JOURNAL OF
THE CLEAN AIR SOCIETY OF
AUSTRALIA AND NEW ZEALAND
Vol. 17. No. 3, August 1983
President: K. M. Sullivan Secretary: R. W. Manuell Treasurer: Dr. K. S. Basden
Postal Address:
Box 191. Eastwood. N.S.W. 2122. EDITORIAL
J. D. Court 34
BRANCH PRESIDENTS ACT: Dr. N. J. Daly NSW: J. D. Court NZ: J. Hickman Qld: J. S. McFarlane SA: E. F. Symons
Vic/Tas: Dr. J. B. Robinson WA: D. G. Saunders
BRANCH CORRESPONDENTS ACT:
NSW: Steve Stanley NZ: Ron Pilgrim Qld:
SA:
Vic/Tas: Jack Chiodo WA: D. B. Sykes
TECHNICAL PAPERS
Aluminium Anodising: Control of Fume Emissions from Ancillary Bright Dip Operations
H. M. Evans
Latrobe Valley Pollution Characteristics R. C. Joynt
Some Meteorological and Source Characteristics of High Hourly Pollution Events in the
Latrobe Valley R. D. Hoy
39 42
50 SPECIAL REPORT
Highlights of the 6th lUAPPA Congress. Paris, May 1983.
R. W. Manuell 36 FEATURES
Announcements 34, 35, 48
Book Reviews Company News
Conferences and Courses lUAPPA News
Overseas News
35, 37 37 55 34 35
The opinions expressed by authors and contributors are their own and do not necessarily represent the view of the Society.
EDITOR Dr. R. G. Gillis,
75 Downshire Ro.. Elsternwick.
Victoria 3185, Australia.
Phone: (03) 528 2507.
ASSOCIATE EDITOR Sylvia J. Mainwaring EDITORIAL BOARD R. G. Gillis
H. F. Hartmann Sylvia J. Mainwaring J. O'Heare
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CLEAN AIR is listed in Current Contents
EDITORIAL
It is appropriate from time to time to reconsider our goals and our progress in achieving them. In its principal aim, the abatement of air pollution, our Society is aligned with the wider community which holds ciean air as one of its principal environmental aspirations. Indeed we would expect the views and opinions expressed in the Society to mirror, on a more sophisticated level, those generally held in the community.
While this basic aim has not changed since the Society was formed in 1967, the emphases and priorities have shifted considerably. As one in the public "firing line", I can testify that community expectations for clean air have been steadily rising. The smoking chimneys and gritty fallout may have largely disappeared, but public concern has now shifted to more subtle forms of air pollution such as lead, photochemical smog and respirable particulates. However, there has been another notable shift. No longer is the control of air pollution regarded as an
"absolute good" to be pursued at all costs. Consequently there has been a marked diminution in the rate of growth of resources committed to the task of air pollution control in the private, public and academic sectors.
How have we coped with this change in emphases and circumstances? How' are we set to cope in the future?
We are faced with a situation where our best scientific and engineering efforts have failed to resolve quantitatively the fundamental questions of the costs and benefits of air pollution control. We have instead left it to parliamentary processes and economic forces to sort out the conflicting interests in air pollution matters, with little attention as professionals to the working of those processes and forces.
You might question that the case is really so uncertain. Let me put two scenarios to you. Firstly, in our own situation we have adopted the essentially British approach of "best practicable means" for nearly two decades. In following this course we
have not satisfied public aspirations for clean air and our decision makers still face the same basic uncertainties as they did when we first started. Brian Robinson in his editorial in May 1981 suggests one tool for improving our performance would be better
"predictive modelling". While I concur, I also point out that the fundamental conflicts, which need to be resolved by subjective judgements, will still remain even after the future air quality has been accurately predicted by modelling. The second scenario is represented by the US approach to air quality management.
Ken Basden, in his February 1983 editorial, has highlighted the enormous complexity of the American approach and the very considerable commitment of resources needed to make it workable. While endorsing Ken's call for greater training in this country, we must realise that, we can just never expect to have resources on this scale in Australia. The real fact is that our resources are probably slightly less now than they were some five years ago.
The American approach will not solve our problem.
When I consider the membership of the Society, it is apparent that although a broad range of community opinion is represented we are predominantly
"technical". By training we are mostly chemists or engineers, with the occasional meteorologist of physicist among our ranks. By role we tend to be industrial engineers and managers, consultants, government officials or scientific academics and researchers. In the interpretation of our requirement for ordinary membership, namely,
"engaged in or having a genuine working interest in the principles and practice of air pollution control", we have eschewed direct political involvement or direct involvement in what might be called conservationist lobby groups.
Now, while I believe this has been a basically sound judgement, I suspect it may have cut us off from a consideration of the genuinely subjective elements which are part of the community's perception of air pollution. Admittedly, in recent years, we have seen more papers on the social and economic aspects of air pollution control at our conferences, symposia and regular meetings. But by and large, we do not find social scientists, political scientists or economists among our ranks.
How then, as a specialist Society, can we contribute to the broader community debate on the resolution of air quality issues. I would not suggest that we enter the political or lobbying domain directly. However, I think we could give more attention to the real political, social and economic forces which contribute to the community
"decisions". One aspect which arouses my interest is the possibility of using economic tools such as charges and taxes, in contrast to legislative restrictions, to achieve community air quality goals. There is a real risk that our present techniques for administration and control may collapse under their own weight in the not too distant future unless we consider some alternatuves. However, these are speculations, and they could hopefully be put into some perspective by review of what we have done and achieved from a historical and political viewpoint. Perhaps we should ask a few historians and political scientists to contribute to our discussions on occasion.
JOHN COURT,
President, New South Wales Branch.
IUAPPA NEWS
Ken Sullivan President
At the executive meeting during the Paris Congress the following officers were elected for the next three years:
President, Ken Sullivan (Aust), First Vice-president, Dick Manuell (Aust), Second Vice-president, Dr. L. A.
Clarenburg, (SICOM, Holland); Dr.
Michel Sommer, Immediate Past President; Rear-Admiral P.G. Sharp, Director-General. The executive also has representatives from France, Federal Republic of Germany, Italy, Japan, South Africa, United Kingdom, the United States of America and Canada.
ANNOUNCEMENTS
Discount on Books for Members Books published by Butterworths (which includes the Ann Arbor Science label) advertised in the Journal, are now available at a discount of 15 per cent to members of the Society and Journal subscribers.
Details of the publication/s required together with a cheque or money order made payable to the Clean Air Society of Australia and New Zealand should be sent to the Circulation Manager, P.O. Box 191, Eastwood, NSW, 2122, Australia. Publications will be forwarded direct by mail from Butterworths.
