CLEAN AIR P.C. Ivin - QUT

(1)

CLEAN AIR

P . C . I v i n

(2)

ALCOA SPECIFIED FOR ANGLESEA;

The Anglesea Power Station of Alcoa of Australia Limited uses 1.2 million tons of brown coal a year to produce 150 Mw of electric power for the company's alumina smelter and semi-fabricating facilities at Point Henry, Victoria. Joy's Western Precipitation Division designed and built the electrostatic precipitators which effectively clean the station's

JOY PROVIDED IT.

flue gases and keep the sky blue over Anglesea.

Western Precipitation equipment has been helping to hold back the health threat of air pollution for 60 years and Joy has the design and manufacturing facilities to produce air cleaning equipment for any industry—including electrostatic precipitators, mechanical collectors, filter type collectors

and wet scrubbers. Western Precipitation Division, Joy Manufacturing Company Pty.

Ltd., 78-86 Kent Road, Mascot, N.S.W. 2020. Tel.: 67 5161.

Offices and plants throughout the world

JOY MANUFACTURING COMPANY PTY. LTD.

Cover ii Clean Air / November, 1971

(3)

Clean Air / November, 1971 Al

(4)

PLASTIC F I L T R A T I O N ELEMENTS

Spacy is a sintered porous plastic material, based on ihe same principle as powder metallurgy, and having a unique porosity property. Spacy keeps a smooth surface which is not affected by wetting or drying and may be cleaned with water or che- micals repeatedly.

Available in Polyethylene, Polypropylene, P.V.C, Nylon, Acrylonitrile-Stylene Copolymer, Methyl-Methacrylate and Cellulose with pore sizes from 3 to 4 0 0 micron.

FOR FULL DETAILS AND SPECIFICATIONS CONTACT —

Box 158 P.O. Epping, N.S.W., 2121

1A, Aiken Rd., West Pennant Hills, NSW, 2120 t

Phone: 871 4336, 871 4335

Shown above: Multiple bench down draft fume extraction/filter system supplied to

major shoe manufacturer.

w h e n t h e

problem's d u s t or f u m e s . .

turn to the experts

DESIGNERS & MANUFACTURERS OF STANDARD & SPECIAL AIR POLLUTION CONTROL EQUIPMENT A N D SYSTEMS.

POLLUTION CONTROL ENGINEERING

4 9 5 COLLINS STREET, MELBOURNE, VICTORIA 3 0 0 0 Telephone: 6 2 4 5 5 1

PTY.

LTD.

Clean Air / November, 1971

(5)

STARTING TO GATHER SMOG DATA?

Selbys are able to supply a wide range of instru- mentation and equipment for this purpose.

The equipment available includes monitoring instruments, recorders, particle collection and analysis apparatus, and complete analysis systems.

Whatever analysis you require N O , N 02, S 02, 03, specific trace hydrocarbons, total hydrocarbons, CO or C 02 - we can supply the appropriate instru- mentation. Using these instruments, continuous or inter- mittent records of atmospheric conditions can be obtained.

The staff at the Selby office in your state wilt be pleased to provide further details.

SO2 Analyser

H. B. SELBY & CO. PTY. LTD.

Melbourne Sydney Brisbane Perth Adelaide Hobart

Clean Air / November, 1971 A3

D.C.E. Filters Clear the Air!

Dust is a powder which can be a pure ingredient returned to t h e manufacturing process, or it can be a nuisance — Dangerous, Toxic, or Poisonous.

D.C.E. Filters Control Dust!

A complete range of Dalamatic and Unimaster Filters to suit many applications such as:- Dust Extraction, Pneumatic Conveying Systems, Venting, Sack Tipping Units to name a few are now available from : —

Jaybee Engineering Pty. Ltd.

P.O. Box 168, Dandenong, 3175

WRITE FOR DETAILS!

(6)

GATX - FULLER PTY. LTD.

221 MILLER STREET. PO BOX 189, NORTH SYDNEY, NSW. 2060

PHONE: 929 9951

AUSTRALASIA

190 HAY ST EAST, PERTH, WA. 6000 PHONE: 25 9955

COMPANIES AND AFFILIATES IN PARIS FRANCE, LONDON, ENGLAND, SAN SEBASTION, SPAIN, HAMBURG, GERMANY, MEXICO CITY, MEXICO, TOKYO, JAPAN, DURGAPUR W. BENGAL, INDIA, MONTREAL AND TOFIONTO CANADA, SAO PAULO, BRAZIL.

Clean Air / November, 1971 Achieve freedom from dust in your plant with Dracco dust control

equipment — there are types for every dry dust problem. Utilized for over 45 years to solve the toughest dust problems.

(7)

V o l . 5 / No. 4 / November, 1971

EDITORIAL, W. Strauss 56 TECHNICAL PAPERS

Some Possible Effects of Aircraft Flying in the Stratosphere,

E. K. Bigg 57 Fibreglass Reinforced Plastics for Industrial Chimneys,

G. McLean 60 Automated Instruments in Air Pollution

M o n i t o r i n g Systems,

B. R. Thiele 65 Programme f o r Environmental Protection in the

European Economic Community 72 FEATURES

1972 Clean A i r Conference 56 News f r o m the Branches 73

Book Reviews 71 Clean Air Society Scholarships 70

JOURNAL OF THE CLEAN AIR SOCIETY OF AUSTRALIA AND NEW ZEALAND President: J.G. Schroder

Federal Secretary: Dr. J. Harry, P.O. Box 163 Lidcombe, N.S.W. 2141 EDITOR

W. Strauss 'Clean Air' is listed in current contents ASSISTANT EDITOR and is published quarterly, in February, J.R. Alonso May, August and November

EDITORIAL BOARD Annual Subscription rates (inc.postage) for W.H. Cock non-members and libraries:

H. Hartmann Australia SA2.50 J. Maher U.S.A. SUS3.50 N. Hawthorn U.K. £1.50p EDITORIAL OFFICE Elsewhere SA3.50 Department of I ndustrial Science Single copies 0.75 cents

University of Melbourne Subscriptions and subscription enquiries Parkville, V i c , 3052, Australia should be directed to the

ADVERTISING Circulation Manager, Mr. W.H. Cock H.E. Pett & Co. 151 Northern Road, Heidelberg 29 Crossley Street, Melbourne 3000 V i c , 3081, Australia

(8)

HORIBA CO ANALYZERS

The Horiba Mexa-200 CO Analyzer is a compact instrument which can quickly and continuously analyze carbon monoxide (CO) contained in automobile exhaust.

