Discussions 1063

EXPERIMENTAL RESULTS OF THE SO2 TRANSFER IN THE

MEDITERRANEAN OBTAINED WITH REMOTE SENSING DEVICES*

The paper by Zettwoog and Haulet is an interesting contri- bution to the q~ntifi~tion of natural sources of SOz. There are, however, two points which the authors may want to clarify. The first one refers to the absolute speed of the wind at the level of the plume. This is particularly intriguing since wind speed, and direction, usually vary with height and with time. If they refer to the average wind at the plume centreiine, or any other representative level, they should indicate this as well as which criteria they use to define this plume level. Teleanemometry can yield reasonably accurate measure mcnts of plume velocity for isolated stacks, close to the exit, in neutral to stable a~osphe~c conditions. This, however, may not be the situation with plumes which may be influenced by the source, as may happen with a large orographic feature such as a volcano. If entrainment occurs in the wake of the source, the speed of the upper (and well defined) puffs of the plume determined by tel~nemome~y can be quite unre- presentative of an “overall average” speed of the plume, and correspondingly, mass fluxes calculated using the upper winds can be anomalously high, by a factor of two or three, but most likely within the right order of magnitude.

The second question concerns the ground-level values of SO, measured during 26-27 May attributed to the volcano. No mention is made of the location, time or averaging (times)

* Zettwoog P. and Haulet R. (1978) Atmospheric Enuiron- ment 12, 795-796.

for these measurements. Gne suspects that with SoutherlY winds and clear (anticyclonic) weather, the plume could be trapped above the subsidence inversion or, if not (or perhaps, as well as), above any advection inversion over the still rather r&d Mediterranean. In either case, and with this high level of mjsction, the St& plume could travel well inland before being mixed down to ground.

hvironment Canada, M. M. MILLAN Atmospheric Enu~ro~~ Service, Downsuiew, Ontario, Canada M3H 5T4.

AUTHOR’S REPLY

Here is my reply to Dr. Mill&n’s comments. 1. It is true that we are oniy measuring the velocity of puffs

in the centerline of the plume, which is in fact what we need for the flux calculations. In our survey, the puffs were observed many kilometers downstream of the crater, the height of the plume being well stabilized at this distance.

2. Not easily explainable concentrations of SO, from 10 to 40 fig m- 3 have been observed from Reggio de Calabria to Golfo di Pohcastro region. One of many possible expla- nations was that the SO, was originated by the Etna volcano. We have no way to prove this point. We observed that it would be consistent with the wind direction and velocity and with the transfer coefficient which would be 10m9 s me3 for distances greater than 100 km.

Commissariat A L%rtergie Atomique, Department of Protection, Boite Postale 6, 92260 Fo~e~y-A~-Roes, France.

PIERRE ZETT~OOG

SULFATE IN ANTARCTIC SNOW : SPATIO-TEMPORAL DISTRIBUTION*

Delmas and Routron (1978) may have measured sulfate deposition from a major volcanic eruption recorded in Antarctic snow, and this involved concentrations of some 20 x 10e9 g g-t sulfur superimposed on a background of 20 x 10m9g g-t sulfur. They suggest that this type of sulfate ~nt~bution may be superimposed on backgrounds of both marine and anthropogenic contributions in those snows. Their observations define upper limits to contributions of substances to polar snows by volcanic emissions. That is, major eruptions do not contribute more than sporadic additions of sulfate equal in amount to ~ckgro~d con- centrations. In normal polar regions we can assume for the maximum case that half the sulfate is contributed from volcanic sources while the remainder originates from marine

* Delmas R. and Bontron C. (1978) Atmospheric Enuiran- ment 12,123-728.

and anthropogenic sources. On the basis of the sulfate data of Unni et al. (1978) and Herron et al. (1977), this would yield a sulfur concentration of 10 x 10e9 g g-r sulfur from vol- canoes in snow. Herron et al. (1977) claim that titrations of lead in ltltX%vr old arctic snows at levels ofO.05 x 10e9 a g- * are not anthropogenic but originate from natural sour& such as volcanic emissions. The Pb/S ratio in volcanic gas has been measured (Duce et al., 1978) and is found to be c: 1 x lo-’ wt fraction. Tote amount of lead contributed to arctic snow from volcanic sources would therefore be on the order of 1 x 10-r” g g-t lead in snow which is infinitesimally smaller than the concentrations they report to have been derived from natural sources, Such concentrations in fact did not exist in prehistoric times since, concentrations slightly leas than IO-l2 gg-’ lead are observed in 3000-yr old Arctic snow (Murozumi et al., 1969).

Calorie fustfture of Tec~~l~y, C. PAITERSON Division of Geological and Planetary Sciences, Pasadem, CA 91125, U.S.A.

SULPHUR EMISSIONS IN EUROPE* valuable results of the extensive European studies carried out by OECD in the assessment of the long range transport of

The article by Semb is a valuable contribution to our sulfur oxide pollutants over the recent years. knowledge of regional sulfur pollutant emissions. The tabu- It is interesting to note the tabulation of “continuous” and lation offttel data in terms of source area and sulfur content is “variabie” emissions (Table 3) where the ‘*variable” an especially useful contribution because these figures, when component is identified with space heating and thus they are available, have been found, typically, in government presumedly with the colder season of the year. From reports of limited distribution and accessibility. This article Table 2 it would appear that there was a seasonal increase in by Semb also provides the reader with an access to the very sulfur emissions of over 50% from the warm to cold season for

the listed couutries. This is a significant difference between

* Semb A. (1978) Atmospheric Environment 12,455~460. Europe and United States with regard to probable sulfur pollutant emissions because recent data from the U.S.