It is hoped that members will take full advantage of this new service.
ANNOUNCEMENTS
Listing of Air Pollution Control Consultants
Those members wishing to utilise this service are asked to read the following notice which will appear in every issue of Clean Air containing the Listing.
"The following listed consultants, all of whom are members of the Clean Air Society of Australia and New Zealand, have advised they are available for consultation services in one or more aspects of air pollution control. The Society provides this listing as an information service. It accepts no responsibility for the performance of the consultants listed, nor does it make any representation concerning their competence."
The first list will be published in the November 1983 issue. Consultants who wish to be listed are asked to complete the following questionnaire and return it to the Societv's Secretary, P.O. Box 191, Eastwood" NSW, 2122.
Name of Member:
Qualifications:
Name of Consultancy:
Address (es):
Phone (s):
Special Interests or Expertise (Please indicate)
Air Pollution, general I Analytical Services 2 Dust control 3 Vehicular emission control 4
Industrial emission control 5
Health studies 6 Meteorological studies 7
Modelling 8 Stack monitoring 9 Ventilation 10 Other (specify) 11
OVERSEAS NEWS
New Clean Air Group Established in Singapore
Thanks to the generosity of the Singapore Convention Bureau and Qantas, the Secretary, Dick Manuell, was able to visit Singapore in March and speak at the inaugural seminar of the newly established Clean Air Section of the Singapore Society of Environmental Engineers.
Our Society had been encouraging the formation of a kindred group in the ASEAN area for some time and at the seminar the links were stengthened.
Speakers included Professor K. K.
Chin, President of the SSEE, Mr.
Martin Lee, Chairman of the Clean Air Section, and Mr. Lim Hung Siang, Higher Executive Engineer of the Singapore Anti-Pollution Unit.
Professor Chin spoke on broad environmental issues and the need for co-operative action between all sections of the community and welcomed the initiative of those responsible for establishment of the Clean Air Section within the umbrella of the SSEE. Mr. Martin Lee, Environmental Co-ordinator with a major oil company, endorsed the Professor's remarks and indicated the objectives of the Clean Air Section were based on respect for the environment and a desire to help Singapore improve its air quality. Mr.
Lim traced the history of the Anti- Pollution Unit from its inception in 1971 to the present day when it operated 14 monitoring stations covering 7 pollutants, providing a network over the whole island.
Significant reductions in smoke and NOx had been achieved, but dust fallout and suspended particles were still high, probably due to the intense construction activity occurring throughout Singapore. With 174,000 cars and 4,000 factories, it was not.
surprising that ozone levels exceeded 12pphm on occasions (approximately 20 days average in 1981). The Anti- Pollution Unit was happy to discuss problems with industry and advise on acceptable solutions and was pleased to see the initiation of the Clean Air Section.
Dick Manuell recounted the situation leading to the establishment of the Clean Air Society of Australia and New Zealand and emphasised how support from industry, academia and government enabled it to provide an objective, unbiased forum for resolution of air pollution control problems. He recommended this model to the Clean Air Section. In a second paper he illustrated how the Society had assisted the control of hydrocarbon emissions in the Sydney- region to be implemented in a cost- effective manner by the oil industry- through a scries of seminars and meetings which helped generate a better understanding of the problem of smog generation, and adoption of a reasonable timetable for introduction of controls, which has assisted in minimising their cost to the community.
Close co-operation between the new- Clean Air Section and Clean Air Society of Australia and New Zealand is envisaged. Clean Air Society of Australia and New Zealand has offered to sponsor Clean Air Section for observer membership of IUAPPA and to provide speakers from time to time. Branches are asked to keep this in mind and to advise the Secretary if any branch members are available to address the Clean Air Section on air pollution control.
BOOK REVIEWS
Air Pollution Control Equipment. H.
Brauer and Y. B. G. Varma. Sprlnger- Verlag, 1981. 388 pp.
Mv initial reactions on reading the first chapter of this book were decidedly negative, both the phrascologv and the grammar in this chapter are more than a little odd in places and bear unmistakable marks of having been translated, seemingly in some haste, from a German original. Phrases such as "the chimney, of household fire stations" or "loose their identy should have been amended well before this book went to press. Of more concern, however, is the number of small yet annoying errors: for example, Table I has carbon monoxide, instead of carbon dioxide, as the fourth most abundant constituent of the air, and in Table 2 the sum of the given percentage distributions of SO:
between natural and anthropogenic sources comes to 110 percent instead of 100.
In contrast to my reactions to chapter one, however, mv reactions to the rest of this book were generally highly favourable. The main goal of the authors is staled to be the "presentation of knowledge on design and operation of equipment applicable to the abatement of harmful emissions into air" and in this they succeed admirably. The meat of the book is in nine major chapters on the design and operation of cyclones; wet dust scrubbers; fabric filters;
electrical precipitators; mist separators;
absorption equipment; adsorption equipment;
equipment for biological waste gas treatment;
and equipment for chemical waste gas treatment.
The structure of each chapter is similar: an introductory' section; some examples of industrial applications of the type or types of equipment concerned; a review of the characteristics and fundamentals of the processes used in the equipment; an analysis of design procedures and fairly detailed design approach; and finally the nomenclature and references. The theoretical and practical sides of process characteristics and fundamentals are well-handled, with the important and relevant equations being treated comprehensively, hull treatment of minor or peripheral aspects is not attempted; instead references are provided to more specialized texts and articles. The references are predominantly in German, which has both advantages and disadvantages. The depth and strength of the German literature on many aspects of chemical and environmental engineering is often overlooked by English-speaking scientists and engineers, and this book therefore provides a valuable entry ro the German literature in the field of air pollution control equipment. On the other hand, not everyone is fluent in German and to include more references to English language publications would have been helpful.
Among the authors' subsidiary aims in writing this book was to produce a volume which besides presenting information on air pollution control equipment would also be useful as a textbook for engineering courses on environmental protection. The structure of the book is well suited to use as a text, as is the strict adherence to SI units throughout. In addition the large number of illustrations and the care taken to explain clearly exactly what takes place in different types of equipment enhances its usefulness as a text. The chapter on cyclones I found particularly informative, especially the section devoted to discussion of computer programmes for cyclone design.
One minor criticism I have is that the subject of particle size distribution is inadequately covered, a rather surprising fact in view of the important contributions made by German workers in the field of particle "and fluid dynamics. However, overall I feel that this book has a great deal to offer and I can recommend it to all those, in industry or the classroom, who are concerned with the detailed design and specification of equipment for controlling air pollution.