Horiba Mexa-200 helps you achieve automobile exhaust tests equivalent to those conducted by Japan's Ministry of Transportation and by the United States Federal Government.

This portable model adopts a very reliable non-dispersive infra-red analyzer known as NDIR method and contains everything necessary for measurement and adjustment.

In the wide Horiba range there's an instrument for every job, from sophisti- cated high precision models to the more simple economy models. Your only problem is deciding which Horiba model suits you best.

S O L E A U S T R A L I A N A G E N T S

A D E L A I D E B R I S B A N E H O B A R T M E L B O U R N E P E R T H S Y D N E Y

YOU COULD REDUCE AIR POLLUTION WITH A BIRRUS VACUUM SYSTEM

If y o u are in a f a c t o r y w h i c h handles p o w d e r s such as ash, c e m e n t , p l a s t e r , f l o u r , coal, or any finely d i v i d e d c h e m i c a l .

One of the c o m m o n e s t sights in i n d u s t r y is p o w d e r b l o w i n g f r o m doorways a n d w i n d o w s , d e s p o i l i n g s u r r o u n d i n g areas.

Inside the f a c t o r y , personnel are often w o r k i n g in c o n d i t i o n s so d u s t y that t h e i r health is i m p a i r e d over a p e r i o d of years. This is all unnecessary — i n s t a l l a B i r r u s fixed v a c u u m cleaning system w i t h c o l l e c t i o n hopper c o m - pletely a i r - t i g h t a n d o u t s i d e the w o r k i n g area.

We shall be pleased to survey your r e q u i r e - m e n t s , a n d p o s s i b l y suggest h a n d l i n g y o u r p o w d e r s or g r a n u l a r m a t e r i a l s in a p o l l u t i o n - free s u c t i o n conveying system.

Bag filter removes all solids from air stream

Receiving hopper of any desired capacity

Power unit exhausts clean air to atmosphere

Fixed pipework inside factory

Hose connection points (self sealing)

BIRRUS ENGINEERING

P.O. Box 4 5 , Mount Waverley, 3149

CO.

Phone: 5 4 4 9 0 2 2

Glean Air / November, 1971 A6

(9)

Journal of t h e Clean A i r Society of Australia and N e w Zealand

VOLUME 5 - 1971

EDITOR: Dr. W. Strauss, Department of Industrial Science, University of Melbourne, Australia.

CONTENTS OF VOLUME 5 TECHNICAL PAPERS

Control of Sulphur Dioxide Emissions f r o m Smelters and Sulphuric Acid Plants,

W. H. Streaen and D. G. Roberts

Current Clean Air Legislation in Australia, P. Le Roy

Victoria's New Environment Protection Act, W. H. Cock

Report on International Clean Air Congress Washington, December 1970,

J. F. Pottinger

Air Resource Management: Planning an Acceptable Urban Environment,

W. Strauss

Air Pollution f r o m Wood Waste Incineration, R. P. Murphy and J. F. Pottinger

Industrial Combustion of Oil Fuels, H. W. Baddams

President's Message: The Future is in our Hands J. G. Schroder

Development of a High Energy Scrubber System for Hot Blast Cupolas,

B. A. Callen

The Memorandum on Chimney Heights and Modern Oil Fired Boilers,

H. H. Macey

Some Possible Effects of Aircraft Flying in the Statosphere,

E. K. Bigg

Fibreglass Reinforced Plastics for Industrial Chimneys,

G. McLean

Automated Instruments in Air Pollution Monitoring Systems,

B. R. Thiele

Programme for Environmental Protection in the European Economic Community

FEATURES

Editorials, W. Strauss 1, 1972 Clean Air Conference 25, 1970 Clean Air Society Symposium

Book Reviews 7, 18, 25, 37,

Branch News 13, Environment Protection Councils

Annual Report, General Meeting and Accounts Clean Air Society Scholarships

2 8 12

14

19 26 31 39

43

49

57

60

65 72

38, 56 38, 56 1 53, 71 55, 73 38, 56 41 70

AUTHOR Baddams, H. W.

Bagg, J.

Bigg, E. K.

Callen, B. A.

Cock, W. H.

Hartmann, H. F.

Le Roy, P.

Macey, H. H.

McLean, G.

Murphy, R. P.

Parberry, D. G.

Pottinger, J. F.

Roberts, D. G.

Schroder, J. G.

Strauss, W. 1, Streamer, W. H.

Thiele, B. R.

18,

INDEX

19, 25, 12,

38,

31 54, 71

57 43 53, 54 37, 53 8 49 60 26 7 14, 26

2 39 56, 71

2 65

(10)

EDITORIAL

Air Pollution: The Long Term Prospects

With larger cities commuting takes longer, and when you wish to relax at that once secluded picnic spot, you will have to share it with many others, each with their portable barbecue.

Another negative benefit is the in- evitable increase in air pollution levels. Of course, not all aspects of a large city are negative; on the positive side are the cultural advantages of concerts, theatres and art galleries, the educational advantages of diversified secondary and tertiary schools and institutes, and the greater range of employment opportunities.