1064 Discussions

indicate little seasonal change in coal usage throughout the year and thus little seasonal change in sulfur dioxide em- issions in the summer months relative to the winter. Recently in the U.S., discussions of SO2 atmospheric reactions have tended to emphasize the importance of photochemical pro- cesses as major SO, scavenging mechanisms and special importance has been given to the summertime SO, emissions. Thus we might hypothesize, at least qualitatively, that the two major classes of SO1 scavenging processes, liquid droplet and photochemical, would have different degrees of importance in Europe and the U.S. I cannot cite any conclusions from this observation at this time, but since it is not uncommon to translocate air pollution problems, explanations, and sol- utions across the Atlantic the different seasonal emission patterns may be important factors to consider.

The paper by Semb has one feature that, while minor, is in my opinion an unneccessary detraction. That is the attempt at a detailed treatment of biogenic or natural sulfur emissions and to show again that on a regional basis these are unimportant. This conclusion has never been in doubt. We have doubtless passed the time when the material balance approach used in the 1960’s and early 1970’s to approximate biogenic emissions gives us anything new. However, I doubt if we have as yet accumulated enough factual data to make a significantly more accurate estimate of biogenic emissions.

Air Pollution Research Section, College of Engineering, Washington State University, Puhan, WA 99164, U.S.A.

ELMER ROBINSON

AUTHOR’S REPLY Norwegian Institute for Air Research, P.O. Box 130,

The seasonal variation in European emissions of sulphur N-2001 Lillestrbm, dioxide is mainly due to the consumption of fuel and Norway.

electricity for room heating purposes. Since the winter in Northern Europe is also the “dark” season, consumption of electricity for lighting is also larger during this season. Air conditioning in the summer is not common in Europe, its importance in the consumption of electricity in the US may explain much of the apparent difference between the two continents. The higher sulphur content of the U.S. coals and the larger share of coal-fired electric power plant emissions may also beimportant in relation to transformation reactions in the atmosphere.

I certainly agree with Professor Robinson that the esti- mated global emissions of sulphur from natural sources divided by the total area gives a much lower emission intensity than the man-made emissions in the industrialised regions of Europe or North America. However, Europe, with its mere 2% of the global area, has a very high population density, with intensive farming activities and polluted coastal and inland waters. It was therefore rather interesting to find that the first direct measurements of H,S emissions at a tidal flat and marshes in Germany, by Jaeschke (1978), gave such surprisingly low values.

Results from the OECD LRTAP Programme has shown that precipitation from air masses of Atlantic origins contain on the average about 0.8 mg I-’ of excess sulphate. Some of this may be due to natural sources. However, Nyberg’s (1977) results from precipitation samples collected on weatherships in the North Atlantic indicates that a substantial part of this “background value” is due to emissions in North America. In my view, the experience now being gained in the present European and North American investigations of dispersion on the regional scale should also form a valuable basis for more realistic global models.

ARNE SEMB

TOTAL SULFUR AEROSOL CONCENTRATION WITH AN

ELECTROSTATICALLY PULSED FLAME PHOTOMETRIC DETECTOR

SYSTEM*

The article by D. B. Kittelson et al. addresses itself to a very serious pollution problem, i.e. The Determination of Sulfur in the Atmosphere.

The article describes an instrument which, in effect, de- termines the sulfur as the emission signal from a flame photometer. This system has a number of advantages in that it is pretty direct and needs a minimum of sample preparation and that it gives good readable signals. This is very valuable for all ball park data and for conditions which are highly controlled and highly reproducible so that the data can be interpreted quite accurately into sulfur concentrations.

* Kittelson D. B., McKenzie R., Vermeersch M., Dorman F., Pui D., Linne M., Liu B. and Whitby K. (1978) Atmos- pheric Environment 12, 105-l 11.

One of the major problems of the determination of sulfur is the number of chemical forms in which sulfur exists in the atmosphere. In particularly, ammonium sulfate, sulfuric acid and sulfur dioxide, are common forms of sulfur and it is very difficult to distinguish these in practice.

This instrument is no exception and gives significantly different responses to these different compounds. The authors are to be complemented in their thorough investigation of this chemical interference and for their documentation of the data which they obtained.

Based on their information, it should be possible to set up a monitoring system, providing the sample does not fluctuate greatly in composition. Of course, this would not be possible in the case of a number of air pollution samples, but must be the case in many plant effluents.

This instrument is a valuable contribution and will surely find application in industrial control labs.

Lmisiana State University, Baton Rouge, Louisiana, U.S.A.

J. W. ROBINSON

DRY DEPOSITION OF SO; metres of the atmosphere (e.g. Shepherd, 1974; Whelpdale and Shaw, 1974). In addition to this it is an important

Platt’s paper presents SO2 concentration profiles over an contribution because it is a semi-continuous study, where altitude range that is intermediate between the flights of previous work has usually been conducted over limited Georgii (1970) and the measurements made in the first few periods. A point to which the author does not attract

attention is the fact that of the hundred or so profiles

* Platt V. (1978) Atmospheric Environment 12, 363-367. represented in Fig. 4,30% have SO, concentration gradients that decrease with height. While one is at a loss to explain the