M. A. CONNOR.
Clean Air/August, 1983 35
HIGHLIGHTS OF THE 6TH lUAPPA CONGRESS PARIS, MAY 1983
R. W. (Dick) Manuell
Hosted by the French Association for the Prevention of Atmospheric Pollution (Association pour la Prevention de la Pollution Atmospherique APPA).
I U A P P A ' S 6th World Congress was attended by some 1100 delegates from forty-five different countries. Three hundred papers were presented in ten different themes. (1) Physics, chemistrv and measurement of air pollutants; (2) Health effects; (3) Odours; (4) Effects on the living environment; (5) Effects on building materials; (6) Meteorology; (7) Preventive techniques, reliability of installations and economic evaluation;
(8) Radioactivity; (9) Vehicular pollution; (10) Pollution caused by replacement energies.
In addition to the oral papers there was a very large poster section. Pre- prints of all but a very few of the papers were available at the opening of the Conference, bound in six volumes.
As the two official languages of lUAPPA are English and French, all papers were delivered in either of these languages and simultaneous translation services were provided for those needing them. With three and even four parallel sessions it was necessary for delegates to be very selective in the sessions they attended and it should be appreciated that, in the resume following, the observations represented a mixture of personal attendance and post-conference reading of the papers not heard.
Theme One: The Physics, Chemistry and Measurement of pollutants
The principal pollutants discussed included oxides of nitrogen, photochemical pollutants, acid rain, particulates, polycyclic aromatic hydrocarbons and hydrogen fluoride.
Mr. Graham Johnson's paper, "An empirical Model of Photochemical Smog Formation," which correlated smog precursors to Sydney smog more accurately than any previous model, received wide attention. Field measurement of oxides of nitrogen — a notoriously difficult exercise — was promised some relief by a paper by Messrs. Alan and Phil on a new portable analyser NOx using a galvanic cell. Several papers dealt with other forms of new analytical tools, including interferential spectrometry, pulse photolysis, resonance fluor- escence, Raman microspectroscopy, reflection X-ray fluorescence and a number of other techniques related to the measurement and size distribution of aerosol particles. Papers from members of the Clean Air Society of Australia and New Zealand in this section included those by G. M.
Johnson, K. M. Sullivan.
Theme T w o : Atmospheric Pollution and Health
This section included twenty-nine papers. There was a substantial increase in attention to indoor pollution with emphasis on the need to consider the impact of parental smoking on the health of young children, shown in an epidemiological paper by Dr. Waller of Great Britain, to have a significant effect on the incidence of chronic respiratory disease in young children. Other papers continued with this now classical triad of microclimate, epidemiology and biology being brought together to identify and, hopefully to quantify the effects of specific pollutants. PAH's, other particulates, including those associated with the metals lead, cadmium and vanadium, carbon monoxide, NOx, aerosols, unburned diesel fuel vapours, components of automobile exhaust emissions, all received close attention through animal studies, determination of mutagenic activity and more careful measurement than lias been previously reported.
Theme Three: Nuisance Odours The highly personal and subjective issue of nuisance odours causes a lot of controversy for pollution control authorities as well as those who generate the odours and those who have to suffer them. Papers by Brose, Bahmuller and Behringer, all of the Republic of Germany, gave new hope for really quantitative assessment of odour intensity, while papers from Moriguchi and others from Japan and Martin of France, gave promise of better odour control.
Theme Four: Atmospheric Pollution and Plants
The use of lichens and other plants as monitors or sentinels for the detection of air pollutants continues to provide a useful and economic system. Sulphur dioxide, peroxyacetyl nitrate (PAN), and fluoride ion have all been monitored using this approach. The subject of acid rain was discussed, leading one to the conclusion that this phenomenon calls for some form of global monitoring.
Theme Five: Atmospheric Pollution and materials
This section continued the theme of building damage related closely to the incidence of acid rain and highlighted the need to control the insidious effects of air pollutants on the fabric of many ancient and venerable buildings of Europe.
Theme Six: Meteorology and Atmospheric Physics
The first paper in this section by Mr.
R. Hyde of Australia, concerned a meteorological study of the Hunter Valley and indicated the very significant role meteorology can play in the proper environmental assessment of the development of new industrial regions and also of the need to carry out specific field studies.
Papers by Cariolle and Royer, both of France, continued in this disciplined approach by demonstrating advances in the modelling of increasingly- important topics such as carbon dioxide levels and stratospheric ozone perturbation. Proper attention to meteorological factors has definitely improved the accuracy of modelling of pollutant behaviour in the atmosphere.
Theme Seven: Preventive Techniques — the reliability and safety of installations — economic evaluation
This section included several excellent case studies of successful control techniques for a variety of pollutants.
Pollutants covered included, phenols, zinc, ammonia, mercury, lead, aldehydes, amines and hydrocarbons.
Fugitive emissions, hazardous waste incineration, plume rise and thermal radiation also received some novel attention. There were two papers by members of CASANZ in this section, including one on "Evaluation of the Causes of Difficult Collection of Coal Flyash in Electrostatic Precipitators,"
by Cross and Poulson and a "Case History on the Use of Fabric Filters for Cleaning Flue Gases from ten 660MW Coal Fired Power Boilers in New South Wales" by Lam and Rigden.
Theme Eight: Control of Radioactivity
In this rather small section, attention was paid to the emission of the radionuclides from coal-fired power plants and to comparisons of the emissions of coal and nuclear fuel cycles.
Theme Nine: Automotive Pollution
Modelling techniques for predicting the quantities of pollutants emitted by vehicular traffic are now highly advanced as the paper by Faugere and Franceries of France, indicated.
Considerable attention was given to PAH emissions and there were some five papers covering the toxicity of diesel motor emissions, but the conclusions were by no means unanimous. There was a strong emphasis on health effects in this section of the Congress and it is evident that more attention will need to be given to particulate matter in the future.
Theme Ten: Pollution caused by Replacement Energies
This section really followed the increasing use of coal for power generation and the need to control NOx and flyash more effectively.
Between eight and fifteen percent of the unit cost of generating power at present is required for the control of flyash and the use of fluidised beds is being studied with a view of reducing flyash generation and therefore this considerable pollution control cost (In a paper by Dutkiewicz and Petrie, South Africa). Two papers discussed the problems associated with the use of wood fuel and one from Rolfe of New Zealand, a member of CASANZ, discussed air pollution associated with geothermal energy.