However, can we not plan for a city where we can have nearly all the advantages and minimise the disadvantages?

In Australia there are the large State capitals of Melbourne and Syd- ney, those intermediate size of Bris- bane, Perth and Adelaide, and the small one of Hobart. All of these have much the same educational opportunities of a range of schools, univer- sities and colleges of advanced edu- cation; all have their art galleries, concerts and cultural festivals. The large cities of Melbourne and Sydney are, one feels, too large and have many of the disadvantages mentioned, while the intermediate cities have probably 1972 CLEAN AIR CONFERENCE The Conference Committee, at its last meeting, decided on the following of its Melbourne members to supervise some of the organisational details of the Conference:

Tours and Transportation, Mr. D.

Phillips; Accommodation Liaison Offi- cer, Mr. A. T. Nealis; Registration Desk, Mr. B. Ambor; Preparation of Hand- outs, Mr. R. Andrew;; Public Relations

(Press, Radio, TV.), Mr. L. Clunn;

Visual Aids, Mr. K. Dobson; Notices, Directions, etc., Mr. P. LeRoy; Society Membership, Mr. W. H. Cock; Ladies Committee, Mesdames Clunn, Hart- mann, Gamer, Maher, Phillips and Strauss.

As announced previously, Mr. K.

Dobson is also Treasurer. The Con- venor of the Technical Programme Committee Is Mr. L. J. Garner, Mr. J.

F Maher is the Convenor of the Social Committee, Mr. H. Hartmann is Chair- man and Dr. W. Strauss is Organising Secretary.

In addition to the keynote speakers announced in the previous issue, Pro- fessor M. Treshow, a well known bio- logist from the University of Utah and a world authority on the effects of

reached an optimum size.

The decentralization policies pur- sued by the various States have never attempted to do more than plant a few factories in country towns, and their empty shells, after a few years, are a sad memorial to the futility of this policy. Country towns, which are nearly all quite small, do not present a medium sized industry with a local market, they have the disadvantages of high transport costs and lack of diversified specialized services.

The way this can be overcome, of course, is by the creation of a really large centre, with a population greater than 200,000, and a range of industries and government activities. In Victoria, the State Government has gone some way towards this in declaring six areas for special development, but in the Editor's opinion, even this is too much, and there is considerable doubt whether so many can grow to a viable size in a reasonable time span of, say, twenty-five years. The Labour party policy of establishing centres with a population of 500,000 at certain places e.g. Albury-Wodonga, seems more rational and less doomed to fail- ure.

Air pollution problems are the re- sult of a combination of a lack of control and poor planning. Current trends in State Legislations are over- coming the former, but, so far, there is a lack of effective long term planning on a nation-wide basis.

W. STRAUSS pollutants on plants and Mr. A. E.

O'Keefe, Chief, Air Quality Measure- ment Methods Branch, Air Pollution Control Office, E.P.A., U.S.A., will be giving plenary lectures in their re- spective fields.

A number of stands have been firmly booked for the Conference Ex- hibition, which will show the largest range of pollution measuring and monitoring equipment so far seen in this country, as well as nearly all manufacturers of air pollution control and industrial gas cleaning plant. A special Conference Issue of Clean Air will be published giving details of the range of equipment handled by all exhibitors. It is hoped that this will act as a purchaser's "guide" and directory for industry and government in Australia and New Zealand.

A conference programme and registration form is being included with this issue of Clean Air. Full registration (before 12th April, 1972), is $45 with an additional Ladies Pro- gramme charge of $15 for those who will be accompanied by their wives who are not participating in the technical programme. Early registration is recommended, as a late registration charge of $5.00 will be made for late applicants.

(11)

E. K. Bigg SOME POSSIBLE EFFECTS OF AIRCRAFT FLYING IN THE STRATOSPHERE

To predict the effects of pollution of the stratosphere by aircraft it is necessary to know what particles are now present and what is their origin. Those collected at heights between the ground and about 40 km (130,000 ft) over Australia are described.

Dr. E. K. Bigg is a Senior Research Scientist with Division of Radiophysics, C.S.I.R.O., Sydney, N.S.W:

There is currently considerable interest in the possible effects on the environment of the combustion products emitted by high-flying aircraft.

Gases in the exhaust may undergo photochemical changes and yield particles which, together with solids or liquids also emitted, will add to the particles already present and may have a stratospheric residence time of many years if injected well above the tropopause. Cumulative effects are therefore likely to be much greater than in the lower atmosphere, where the residence time of such particles is measured in days or weeks rather than years. Suffi- ciently high concentrations could reduce the energy of sunlight reaching the ground, particularly in the ultra- violet end of the spectrum, change the stratospheric temperature and alter the sky colour.

Informed opinion on the likelihood of major changes is necessarily de- pendent on a knowledge of the nature and origin of the particles already present in the stratosphere and on a complete knowledge of the photo- chemistry at high altitudes of the exhaust gases, including trace substances. In spite of strongly-worded statements of reassurance by some prominent representatives of the aircraft industry this knowledge simply is not available, and the only honest attitude to take in 1971 is to admit that we have no idea of the probable extent of effects on the environment.

Since early 1968 at the C.S.I.R.O.

Division of Radiophysics, Dr. A. Ono, Dr. Z. Kviz, Mr. W. Thompson and I have undertaken a programmed), (2) to collect particles from all levels of the atmosphere up to about 40 km (130,000 ft.) and to measure their size distribu- tions, concentrations and compo- sitions. This is only a small part of the information required for the predic- tion of the course of stratospheric pollution, but it is an essential part and therefore worth discussing on its own.

