring all of the chlorine is in the form of radicals that can destroy ozone. Elsewhere, most of the chlorine is bound up in 'reservoir compounds' such as HCl and ClONO2.
(Note: It has recently been found that the 1986 measurements were too large [Zreda-Gostynska et al]; the true figure for 1986 should be 19 tons/day (or 7 ktons/year) and the estimate for 1976-83 is now 167 tons/day (61 ktons/year.) This paper was published after _Environmental Overkill_, so the authors cannot be held responsible for it; nevertheless they did misrepresent the information that was available at the time of