Even from this brief look at but a few papers of the three hundred, it is
evident that a great deal of information leading to the better control of air pollution was made available through this remarkable Congress and it is hoped that the papers will be given wide dissemination, particularly among those countries who are only now considering the need to control air pollution for they should be in a position to avoid some of the mistakes made in the countries where air pollution control has evolved through a long process before reaching its present advanced status.
Mr. de Rosen, representing the United Nations Environment Protection Agency from Nairobi, in his closing speech to the Congress drew attention to three matters relating to air quality, namely: (1) Acid rain; (2) Disruption of the ozone layer; (3) The level of carbon dioxide in the atmosphere. He mentioned that UNEP was very interested in these three topics and was considering the establishment of a Coordination Committee to provide some international integration of efforts to properly analyze these three phenomena. It is hoped that IUAPPA and its members will be able to assist in these matters. Mr de Rosen also expressed the hope that IUAPPA would extend its geographical scope to include many more countries in the future and IUAPPA is currently considering how it can assist in this level of awareness about atmospheric pollution problems and their control.
COMPANY NEWS
Beckman to Build Emissions Monitoring System for Ford Beckman Instruments (Australia) Pty.
Ltd. are pleased to announce the award of a major contract from the Ford Motor Company of Australia Ltd. The contract is for the design and supply of automotive emission monitoring equipment for Ford's extensive emissions laboratories at their Proving Ground in the You Yangs, Victoria. It is believed to be the largest system of its kind to be built in Australia.
The total system, which includes three analyser benches, a master control unit and sophisticated sample handling and conditioning equipment, will be designed and built at Beckman Instruments (Australia) Pty. Ltd.
Process Instruments and Controls Group's head office and factory in Mount Waverley, Victoria. When completed later this year, the systems will be staged at the factory for customer acceptance trials prior to being shipped to Ford's laboratory where it will be linked to their computer via Beckman customer built computer interface.
BOOK REVIEWS
Health Effects of Fossil Fuel Burning.
R. Wilson, S. D. Colomi, J. D. Spongier, D.
G. Wilson. Bollinger Publishing Co., Cambridge, Mass. 392 pp.
The authors associations with Harvard Universitv (two of them with the prestigious School of Public Health) and Massachusetts Institute of Technology alone ensure the importance of this book. The authors purpose is to determine which of the many emitted pollutants cause adverse health effects and tO assess those effects. Although the information on this topic is voluminous, it is imprecise and inadequate and, largely, will always remain so.
As emitted pollutants are set to increase year bv vear with a return to the use of coal, assessment of possible health hazards associated with those emissions is of paramount importance. While emissions arc increasing, atmospheric concentrations have been generally reduced, though they have been spread over a wider area. This leaves a dilemma: if adverse health effects arc still present at lower pollutant levels, thousands of people would be affected;
yet if these effects do not exist, or if we control the wrong pollutants, we would be doing so at fantastic expense.
The evidence on health effects whether laboratory tests or epidemiological studies is carefully reviewed. The evidence appears to be inconclusive with one group of researchers stating that the data arc consistent with an air pollution-related effect while the other group says that, an air pollution-related effect cannot be 'proved. The problem is that experiments arc- not sensitive enough to give us decisive answers to the questions legitimately asked. However, the authors incline to the opinion that small particulate matter, essentially sulphate is likely to be associated with chronic respiratory disease while the effect of low concentrations of sulphur dioxide and nitrogen dioxide appears to be ephemeral. Further improved studies are deemed essential.
One chapter is devoted to control measures.
In the final chapters the concept of cost-benefit studies is explored and the authors believe that the difficulties are not insuparable and show how- such studies can be undertaken.
As evidence is mounting that no threshold exists for some pollutants such as carcinogens and some others, low pollution levels are advocated. But it is stressed that the concept of threshold should not disappear for legislative purposes. To achieve zero discharge at all times and at all places may be virtually impossible.
Increasingly sensitive instruments will become available with which inspectors will be able to demonstrate that some discharges, even if they are infinitesimal, will have occurred. If the legislation does not prescribe a threshold, the inspectors or the courts will do so or otherwise there would have to be a wasteful expenditure in prosecuting, defending, and trving inumerablc rather trivial cases. There is also little point in devoting society's resources to reducing to zero the exposure to one type of pollutant where there may be a natural background level that is relatively high and quite unaffected by such measures.
Pollution pricing and emission charges as well as their legal implications conclude this thought- provoking book.
H. F. HARTMANN
Clean Air/August, 1983 37
ALUMINIUM ANODISING:
CONTROL OF FUME EMISSIONS FROM ANCILLARY BRIGHT DIP OPERATIONS
Hugh M. Evans
Hugh Evans is an Air Quality Officer with the Environment Protection Authority of Victoria, 240 Victoria Parade, East Melbourne, Vic. 3002
ABSTRACT. Bright dipping, the process of chemically polishing aluminium components prior to anodising, requires immersion in a heated nitric acid phosphoric acid based liquor which in turn generates an acidic misty brown fume. This fume should be completely captured and effectively treated before being discharged to atmosphere, otherwise there is "acid fallout" causing personal injury (acid facial burns) and property damage (usually damaged motor car body paintwork). There had been apparently no completely effective means for cleaning such fume anywhere in the world.
The Environment Protection Authority of Victoria (the EPA), the statutory authority in the Australian State of Victoria responsible for air pollution control, tackled this problem. It called upon the Australasian Institute of Metal Finishing (AIMF), the anodisers in question and other commercially interested parties such as chemical suppliers and pollution control equipment suppliers for assistance.
A working party was formed and carried out a scries of pilot scale fume scrubbing trials on commercially produced bright dip fume at the works of one of the anodisers.
The working party found:
(i) bright dip fume to be air contaminated with nitrogen oxides, mostly nitrogen dioxide (250-500 ppm) plus an unknown level of nitric acid, as both vapour and mist;
(ii) nitrogen oxides do not cause acid fallout and can therefore be disposed of by dispersion from a stack of adequate height;
(iii) nitric acid had to be eliminated, or substantially reduced before final discharge. Water scrubbing on its own was not adequate, because of the entrained fine nitric acid mist. Mist elimination, on its own, was unsatisfactory because of the nitric acid volatility;
(iv) the most effective means for cleaning this fume appears to be water scrubbing followed by mist elimination.
The EPA will recommend to the Victorian Government that these findings be incorporated into Schedule F (minimum control requirements) of the State Environment Protection Policy — The Air Environment.
Further work is necessary to determine the levels of free nitric acid encountered during the various stages of fume treatment, the effect of siting the ancillary exhaust fan before or after the scrubber, and also the effect of dosing the fume with gaseous ammonia before treatment.