As long as 50 years ago it was re- alized that the lower stratosphere must contain a layer of relatively large particles in order to explain the "purple glow" of twilight observed 20 to 30 minutes before sunrise or after s n s e t . However, it was not until 1961 (3) that

they were first collected, by i m p a c t o r s mounted on balloons, in the U.S.A. a n d India and identified as ammonium s u l - phate. While this is a common s u b - stance in aerosols of the lower a t m o s - phere it was not expected t h a t it w o u l d be so common in the stratosphere. I t s presence has been explained in t e r m s of the following sequence: s u l p h u r - bearing gases (SO2 or H2S) from t e r - restrial sources diffuse upwards, a r e oxidized to SO^a by ground-state a t o m i c oxygen (which is present in significant amounts above about 15 km a n d b e - comes more plentiful as one goes higher in the atmosphere), and r e a c t with water vapour to give s u l p h u r i c acid; finally this reacts with a m m o n i a to form ammonium sulphate.

Mossop⁽⁴⁾ in Australia and Friend(s) in the U.S.A. followed this work up with fixed-level collections on p r o b e s mounted on the U-2 aircraft of t h e U.S. Air Force from 1962 to 1964, a f t e r which interest in the subject a p p a r e n t - ly dropped until we started s a m p l i n g again in 1968. The main points m a d e by the earlier investigators were:

1. The layer of particles larger t h a n 0.1/4 diameter is largely confined to altitudes between 15 and 25 km a n d is world-wide.

2. Concentrations of particles l a r g e r than 0.1/t diameter are of the o r d e r of 100 l-¹ at 20 km altitude, m a x i m u m diameters are about 2/t and m e d i a n diameters about 0.3/4.

3. Great changes in the n a t u r e a n d size distribution of the particles at 20 km altitude were found over A u s t - ralia in the year following a m a j o r volcanic eruption on Bali in I n d o n e s i a in March 1963, ammonium s u l p h a t e particles predominating before t h e eruption, and sulphuric acid a y e a r later.

The collection method which we have used is to impact particles on electron microscope screens m o u n t e d on a slowly rotating turntable so t h a t changes with altitude can be observed.

Before examination, the screens a r e placed in a vacuum chamber a n d coated with a thin layer of g o l d - p a l l a - dium alloy by evaporation of t h e s e atoms from a hot wire. The a t o m s strike the specimen at an angle of 3 0 ° ; particles which are raised above t h e surface then leave areas on the s u r f a c e

Clean Air / November, 1 9 7 1 57

(12)

which are free from gold. Because of the extra transparency to electrons of such regions these look like optical shadows when the specimen is examined. The "shadows" appear white and electron-dense regions black in the usual photographic presentation.

Figure 1 shows sequences of photographs of typical particles found in each 5 km band from the ground to 35 km (or the highest altitude reached) on six successive nights. Each

photoghaph is of an region of the specimen and represents the

particle content of the same volume of air at the pressure appropriate to its level. Exceptions are in the top, sixth and seventh photographs of column 1, where, because of very low concentrations, particles from a large volume have been included. The enormous variability in particle types, sizes, and concentrations from one flight to the next, or one level to the next is immediately apparent. In fact it is common to And such large differences between levels only a few hundred metres apart.

This immediately disposes of the notion, which has frequently been expressed in the aircraft pollution con- troversy, that monitoring of the stratosphere would be an absolute safeguard against the effects of pollution. It is quite obvious that large systematic changes could go undetect- ed because of this natural variability.

The chemical nature of the particles has been sought in several ways.

Particles like those in the lower right- hand picture, and all those showing a central particle and satellites, are soluble in water and react with small droplets of barium chloride solution impacted on to them. They are therefore probably sulphates. Rounded particles like those in the lower right picture are unstable in the electron beam and rapidly evaporate to leave a thin cracked shell. This behaviour is typical of ammonia compounds, and the particles are almost certainly mixtures of ammonium sulphate, bi- sulphate and persulphate. Impaction of evaporated droplets of these compounds on to clean screens yields particles identical in appearance to the types commonly found occurring naturally. The rings of satellite droplets about a central particle are readily converted to the same ammonium compounds by exposure to an atmosphere of ammonia, and are quite clearly sulphuric acid, with varying amounts of water and ammonia in combination.

Another method of chemical analysis, and one which is useful in detecting volatile components which evaporate or decompose on descending to the warmer parts of the atmosphere, is to coat the screens with thin layers of reactive substances before they are sent aloft. Figure 2 compares the appearance of sulphuric acid rings on

ERRATA:

Some possible effects of Aircraft Flying in the Stratosphere, by E. K. Bigg

Clean Air, 5 (4) 57-59 (1971) 1. Fig. 2 was printed upside down.

The thin copper film was in the upper photograph not the lower photograph, as stated

26

JUNE JULY DATE 1969

Figure 1. TYPICAL PARTICLES FOUND IN EACH 5 km HEIGHT INTERVAL ON SIX FLIGHTS IN 1969.

EACH PHOTOGRAPH IS OF A SQUARE ON THE SPECIMEN 8u x 8u.

thin films of carbon and copper. Both were exposed at heights near 22 km on 10th March 1970. Reactions of this sort can be compared with those made under controlled conditions in the laboratory and can be made quite specific.

In this way we have established that the dominant particles of the 0 to 10 km region in inland Australia are composed mainly of ammonium sulphates though occasionally some sulphuric acid is found. (It is less common below 10 km than the six flights shown on Fig. 1 suggest). Between 10 and 25 km sulphuric acid is almost ex- clusively found at the present time (mid-1971). It is variable in its wetness (the photographs in the left column of Fig. 1 show the "wettest" groups so far found), in its degree of ammonidation and the highest altitude at which it occurs.

