662 Discussions

is damped which would indicate some kind of saturation tion is not to be considered as a result, per se, but should process or inertia to changes. There should be a theoretical be a starting point for further research. explanation to the results stated here very superficially and only qualitatively In conclusion: The statistical analysis should be deepened and be used as a starting point for Department oj Mathematict S. TAURER a more theoretical investigation of the phenomenon which Portland State Uniuersit> will probably lead to physically interesting results. More Portland generally, an empirical application of a statistical distribu- Oregon 0737

LOCAL DISTRIBUTION OF CHLORINATED HYDROCARBONS

In the paper. “Local Distribution of Chlorinated Hydro- carbons in the Ambient Air in Tokyo” by T. Ohta, M. Morita and 1. Mizoguchi, the authors have significantly expanded our information on some of the characteristics of these important compounds in urban situations.

However, in the matter of chlorocarbon concentration correlations with weather the authors fail to mention poss- ible interactions of weather factors. One relationship that might be logical is for rainy days to be windier than aver- age. Thus, the lower concentration on rainy days as noted in the paper could be due to a rain-wind speed correlation. This might be easier to explain than the solubility-washout mechanism mentioned by the authors. The lack of an in- verse correlation between wind speed and concentration, as is frequently found in diffusion work, may also be due to a wind speed-wind direction correlation. The authors might wish to comment on the typical correlations to be expected between weather elements in the Tokyo area.

With regard to the way the wind data were obtained for the indicated correlations as I understand the text, the

wind observations were not coincident wtth the sample collection. This could introduce additional variations into the analysis especially in those periods of the study when a significant diurnal cycle in the wind occurred.

The fact that the CCIS ratio of air concentration to pro- duction is greatly different from the other compound ratios is puzzling. Could it be indicative of a natural source of Ccl,? Perhaps there is some error in the Ccl, data since the Tokyo value is about 7 times that quoted for Los Angeles. (Not really “almost the same” as mentioned by the authors.) If the Ccl, data were found to be closer to the Los Angeles value then a correction for a geophysi- cal background of about 125 ppt might bring the ratio closer to the other values. We have found Ccl, concen- trations averaging about a value of 125 ppt in a large number of remote samples in the western USA.

Useful, good research seems to always answer some questions and to raise new ones. This study fits this pat- tern.

Air Pollution Resrurch Chemical Engineering Washington State University Pullman, Wash. 99163. U.S.A.

ELMER R~HINSON

“IMPROVED THIN-FILM SULPHATE TEST FOR SUBMICRON PARTICLES”

Dr. Ayers is to be congratulated on the beautiful results of his experiments. I think it is astonishing that he expresses surprise that bisulfate yields a positive test, but not that sulfuric acid does the same. I strongly suspect that. at 959: relative humidity, the key question is the deli- quescence of the collected salt particle rather than its solu- bility per se. This would certainly explain the failure of calcium sulfate to react.

1 am continually appalled at the amount of effort pre- sently devoted to the reinvention of the wheel. The particu- lar sequence of vacuum evaporated reagents is new, and, as noted above, the author deserves credit for finding them. However, practically every other aspect of the entire work has been done previously, yet the bibliography is extremely sparse. It would not seriously detract from the present work to note the previous studies that are confirmed by the present work.

Consultant in Atmospheric Chemistry JAMES P. LODGE, JR. 385 Broadway Boulder, Colo. 80303, U.S.A.

AUTHOR’S REPLY

Although Dr. Lodge is “appalled at the amount of effort devoted to the re-invention of the wheel” he must admit that the elliptical wheel I describe is a distinct improve- ment on the square or rectangular ones that he and others developed. The difference between this and earlier methods lies in the vapour deposition of reagents, which does not disturb the original particle, allows simultaneous sizing and analysis for a given constituent and, in this case, is capable of detecting amounts of sulphate down to about lo~-r’ g.

Dr. Lodge’s comment regarding the positive test results Division of’ Cloud Phy.sics

for bisulphate and sulphuric acid is. of course, quite cor- CURD. Sydney

rect, With regard to his second comment it should be Australia

remembered that the collecting surface and the particles are covered by a thin layer of barium chloride which is itself deliquescent, so that above 90:;, relative humidity it forms an aqueous solution over the surface. Thus the par- ticles being tested are in contact with an aqueous layer and solubility, rather than deliquescence, should determine the ability of the particles to react. For the KzSOl particles to have reacted at all at 95”, r.h. when the vapour pressure over saturated K,SO, solution corresponds to >97:;, r.h. indicates that some dissolution of the particles into the aqueous layer must have occurred. It is true that at loo”,, r.h. K2S0, reacts more typically than at 95:,, r.h.; how- ever. CaSO, would not react even after IO days at !OO”, r.h., and even though there was evidence that an aqueous solution of barium chloride had formed over the surface. Whilst puzzling perhaps, these observations still seem bet- ter interpreted in terms of solubility, since in all cases at 95”;, r.h. and above the particles are in contact with an aqueous layer.

G. P. AYERS