THE ANODISING PROCESS.
Aluminium components are anodised to give an attractive protective aluminium oxide surface film which may be silvery or coloured and which may either be dull or brightly polished.
In Victoria there are 17 anodisers, all located in the Melbourne metropolitan area. Eleven of these have facilities for producing brightly polished anodised components, of which five works can handle large components, i.e. having a length of 3m or longer.
When a brightly polished surface is required, the aluminium component is given a preliminary treatment prior to anodising, by either electropolishing or chemical polishing (bright dipping). In Victoria, in common with USA, UK and much of Europe, chemical polishing is the commercial practice.
In the case of electropolishing, the brightly polished surface is achieved by passing a high density electric current through an alkaline aqueous solution onto the surface of the component being treated, making sure that the current density is uniform over its entire surface. Therefore extreme care has to be taken in placing the components on the rack to ensure good electrical contact and hence a
uniformly polished surface. Electro- polishing generates an alkaline spray which can be readily cleaned.
Chemical polishing requires less capital and gives a uniformly polished surface with very little effort. In this case the components are attached to a suitable jig which is then dipped, drained and rinsed. Contact between the component and the jig is not critical.
The liquor (polishing agent), which is maintained at 100-115°C invariably contains orthophosphoric acid (H3PO4) and nitric acid (HNO3), a typical composition being 80 percent H3PO4, 15 percent H2SO4, 5 percent HNO3 plus a specified trace amount of dissolved copper.
This operation gives off an acidic misty brown fume which has to be completely captured and effectively treated before finally discharging to the atmosphere. If this is not completely done acid fallout occurs causing both personal injury (e.g., acid facial burns) and properly damage (e.g., damaged motor car body paintwork).
There had been apparently no completely adequate means for controlling such fume emissions anywhere in the world. Various forms of air pollution control equipment had been tried. Irrigated baffle plates and water sprays did not appear to have any effect. Water irrigated packed tower type scrubbers appeared to show some partial cleanup.
In May 1979, such matters were brought to a head when several employees of a works adjacent to an anodiser who bright dips encountered substantial damage to the paintwork of their motor cars. They complained to the Environment Protection Authority of Victoria (the EPA), the statutory authority in the Australian State of Victoria responsible for managing air quality in Victoria. A trade union, representing these employees, also referred their complaints to the
Clean Air/August. 1983 39
Minister responsible for the EPA and also the Victorian Ombudsman. At the time the EPA, though it was well aware of this acid fallout problem, did not have a completely effective solution.
The EPA then called upon the Australasian Institute of Metal Finishing (AIMF), the anodiscrs in question and other commercially interested parties such as chemical suppliers and pollution control equipment suppliers, to assist in achieving an effective solution.
A WORKING PARTY was formed, comprising: Mr. L. H. Esmore representing the AIMF; Mr. H. M.
Evans and Mrs. A. Fisher — Air Quality Officers, EPA (Mrs. Fisher supervised the analytical work); Mr. C.
Allderidge of Silcraft Manufacturing Co. (a motor car component manufacturer with anodising facilities); Mr. B. Crews of Ceilcote Pty. Ltd. (a pollution control equipment supplier); Mr. R. Farhall of Aston Farhall Pty. Ltd. (a pollution control equipment supplier); Mr. I.
Jamieson of Albright and Wilson (Aust.) Ltd. (a chemical supplier).
This working party then set about this investigation by: (i) observing the behaviour of normal plantscale bright dip operations; (ii) observing the behaviour of nitrogen dioxide under various circumstances; (iii) carrying out pilot scale fume scrubbing experiments, and (iv) seeking technical advice from both local and overseas sources.
The pilot scale fume scrubbing experiments were carried out in the anodising section of the Silcraft Manufacturing Co. (a motor car component manufacturer) of Forster Road, Mount Waverley (a south- eastern Melbourne suburb). There was a steady supply of fume from Silcraft's bright dip facility.
The main fume exhaust duct was tapped and a 300 cfm sample of fume steadily drawn off and passed through the following equipment:
(i) two only 1' 10" dia. water irrigated counter-current packed tower type scrubbers, filled to a depth of 3' 0"
with 1" Tellerettes (provided by Ceilcote); (ii) one only Brink mist eliminator (provided by Aston Farhall); one only 300 cfm exhaust fan (provided by Albright and Wilson) and returned to the hooded space over the bright dip baths.
The following assemblies were used:
(i) one scrubber on its own; (ii) two scrubbers in series; (iii) the mist eliminator on its own; (iv) one scrubber followed by the mist eliminator, the fan being downstream in all cases. The nitrogen oxide level was measured before and after treatment.
The nitric acid level, whether as mist or vapour, was not measured quantitatively. The working party did not have a suitable method. Instead, the final exhaust was checked for acidity using pH paper.
FINDINGS. The working party found:
(i) the level of the oxides of nitrogen to be the same before and after passage through the scrubber (or scrubbers) regardless of the scrubber liquor pH, thus indicating negligible absorption of oxides of nitrogen. Nitrogen dioxide, the principal component, has a water solubility similar to that of carbon dioxide.
(ii) scrubbing removed the brown colour characteristic of nitrogen dioxide.
(iii) the scrubbers gave off an acidic (about pH 0) aqueous mist, even with alkaline scrubbing liquor.
(iv) the mist eliminator on its own gave a clear, but very acidic, discharge.
(v) when the mist eliminator was placed downstream of the scrubber the discharge was clear and not acidic in one case out of four, the nitrogen oxide level was unaltered.
ADDITIONAL FINDINGS. From other observations the working party also found:
(i) bright dip fume is free of both phosphoric acid mist and sulphuric acid mist. Silcraft uses lime treated water (its final liquid effluent) for irrigating the scrubber serving its bright dip facility. If entrained phosphoric acid mist were present in the bright dip fume, a calcium phosphate sludge would have formed in the used scrubbing liquor. As phosphoric acid is not present, sulphuric acid, the other non-volatile component of the bright dip liquor must also be absent.
(ii) the siting of the scrubber exhaust fan may affect the quality of the final discharge, with respect to the level of entrained acidic aqueous mist. Since 1976 Silcraft has operated a countercurrent water irrigated packed tower type scrubber with the ancillary fan sited before (upstream of) the scrubber without complaint and also without evidence of corrosion on its factory roof (located 10 metres east, being downwind, of the scrubber stack). Other bright dip anodisers with similar countercurrent packed tower type scrubbers, but with the fan being located after (downstream of) the scrubber, have encountered complaints. If located downstream of the scrubber the fan appears to substantially re-entrain any acidic aqueous mist. This aspect will be looked into further.