This is very different to the state of affairs in 1961 to mid-1963, when ammonium sulphate predominated at 20 km. Mossop's work suggested that the volcanic eruption of March 1963 on Bali was responsible for the initial

change to sulphuric acid which he found in large quantities in 1964. Evid- ently the balance between sulphuric acid and ammonia was seriously dis- turbed. It is hard to imagine that eight vears later the balance still has not been restored, but we have no way of telling whether the difference between 1962 and 1971 is due to the 1963 eruption, to enhanced volcanic activity in the meantime, or even to enhanced industrial activity.

What effect will aircraft exhaust gases have on these particles? Water vapour is one of the main products and its tremendous affinity for sul- sulphuric acid will certainly ensure that these particles will swell and become more efficient in light scattering. They will also have an increased fall velocity so that to some extent the changes induced will be self-destroy- ing.

It has been argued that the amount of water vapour injected by aircraft will be completely negligible compared to that supplied by a large thunderstorm. This is again a weak argument. Only the most vigorous of

Clean Air / November, 1971 58

(13)

Figure 2.

SULPHURIC ACID COLLECTED ON A THIN CARBON FILM (UPPER PHOTOGRAPH) AND A THIN COPPER FILM (LOWER PHOTOGRAPH). BOTH ARE FROM AN ALTITUDE NEAR 22 km ON 10th MARCH 1970.

spectively, yielding a world-wide m a s s of the order of 10,000 tons ( w h i c h could be wrong by as much as a factor of 10). Since each supersonic flight will add some tons of water vapour in t h e region of highest particle concentration and over a limited range of altitudes, it is clear that in a few y e a r s the particulate mass may increase very considerably just from the effects of water vapour addition alone. T h e particles are already in sufficient concentration to scatter appreciable amounts of light and are in the size range where small diameter increases give relatively large increases in effective scattering cross sections. Against this we must balance the increased fallout rate of the growing particles.

When an adequate world-wide c e n - sus of stratospheric material has b e e n made, calculations should be p e r - formed of the rate of change In stratospheric heating and changes in light-scattering and radiation b a l a n c e caused by given rates of injection of water vapour at the altitudes used by aircraft. Only then will we know If absorption of water by the p a r t i c l e s will have serious effects.

It must be emphasised again t h a t this is only a small part of the w h o l e problem and that it is possible t h a t photochemical changes will be of greater significance. However, e a c h aspect needs to be critically examined, for an error of judgment leading to strong stratospheric absorption of solar radiation would take many y e a r s to rectify.

Acknowledgements

The particle collections m e n t i o n e d were made possible by the generous co-operation of the Balloon L a u n c h i n g Station at Mildura (Department of Supply) and their sponsors, the F a l l - out Branch of the Division of Biology and Medicine of the U.S. A t o m i c Energy Commission. My colleagues Dr. Z. Kviz and Mr. W. Thompson w e r e responsible for the equipment a n d and particle examinations, while t h e Electron Microscopy Unit of S y d n e y University provided the photographs.

storms penetrate the stratosphere significantly — the very large temperature inversion usually present

ensures that — and much of the water introduced will again be carried out in the subsiding air around the clouds;

the remainder will be located near the tropopause and can only proceed upwards by diffusion, against the down- wind flux of hygroscopic particles which will tend to remove it.

59

Although the stratospheric particles are so numerous their small size and the limited range of altitudes which they inhabit means t h a t the total mass is small. Let us suppose t h a t they occur in a 10 km altitude range.

The total volume of this shell of atmosphere is about 5.10" km". Rough estimates of median particle mass (density 1) and concentration in this region are gm and r e -

(14)

FIBREGLASS REINFORCED PLASTICS FOR INDUSTRIAL CHIMNEYS

G. McLean

Fibreglass reinforced plastics (F.R.P.) chimneys have properties which make them more suitable than those fabricated from traditional materials for applications concerning severe corrosion and abrasion conditions. This paper describes the raw materials, manufacturing techniques, design criteria for various applications of chimneys.

Mr. McLean is Marketing Manager for Viking Industrial Plastics Pty. Ltd., Melbourne. He was previously General Manager of R. A. Graydon Beverley, United Kingdom, who pioneered the use of F.R.P. in the field of high temperature and high stress structures. This is part of a paper presented to the N.S.W. Branch of the Clean Air Society, in August, 1970.

2. Since the discussion which appeared on page 59 on the effects of adding water vapour to the stratosphere was written, better data on the vapour pressures over sulphuric acid at low temperatures have become available. It is now clear that an increase of 10% in humidity — which is about the maximum we could expect from a fleet of 500 aircraft operating at an altitude of 20 km — would cause the particles to increase in mass by less than 1%. While the statements as made in the paper are correct, the aspect mass increase is only of minor portance.

18

Introduction: The first recorded use of Reinforced Plastics extends back to the ancient Egyptians. Mummies were protected by varnish, and this material was itself reinforced by cloth bandages. This is ample proof of the durability of the system. Today, the varnish has been replaced by synthetic resins, but the cloth often remains and for some applications it is a very satisfactory reinforcement. In addition to natural fibre fabrics many synthetic materials are utilised to produce laminates with very specific performances.

During the latter part of World War II there was an urgent need for materials to provide streamlining for airborne radar. Fortunately, resear- chers quickly obtained experimental supplies of both polyester and epoxy resins, which are both capable of producing finished products without the use of either heat or pressure. Thus, large mouldings could be made and of types that could not be moulded by machines. These resins were brittle and needed suitable reinforcements.

This radar equipment had to be both a structural unit, and radar transparent. Fibreglass was accepted as the most suitable reinforcing for in- corporating into the resin.

The finished moulding was called a

"Radome" and production commenced almost simultaneously in the USA and Britain. Subsequently commercial work throughout the world in Fibre- glass Reinforced Plastics (F.R.P.) developed.

