mena associated with cloud are likely to become increasingly incorporated in the data sets. Precipitation was found to have important in higher latitude maritime situations, have the little influence on those components most highly correlated authors any suggestions for incorporating this factor in their with sulfate. Further discussion of these results as well as PCA model? of seasonal stratified data will be reported in a later paper.

D. J. MCIORE We have applied PCA to the analysis of 3-h average sulfate

data collected for the Electric Power Research Institute’s Sulfate Regional Experiment (EPRI SURE). Both cloud cover and precipitation were included in our analysis. We found that those components highly correlated to sulfate did not depend strongly on cloud cover or precipitation. Also, those components highly correlated with cloud cover were almost never important in explaining sulfate. In particular, a component with a lack of clouds but with high ozone and SO,, was often most important in determining sulfate levels in the summer months.

AUTHORS’ REPLY

Dr. Moore’s comments and question on incorporating variables related to cloud processes in the Principal Com- ponent Analysis (PCA) are very well taken. Standard weather records often contain estimates of cloud cover, occurrence of fog, and precipitation. The exclusion of these variables certainly increases the ambiguity of interpreting our results with regard to the relative importance of water vapor vs water droplets in sulfate formation.

Cloud cover and fog statistics were not collected for our study because 24-h averages are required to be comparable with the 24-h average particulate sulfate data. As the 24-h particulate sampling period extended from 11 a.m. to 11 a.m. LST, this would have required special processing of the hourly data from the U.S. National Weather Service. Daily precipitation data for New York and Los Angeles were later

At this time we have had little success in finding a relationship of cloud cover and sulfate levels. Perhaps a parameter such as the number of hours of fog during the particulate sampling period would be more significant than cloud cover in determining the importance of water droplets in sulfate formation.

Environmental Research & Technology, Inc.,

2625 Townsgate Rd., Suite 360, Westlake Village, CA 91361, U.S.A.

RONALD HENRY G. M. HIDY

Discussions 271

THE EFFECT OF NITROGEN DIOXIDE AND OF SOME

TRANSITION METALS ON THE OXIDATION OF DILUTE BISULFITE SOLUTIONS*

The author presents the study ofreactions systems which are of great interest to atmospheric chemists. My concern stems from the fact that following the course of a reaction con- ductimetrically requires foreknowledge of the products of the reaction. In the NO,-sulfite system the author’s treatment of the data and internretations are limited to the formation of SO:-, NO;, NO; and H’. Sato et al. (1979) have reported that the reaction of NO2 with sulfite at 25°C in neutral to alkaline solutions produces SO:-, S,Oi-, NO;, HON(SO& and Hf. At 70°C HON(SO,)$- reacts with HSO; to produce N(SO& which hydrolyzes to HN(SO,)$ - and SO:-. Very little NO; was formed except in acidic solutions where NO; oxidized HON(SO,)t-. HN(SO,):- and N(SO& to SOi- and itself hydrolyzedto NO, NO, and NO;. Recent investigations by Markowitz (1979) also show similar patterns. While one may explain the formation of dithionates via the termination reaction of two SO; moieties, the formation of HON(SO,)s- and the lack of formation of NO; is hard to explain in terms of the mechanistic model proposed by the author. Admittedly the experiments cited above were conducted with substantially higher sulfite concentrations but the question remains as to what extent these species are formed in dilute solutions and this in turn is the determining factor for the validity of the mechanistic model proposed by the author.

In addition, I think it is worthwhile to reiterate that the lack of any observable effect due to manganese is disturbing, in view of the extensive amount of literature available on that system.

California Primate Research Center,

t,rniversity of California. Daois, CA 95616, U.S.A.

PURNENDU K. DASGUPTA

*Nash T. (1979) Atmospheric Environment 13, 1149-l 154.

AE 14:2--H

REFERENCES

Markowitz S. (1979) Department of Chemistry, University of California, Berkeley, CA 94720. Personal communication.

Sato T., Matani S. and Okabe T. (1979) The oxidation of sodium sulfite with nitrogen dioxide. Paper No. INDE 210. ACS/CSJ Chemical Congress, Honolulu, Hawaii. l-6 April 1979.

AUTHOR’S REPLY

The new evidence (not available at the time) mentioned by Dr. Dasgupta certainly raises some queries regarding the reactions involved. I was working with very dilute solutions and minimal doses of nitrogen dioxide, so perhaps some of the species he describes were not so important in my case, particularly “hydroxylaminodisulfonate” which looks as though it would be the result of a termolecular reaction. There can still be no question regarding the catalytic activity of nitrogen dioxide, and the continued rise in conductivity after absorption of the gas is still best interpreted on the Backstrom chain hypothesis.

With regard to the lack of catalytic effect of manganese, I suggest that the reason was the same as for copper (some effect, but very small compared to that of iron) i.e. the low working pH, around 4.6. Ferric iron would still be massively hydrolysed, copper only slightly and manganese, presumably, not at all. Fuller and Crist (1941) worked at pH 8.7 with copper, at which considerable hydrolysis might be expected, and stated (twice) that “oxidation of sulphite was due to some primary process not involving cupric ion”. The same reason- ing could apply in the case of the other two metals.

Chemical Defense Establishment, Porton Down,

T. NASH

Salisbury, Wilts SP4 OJQ. England

REFERENCE

Fuller E. C. and Crist R. H. (1941) The rate of oxidation of sulfite ions by oxygen. J. Am. C&m. Sot. 63, 16441650.