(iii) nitrogen dioxide, at 200-500 ppm, the concentrations encountered in bright dip fume is colourless at room
temperature (20-25°C). The reference gas, 850 ppm NO2 in nitrogen, supplied by Commonwealth Industrial Gases Ltd., the Australian associated company of the British Oxygen Company Ltd., is colourless at room temperature.
CONCLUSIONS. The working party then concluded that:
(i) chemical polish (bright dip) fume is an acidic misty brown fume consisting of air contaminated with about 250-500 ppm oxides of nitrogen, principally nitrogen dioxide, plus an unknown quantity of nitric acid, both as mist and vapour. There is no entrained sulphuric acid or phosphoric acid mist.
(ii) fume scrubbing does not lower the nitrogen oxide level. It does however remove the characteristic brown nitrogen dioxide colour, probably by cooling, so converting the brown NO2 monomer into the colourless N2O4 dimer.
(iii) the oxides of nitrogen as distinct from nitric acid (vapour or mist), do not cause acid fallout and can therefore be disposed of by discharge from a stack of such a height that the predicted maximum ground level concentration of nitrogen dioxide does not exceed the Policy objective of 0.15 parts per million (volume/volume) (refer Schedule B of the Victorian State Environment Protection Policy — The Air Environment).
(iv) the acid fallout is caused by the nitric acid whether as mist or vapour.
(v) the nitric acid mist droplets present in the bright dip fume are small, the estimated size being no greater than one or two microns. Such mist particles are too small to be effectively handled by counter-current water irrigated packed tower type scrubbers which at present are capable of handling mist droplets not smaller than 8 to 10 microns in size.
(vi) to date, such anhydrous nitric mist droplets cannot be effectively pretreated, i.e., coalesced to give a droplet size of 8 to 10 microns or larger, to enable handling in such a scrubber. On behalf of the working group the EPA has made worldwide enquiries without success.
(vii) mist elimination on its own, such as either a "Brink" type unit or an electrostatic precipitator, is not an effective means for controlling bright dip fume because of the volatility of the anhydrous nitric acid. Any collected nitric acid evaporates, giving a clear but extremely acidic discharge.
(viii) the most effective means for controlling bright dip fume is a two- stage unit comprising: (Figure 1) a counter-current irrigated packed tower type scrubber, continuously irrigated with an aqueous liquor maintained at a pH value of not less than 9.0;
followed by (2) a suitable mist eliminator such as either a "Brink"
type unit or a suitable electrostatic precipitator.
The purpose of the scrubber is to humidify the bright dip fume so as to convert the entrained anhydrous nitric acid mist to aqueous nitric acid mist thus substantially reducing the nitric acid volatility. The mildly alkaline scrubbing liquor is present to neutralise any nitric acid which may be absorbed by the scrubber, and also to provide a mildly alkaline mist, to co-exist with the acid mist, to act as a diluent for the latter when captured by the mist eliminator.
(ix) every measure should be taken to prevent re-entrainment of any settled mist. The exhaust fan should preferably be placed before the scrubber. The exhaust stack diameter should be sized to ensure that the mean stack velocity does not exceed 9 metres per second. If these precautions arc followed there may be no need for the ancillary mist eliminator.
FURTHER WORK. This investigation is not complete. It had been carried out with the prime purpose of establishing minimum control requirements for effectively controlling fume emissions from aluminium bright dipping. Such control requirements are presented in the appended code of practice. These are to be revised as further information becomes available.
Further investigation will have to be carried out into:-
(i) the measurement of nitric acid levels, as both vapour and mist, in the bright dip fume at the various stages of treatment. Such measurements were not possible at this stage because of the lack of a suitable analytical method.
(ii) the siting of the ancillary exhaust fan as to whether it should be placed before or after the scrubber, and
(iii) the effectiveness of gaseous ammonia injection into the fume prior to scrubbing so as to neutralise free nitric acid. In this case the ammonia and the nitric acid concentrations should be kept out of the explosive range.
ACKNOWLEDGEMENTS. The EPA publicly thanks each of the members of the working party for the co- operative manner with which they tackled this pressing problem and also for their contributions and the time and the effort they spent on the investigation.
Received for review, 17 June 1983; Accepted for publication, 9 July, 1983.
APPENDIX
Bright Dipping (Chemical Pol- ishing) of Aluminium Compo- nents Prior to Anodising: Fume Emission Control
Proposed Code of Practice (Minimum Control Requirements)
1. Buffer Distances
Recommended minimum distance from houses
(i) 300m — for bright dip oper- ators using dipping baths exceeding 500 litres in capacity (ii) 50m — for bright dip oper-
ators using dipping baths of 500 litres in capacity or less 2. Control Unit
The bright dip fume emission control unit shall comprise the following component items placed in the following order.
(i) fume collection hooding (ii) scrubbing unit
(iii) mist eliminator (if required) (iv) exhaust stack
plus a conveniently located exhaust fan
3. Corrosion Resistance
Each of the said component items shall be constructed from materials which ensure that any surface, exposed to fume generated from bright dipping, is capable of withstanding contin- uous exposure to such fume.
4. Details of Control Unit
4.1 The fume collection hooding serving any dipping bath and any ancillary rinse bath shall be designed to ensure complete capture of all fume generated from bright dipping.
4.2 The exhaust fan shall be sized to ensure complete capture of all fume generated bright dipping.
4.3 The captured fume shall then pass through a properly maintained scrubbing unit comprising of a tower
(i) packed with a suitable inert extended surface packing material in sufficient quantity to ensure a mean residence time of the gases undergoing treatment of not less than 0.55 second
(ii) irrigated with an adequate supply of a suitable liquor having a pH value of not less than 9.0, so distributed as to thoroughly and continuously wet all surfaces of the said inert extended surface packing material.
4.4 Means shall be provided to prevent the said exhaust fan from operating unless the pump supplying irrigating liquor to the said scrubbing unit is operating.
4.5 The exhaust from the said scrubbing unit shall, if necessary, be passed through a device which shall prevent anv acid fallout (Note 1).
4.6 The exhaust stack shall be sized to give a mean gas velocity of not greater than 9 metres per second (Note 2).
4.7 The exhaust stack shall be equipped with sampling points and means of access thereto both conforming with the Memoran- dum on Provision for Stack Emission Determinations publish- ed by the Environment Protection Authority.