In Australia F.R.P. was initially used for boat construction, minor motor vehicle components, and roofing sheets. However, today different formulations of reinforced plastics products are available, and these can be

"tailor-made" to achieve specific end products and an extremely wide choice exists.

It is perhaps unfortunate that the product is generally referred to as

"Fibreglass", because engineers tend to think of it as a single material. They would never for example think of

"Light-Alloys" as one material and would in fact choose very carefully from the wide range of light alloys available. Now reinforced plastics are available with much the same range of materials and performance as one

finds with light alloys. Specific formulations of resins, fillers and reinforcements deal with many problems, and one must ensure that the choice of the correct formulation is made.

Materials of Construction

Reinforced Plastics are made by com- bining "cold-set" resins with suitable reinforcing materials.

Resins: These are generally of the Polyester (orthophthalic, isophthalic, bisphenol), Epoxy or Furane types which are all known as "cold-set" resins. This means they require no heat or pressure to cure them. Polyesters are the most used. In appearance and consistency they are similar to honey and a catalyst is used to convert them to a solid. This conversion is carried out slowly, the rate being dependant on the ambient temperature. It is controlled in a reasonably accurate manner, by using varying proportions of accelerator, which achieves conversion

60

(15)

over times varying between 20 minutes and 20 hours.

At the beginning of the conversion at ambient temperatures the resin consistency turns to a gel-like state.

Immediately thereafter the resin temperature starts to rise due to an ex- othermic reaction, and when this action is complete, say after 4 hours, the moulding is "cured".

In order to avoid subsequent de- formation, mouldings are usually left on the mould for a further 12 hours before removal. Actually the curing continues for another 4 days, but it is possible to reduce this by oven post- curing the moulding. For chemical applications it is unwise to use a moulding before one month has elapsed.

Reinforcements: The resins are quite brittle without reinforcement, and it is impossible to use them for anything larger than a small object, such as an ashtray. Reinforcing materials are therefore essential for a larger object.

The most used reinforcement is fibre glass in a variety of forms. During manufacture the glass is drawn into fine filaments and wound onto "chee- ses". From this stage it may be woven into fabric form, with techniques which are the standard practice in the cotton industry.

The most commonly used form of

glass fibre is produced as "Chopped S t r a n d Mat" (C.S.M.). Here the filaments are chopped to lengths of 2 ins.

and dropped on to a moving belt where a binder is applied to make them man- ageable. This produces mats with a standard, amount of glass fibre per unit area with densities such as 1% oz./ft.- and 2 oz./ft.3. By any combination of C.S.M. of a specific weight, laminates are built up to a positive specification. When glass cloth is built up it is essentially "laminate" material. Although plastics with C.S.M. are known as "laminates" they are not in fact true laminates due to the nature of the mats. When correct "lay-up"

techniques are employed the chopped fibres tend to intermingle, and this produces a homogeneous product which is rarely subject to de-lamin- ation problems as sometimes occurs with cloth type fabrics, particularly under impact or vibrationary conditions.

Fabrics made from synthetic fibres can be used as reinforcement but their use is very limited and they can never be used in high temperature work.

Fillers: These are powdered materials which are incorporated in to the resins, to impart specific properties to t h e finished plastics product. Fillers are absolutely essential for improving or achieving the following qualities of t h e resin:

1. Increasing the heat distortion point, and therefore raising the permitted operating temperatures.

2. Reducing the moisture absorption characteristics thus preventing acid or liquid ingress which could be harmful to the reinforcing material.

3. Increasing the stiffness of the product which is desirable from a structural point of view.

4. Providing specific environmental surfaces. Provide a working surface with a particularly high chemical resistance. Providing soft or hard surfaces for abrasion applications. Creat- ing barriers to ultra-violet light and improving pigmentation.

5. Improving the thermal insulation properties or alternatively improving the thermal transmission characteristics of the plastics.

6. Increasing the ability to carry continuous compressive loadings.

7. Control expansion, warping, distortion and shrinkage either in the moulding or operational stages.

8. Improve the quality for most electrical applications.

9. Improve the weathering qualities.

This is a function of 2.

The amount of filler used in a formulation varies according to the application. It should rarely be less than 30% by weight of the finished mix. and is often 50%. Occasionally for extreme resistance to say abrasion the filler/

resin ratio could be as high as 3 : 1.

Filler proportions below 30% effect little change on the resin character-

istics, and their use is of limited value.

Certain fillers used are extremely hard, and under conditions of flexing can cut through the reinforcements, thus reducing the strength of the product. It is therefore imperative that structural units are built with soft fillers and all stress calculations should only take into account the plastics materials with soft fillers. Often the exposed part of the laminate is built with hard fillers and the structural material is then applied to it.

Another important myth exists concerning fillers.

Use of fillers does not necessarily cheapen the product. While some mixes produce lower cost mixes others often increase the mix cost, all of them considerably increase the labour cost of impregnating the glass fibre. Two essential ingredients for making filled laminates are superb mixing of the filler into the resin and first-class im- pregnation techniques, neither of which are inexpensive.

Producing a Moulding

The finished product generally has one smooth surface which is specially produced and designed to be in contact with the working fluid. The other surface, which is normally in contact with the air is finished to an imper- vious rough cast condition, not unlike unfinished concrete. A moulding is produced from a single surface mould, which may be from a variety of materials: steel, plastics, aluminium, hardboard (commercially known as masonite), timber, plaster, etc. If a mould is to be used often then it must be well made and is relatively expen- sive.

For "one-off" jobs the mould is made as cheaply as possible, and is often deliberately destroyed in remov- ing it from the moulding.

The finished mould is firstly well polished and to this surface a parting agent is applied, generally in liquid form. After this a "gel-coat" is applied.