4.8 The exhaust efflux (exit) velocity shall be not less than 15 metres per second (Note 3).
4.9 The exhaust stack shall terminate at a height (Note 4) such that (i) the predicted maximum
ground level concentration of nitrogen dioxide, as calculated by the method stipulated in Schedule E of this Policy, does not exceed the design value as given in Schedule B of this Policy, and also (ii) the predicted maximum
ground level concentration of nitric acid, as calculated by the method stipulated in Schedule E of this Policy, does not exceed the design value as given in Schedule C of this Policy.
5. The said bright dip fume emission control unit shall be properly maintained and operated.
Now 1. This requirement is not necessary for those existing installations where there has been no evidence of acid fallout that is, the absence of justifiable "acid fallout" complaints and also the definite absence of corrosion on nearby structures. For proposed installations this requirement may be temporarily waived providing that the proposed control unit in question has been designed with provision for the later installation of such a device and also that the proposed bright dipping anodiser agrees to install such a device should this be considered necessary, at a later date, by the Environment Protection Authority.
Note 2. This requirement is not necessary for installations fitted with a device to prevent acid fallout (refer clause 4.5). Its purpose is to prevent re-entrainment of liquor from the inside walls of the exhaust stack. It was inserted on the advice from the United Kingdom Alkali Inspectorate.
Note 3. This is achieved by coning the top of the stack at an angle not greater than seven (7) degrees to ensure from the vertical smooth flow.
Note 4. The exhaust stack should also be of sufficient length to ensure that the stack gas flow pattern across the stack gas sampling plane conforms with the Memorandum on Provision for Stack Emission Determinations published by the Environment Protection Authority.
Clean Air/August, 1983 41
LATROBE VALLEY
POLLUTION CHARACTERISTICS R. C. (Bob) Joynt
Bob Joynt works in the Research and Development Department of the State Electricity Commission of Victoria, Howard Street, Richmond, Victoria, 3121. He is a member of the Latrobe Valley Airshed Study's Interpretation Group.
ABSTRACT. Early results from an extensive air quality monitoring network in the Latrobe Valley, Victoria are presented. Measurements of the major indicators SO2, NOx, CO, O3 and local visual distance are summarised, together with an indication of their variation with wind speed and direction, time of day and season. Some discussion of the correlation of measurements at different monitoring stations and of the proportion of NO2 in ambient NOx is given.
INTRODUCTION. The Latrobe Valley, in eastern Victoria, is the site of large depostis of brown coal which form the basis for most of the State's electricity generation and for other industrial activities. There is considerable potential for increased utilisation of the brown coal resources.
The importance of air quality considerations in relation to industrial developments in the Latrobe Valley led to the initiation of the Latrobe Vallev Airshed Study (LVASS) in May 1977 (7). This is a continuing study carried out co-operatively by the State Electricity Commission (SEC), the Environment Protection Authority (EPA), the Latrobe Valley Water and Sewerage Board and the CSIRO Division of Atmospheric Research.
Air quality monitoring has been carried out in the Latrobe Valley for many years by the SEC and the EPA, but much more comprehensive data have been generated in recent years from the Latrobe Valley Air Monitoring Network (LVAMN) which operates under the auspices of the LVASS.
This paper presents some summaries, observations and analyses of available air quality data drawn from existing published and unpublished sources. The LVAMN is not fully into its operational phase at the time of writing and analysis of data is lagging behind production.
However, it is believed that the data available to date do provide a good indication of the main characteristics of air quality in the Latrobe Valley.
AVAILABLE AIR QUALITY MEASUREMENTS. The locations of air quality monitoring stations of the LVAMN are shown in Figure 1 in relation to topography, towns and industrial sources. A summary of results from operating stations for the year September 1980 to August 1981 is presented in Table 1 (2). Data are now available from the town stations at Moe and Traralgon; Morwell West and Morwell East are the only- township stations for which results are given in Table 1.
This table also allows evaluation of the results by comparison with the Air Quality Objectives established by the State Environment Protection Policy (3). Under these Objectives, Detrimental Levels are not to be exceeded, so the highest measurements during the period are to be compared with them. Acceptable Levels are not to be exceeded on more than three days in any year (one day per year for ozone one-hour averages) so the comparable measurement is the fourth highest daily maximum (second highest for ozone one-hour averages). If this measurement is greater than the Acceptable Level, the Air Quality Objective is not achieved at that location.
Visibility-reducing particulates are regulated by an Acceptable Level in terms of local visual distance (LVD).
The Acceptable Level is based on aesthetic considerations and measurements are made by light- scattering instruments. The fourth lowest daily minimum LVD is compared with the Acceptable Level.
Earlier data from the LVAMN have been published (1, 4) and present a similar situation to that shown in Table 1. Long-term trends cannot yet be determined from the LVAMN data.
Logged data are available from mid- 1979 from some stations; others did not commence until mid-1981.
Frequency distributions of SO2, NO2, NO, O3 and LVD have been published (4, Appendix I) and, with the exception of O3, they vary considerably from station to station.
This highlights the care needed in combining measurements from different stations to produce average figures for a region. The rural stations have been located to provide results representative of rural areas in the Latrobe Valley but the means of estimating a regional average remains to be determined.
Prior to the installation of the LVAMN, the SEC used a mobile van to monitor air quality in various areas of the Latrobe Valley at different times. This van, refurbished with a
Table 1: Latrobe Valley Air Monitoring Network. Summary of Air Quality Measurements for Year September 1980 to August 1981.
complete set of modern instruments, has been sited at the top of Mount Tassie, to the south of the Valley, since late 1981. Occasional evidence of plume indicators is noted but the effects are mostly very small (S02<
20 ppb, NOx < 40 ppb, 1-hour averages).
Two long-term surveys by the SEC have provided useful information on air quality in the Latrobe Valley. The indices are insoluble dust depostion and sulphation rate, as measured by- British Standard dust gauges and lead dioxide candles, respectively. The EPA also measures dust depostion in towns.
Results of these surveys and other pre- LVAMN measurements have also been published previously (4, 5). The LVASS Report on the present State of Knowledge concludes: "The information from these various studies . . . paints a broadly reassuring picture in relation to air quality in the Latrobe Valley, which is generally better than in Melbourne" (5, Volume 1, p 16).
SULPHUR DIOXIDE. SO2 readings are very low. Table 1 shows one-hour readings to be a factor of 7 below the comparable Objective levels, while for daily averages the factor is greater.
This is generally consistent with earlier monitoring (4) although occasional higher readings (still well below the Acceptable Levels) were measured before 1978 (5). 97 percent of SO2
emissions in the Latrobe Valley are from power stations (6), so SO2 is a good indicator of power station plume effects.