This is the resin mix without glass reinforcement and its thickness should be 0.010-0.015 ins. When this has part- cured, a second "gel-coat" is applied, this time with a very fine glass tissue incorporated. Again when this has part cured the glass mats of given density are applied one by one and the resin mix is impregnated through the glass. This operation must be a continuous one and continues until the specification is complete. It is also good practice to have inspection going on throughout this stage. In the case of very large mouldings the operation can be stopped for an overnight period but the catalyst/accelerator system must be adjusted accordingly.

Certain techniques, known as

"spray-up", can be used. Machines are

61 Clean Air / November, 1971

(16)

available from which the resin is sprayed continuously, and the glass fibre is chopped and induced into the resin stream, and deposited on the mould.

This technique should never be used where stress carrying products are required as the glass distribution is subject to operator skill and is therefore suspect. Only by considerably

"over-building" can one be sure of its load carrying capability.

In order to be specific it is therefore necessary to use Fibreglass of given density.

Another technique sometimes used for cylinders is known as "Filament- Winding". Continuous filaments, glass cloth and mats, are wound onto the mould and the resin is continuously applied with the glass. This technique also gives strict control on the glass distribution and it produces a very high strength product. For chimney applications filament winding equipment which produces a helical pattern should not be used for continual sway is present and there is a tendency to break down the helical wound pattern and this gradually leads to a great loss of strength.

Resin/Glass Ratios

More glass in a laminate gives a stronger material. It is quite possible to make laminates with a resin/glass ratio of 1/1, but it is the resin which provides the chemical resistance, and the glass fibre therefore needs protection. Thus much higher resin/glass ratios than 1:1 are needed, and in practice it is found that the maximum

amount of glass is 30%. Normally laminates with glass contents between 25% and 30% are used. The fibreglass reinforcement in the resin can be considered to be analogous to the steel reinforcement in reinforced concrete, the resin would be the cement, and fillers the aggregate.

As with reinforced concrete, the size, direction and ratio of the reinforcing material can be varied to suit the application, but other factors enter into the choice of the resin/glass ratio, that of the stiffness and ability to withstand high temperatures. Thick laminates are required to give rigidity, and this compensates for the reduced strength obtained with the less than 1 : 1 ratio.

Design Considerations for Filled Formulations

Physical Properties: Because of the wide range of formulations available, precise figures cannot be included here.

When one produces a moulding the production of the moulding can be controlled very accurately; however, it is noticeable that during physical test programmes a high degree of scatter occurs between the various test pieces.

The range of scatter can be as much as plus or minus 10% of the average readings.

Tensile values (see Table 1), are in the order of 18,000 lbs. per square inch and the compression value end to end on the laminate is a little higher. Face to face compression values are in the range of 40-60,000 p.s.i. The shear values are substantially lower at around 25% of the tensile figure, and one must accordingly bear this strongly in mind when designing structures.

The "E" value is very low compared with metals and a typical value would be 1,500,000 p.s.i.

The coefficient of expansion varies considerably between the various

formulation of resin and fillers, but is precise for each mix. It can generally be assumed to be double that of mild steel. It follows that extreme care should be taken in dealing with expansion problems.

This is of great importance with tall guyed chimneys. The chimney is fixed at the base and expands upwards.

It is necessary to set the guys with the chimney cold and this is done on a visual basis. Afterwards each guy is extended by a calculated amount to produce the correct setting of guys with the chimney operational. This necessity often dictates the maximum height to which one can build guyed units. Obviously the guy system must provide stability with the chimney in both hot or cold conditions. If a tall chimney (say 150 ft. or more) is to operate near the permitted maximum temperature then it may well be that with the chimney cold the guys system will permit intolerable movement in wind. When this occurs plastics chimneys need supporting in steel or similar towers.

Where ductwork joins a chimney it is often necessary to fit expansion joints. These are also made in reinforced plastics of which several designs are available.

Temperature Limitations: The material itself will permit a maximum gas temperature of 550°F to be used continuously and will tolerate up to 600° F on a short term basis. However, these limits have to be applied with discretion. The essential consideration is the amount of stress developed in the particular structure. Where chimneys or flues are mounted in such a manner that they can expand freely and no outside force such as wind have to be considered, then the maximum gas temperature can be used. This is nearly always true of self standing units as well, but it may be necessary to reduce the permitted temperature due to the wind effects at maximum speed.

With relatively small guyed chim-

(17)

neys (i.e. up to 150 ft.) it is nearly always possible to operate up to the maximum temperatures, but with tall guyed chimneys (above 150 ft.) each case requires special study, the critical factor being the stress developed by its own weight and the additional stresses as the guys restrain movement under heavy wind loads.

Specific Gravity and Weight of Structures: The specific gravity obviously varies considerably according to the specification used, but can generally be taken as 1.73 (see Table 1).

This is approximately 65% of the S. G.

of Aluminium of steel.

In practice the weight of a structure in plastics would be equal to that of Aluminium and about 25% of a steel structure to similar designs.

Fire Resistance: Most formulations are resistant to fire in a limited sense, and have self-extinguishing properties. Spontaneous combustion is not possible so that the fire must be applied to the product and as soon as the original fire is eliminated the induced fire dies out quickly. The plastics materials after a fire suffer from a mild charring and sometimes the glass fibres are exposed. In any subsequent fire these tend to produce a fire shield which gives very great fire protection.

During a fire the laminate has only a small drop in strength due to the elev- ated temperature and it maintains its structural properties. The material has no thermo-plastic properties and it does not, as is sometimes supposed, simply melt after the temperature limits have been exceeded.

Repeated fire applications do not appear to materially alter the performance of the product. Under very high temperatures the material is gradually degraded into a fibrous and powder like condition, and this requires temperatures in the order of 800°C to accomplish complete destruc- tion.

It is possible to add fire retardant material to the formulations but this considerably lowers the possible operating temperatures. Recent evidence indicates that even when fire retardant materials are incorporated, they cease to be effective after three years.