NITROGEN OXIDES. Both nitric oxide (NO) and nitrogen dioxide (NO2) are monitored although there is an Air Quality Objective for NO, only. NO2 concentrations are also below the comparable objective levels by a factor of 7 except at town sites (Morwell West and Morwell East). 83 percent of NOx emissions are from power stations (6) but the remainder are mainly from low-level sources
which have a disproportionate effect on ground-level air quality, particularly in towns. Even the highest readings shown in Table 1 are well below the required objective levels and this is consistent with all earlier monitoring (4, 5).
CARBON MONOXIDE. As shown in Table 1, the only measurements of CO are those from Morwell East. CO is now also monitored at Moe and Traralagon stations, which have since begun operation. The results in Table 1 are consistent with the long-term record from Morwell East, in which the highest one-hour reading was below the Detrimental Level by a factor of 7 and the Acceptable Level was never exceeded (4, 5).
OZONE. Air Quality Objectives have been set for oxidant, determined by measuring O3. Acceptable and Detrimental Levels have been set for one-hour (0.12 ppm and 0.15 ppm)
and eight-hour averaging times (0.05 ppm and 0.08 ppm). The one-hour Acceptable Level may not be exceeded on more than one day in any year. The eight-hour Objective is based on vegetation damage.
Table 1 shows one-hour averages comfortably below the requirements, but one station (Minniedale Road) did not comply with the eight-hour Acceptable Level. This is consistent with previous analyses (4, 5) which show the eight-hour Objective to be the more stringent. While one-hour Levels are easily met, air quality in the Latrobe Valley is at or about the level set by the eight-hour Objective.
LOCAL VISUAL DISTANCE. Table 1 shows that local visual distance at each station was less than that specified by the Air Quality Objective. A monthly analysis of low LVD is given in Table 2, where the number of days below the Acceptable Level has been divided by the number of stations operating (to the nearest half station- month). Considerable variability from year to year is evident but there is a seasonal variation which produces most days in winter and autumn and least in summer. Low LVD occurrences in Melbourne also show this variation. The average number of days below the LVD Acceptable Level per year per station is 17 for Latrobe Valley rural stations, 34 for Latrobe Valley urban stations and 45 for Melbourne EPA stations (7).
VARIATION WITH WIND. The dependence of average pollutant levels on wind speed and direction has been analysed (8, 9). Table 3 shows typical results, from the Minniedale Road monitoring station. The wind speeds and directions were measured at the monitoring station at a height of 10 m.
Only wind speed and direction categories with a sample size of a least 40 have been tabulated.
Statistical models of air quality often assume that concentration decreases due to the diluting effect of increasing wind speed. There are many exceptions to this behaviour, as is evident from Table 3, most clearly by the increasing concentration of SO: in west winds. The Minniedale Road station is about 20 km east of the power station sources and in lighter winds the power station plumes have sufficient time to disperse, becoming more dilute before they reach the monitoring station. This behaviour is qualitatively consistent with predictions of Gaussian dispersion models. There is little variation of SO2
with winds from other directions.
NOx generally decreases and LVD increases with wind speed in directions away from the power stations, consistent with increasing dilution of
Clean Air/August, 1983
Table 2: Number of Low LVD Days per Month Rural Stations
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1979
9.3 7.6 1.8 0.3 0.5 0 0
1980 0 0 0 1.7 4.2 0.3 0 0.1 0.1 2.1 0.1 0.1
1981 0 0.1 4.0 4.4 1.9 0 0 0
a Morwell West, Moe, Traralgon and Morwell
ground-level emissions with increasing wind speed. In the case of O3, concentration increases almost monotonically with wind speed, possibly reflecting the occurrence of lighter winds at night, when lower O3
concentrations occur.
Occurrences of relatively high concentration can be analysed according to the wind direction at the time of measurement. Taking into account the overall distribution of wind direction, it is possible statistically to determine whether pollutants occur preferentially from certain wind directions. Such an analysis has been performed on the highest 10 percent of SO3, NOx, NO2, NO and O3 readings and the lowest 10 percent of LVD readings at each of ten stations of the LVAMN (10), producing the following conclusions.
Most stations showed SO2, NOx, NO2 and, to a lesser extent, NO and reductions in LVD originating from the industrial and population centres of the Latrobe Valley. Because of the closeness of industry and towns in the area, this type of directional analysis is not able to differentiate clearly the effects of the different sources.
Drainage flows from the slopes of the valley were not found to be frequent mechanism causing elevated pollutant concentrations. At the Darnum North station (the most westerly station — see Figure 1) there was no evidence of transport from Melbourne of any of the pollutants examined. For all stations, the O3 data did not show any preferred direction, suggesting that Melbourne is not a major source of O3 in the area.
VARIATION WITH TIME. Average pollutant levels have been listed against time of day and season and typical results, again from Minniedale Road, are presented in Table 4 (8, 9).
Conclusions about seasonal variation should be tentative as the data only span about one year. NOx
concentration peaks in the early morning and in winter it remains high through the day; summer and spring
(Average of Operating Stations) Urban Stationsa
1979
16 4
1 1 0 0 0
1980 0 0 0 5 0
7
3 11 1.0 3.5 1.0 0
1981 0 0 6.5 7.0 6.3 1.8 1.3 1.0
concentrations are lower than those for autumn and winter. SO2concentration peaks in the late morning and O3in the early afternoon. LVD does not have a regular time of day pattern and the seasonal variation shown in Table 2 is not evident at all stations, possibly as a result of the high variability from year to year.
BETWEEN-STATION CORRELA- TIONS. Correlations between simultaneous readings at pairs of monitoring stations give an indication of the value of information received at each station. If most correlations are high, an individual station does not contribute much more information than could be predicted from the results of the remaining stations. If correlations are low it is possible that additional monitoring stations may be desirable, e.g. to resolve topographical effects.
Correlation coefficients for one- hour average pollutant levels have been calculated (8). A cube-root trans- formation has been used on the raw data so that the few high readings in the highly-skewed distributions will not have a disproportionate effect on the correlations. The data are for different periods for each station, between mid-1979 and mid-1981; in some cases the sample sizes are fairly small. These correlations should therefore be interpreted with caution. Seasonal and diurnal variations and auto-correlation between consecutive readings will contribute to the correlations.
Table 5 shows results for SO and O3. SO2 correlations are low and O3
correlations are high, reflecting the point-source and regional characteristics of these pollutants, respectively. NOx and airborne particulate matter (which is derived from LVD measurements by an inverse relationship) lie between these extremes. NOx correlations are mainly less than 0.5 and none are negative. Correlation coefficients for airborne particulate matter are higher but more variable. Subjective evaluation suggests that the network
45