This period is for ambient temperature laminates and at higher operating temperatures the effective period is reduced considerably.

Around 500 boiler chimneys have been built, many of which come directly off the smoke box, and it is a fact that a number have had minor fires in them, without reduction in their working life.

Guys: Four flights of guys in plan should be used, particularly on tall chimneys, as three guys in plan permit too much movement.

Spacing of the guys vertically is an important consideration and the guy attachment points should be steel

bands bonded to the chimney and wrapped in reinforced plastics.

Guy ropes of galvanised marine standing rigging are recommended, but must be protected by a lightning conductor for they have a sisal core.

Slenderness Ratio: For guyed chimneys a height/diameter ratio of 40 : 1 appears to be a practical maximum and 30 : 1 for self-standing units.

Effects of High and Low Temper- atures: Changes in temperature have a substantial effect on the strength of the finished product. Testing is normally carried out at ambient temperature. As the temperature rises to the maximum permitted all values will fall off progressively to 75% of the original values. Conversely as the temperature falls to -110°F the strength values increase by about 25%. All properties seem to improve as the temperature is reduced and at no stage in the high/low range does the material become brittle.

Long Term Drop in Strength: In order to find what changes take place after extended operation the author has physically tested offcuts from plant which had become redundant or required modification in some form to establish authorative data of changes which had occurred.

In general, it was found that in chemical works for stacks operating at lower temperature there is a drop in strength, over a period of about 3 years, of 20%-25% of the original values. After this no practical further deterioration in strength has been observed up to 7 years.

With high temperature applications, over an initial period of 2 years, a drop in strength of up to 30% has been recorded followed by an increase of about 15% in the next year giving a net loss of 15% in the long term. After the 3rd year the conditions are stabilised.

Self-Induced Forces: Fibreglass Reinforced Plastics have very high self-dampening qualities and there appears to be no problems regarding self-induced destructive vibrations which are evident with traditional materials at low wind speeds.

Connections to Chimneys: It is essential to avoid breaking into chimneys above the foundation point.

Where connections of this type are required then it is better to raise the foundation by means of a pedestal and to bring in all connections on the underside of the pedestal. This may not be entirely necessary with small chimneys of up to say 25 ft. but it is imperative with larger units.

Many Venturis have been built in plastics to fit into or on top of chimneys of traditional construction and these are extremely effective. They considerably improve the gas exit conditions and in the case of external

Venturis entirely eliminate down- wash. They can have the effect of increasing the chimney height by as much as 30 ft. in normal weather and by 2 ft. to 3 ft. in extremely high winds. Where existing chimneys are oversize they can be used to give suitable exist velocities.

A well designed venturi need put no extra pressure drop on the system and will operate purely on the natural lift available through the chimney.

Air Bleeds: Draught stabilizers are often fitted to F.R.P. chimneys for exactly the same reasons they are fitted to traditional chimneys and we do not consider these to be air bleeds.

There are many cases where high temperature and very corrosive conditions exist together, and if the temperature is above the limit for the plastics then means of cooling the gases should be considered. The applications in mind are those where traditional methods of chimney building would not produce satisfactory results or where the extension of existing units is necessary.

For cases like these air bleeds, an oversize chimney is required with the base flared out to produce a venturi style cold air inlet. The gases are then introduced into the venturi via a nozzle fabricated from traditional materials and nearly always of steel.

The plate thickness should always be excessively oversize to allow for wast- age by corrosion. The inlet nozzle and venturi should be correctly sized so as to accelerate the cold air to the speed of hot gases at the point where they meet. The chimney should be oversized accurately to produce a pre- determined mixed temperature.

Heat Shields: On some installations

(18)

where it is necessary to have a "T"

junction into a chimney it may toe desirable to incorporate a heat shield on the chimney wall in line with the entry duct. This shield would normally be a simple piece of plastics in semi-circular form inserted into the chimney from the base and of sufficient length to cover the change of direction area. This shield prevents

"hot-spots" on the chimney side and absorbs the shot blasting effect of grit.

Because the shield is not able to lose heat by radiation, degration may occur necessitating occasional replace- placement of the shield and provision should be made for this possibility in the design.

Condensate Collection: Due to the smooth glass-like internal surface of the chimneys the condensates run to the bottom of the chimney and it is desirable to drain these away via a down pipe to a seal tank. If the chimney is mounted directly off the boiler then a collection ring should be fitted as low down as possible and the condensates drained away from this point.

Condensate collection is of very great importance where gas firing is used and will be even more important with natural gas due to the large amounts of water vapour given off.

Foundations: The chimneys are extremely light in weight and in the case of guyed units, where the guys deal with the overturning moment, the foundation requirements are extremely simple. Often enough the existing floor is sufficient but the most that is required is a simple concrete slab of 6 inch thickness, lightly reinforced and slightly larger than the chimney or pedestal under consideration.

For self-standing chimneys the

situation is different. The foundation required has to deal with the same overturning moment as a traditional chimney and because of the low weight of the plastics a heavier foundation is required to compensate for the weight differences.

Chimney Extensions: When an existing chimney made of traditional materials requires extension it is often necessary to incorporate guys in the system. On older chimneys it is often impossible to find accurate details of their foundations so one has to assume that it is only sufficient for the chimney as built. Where guys are used it is necessary to incorporate into the clamping arrangement sufficient masonry to cater for the shear forces involved.

Modest extensions can be built without guys and in this case an amount of masonry should be clamped into the system at least equal in weight to the foundation required for the extension itself.

Thermal Insulation: The plastics material can be considered as having semi-insulation properties. It is not a particulraly good insulating material but it does not conduct heat very well either. The "U" and "K" values vary substantially with the mixes( see Table 1), used and the loose descrip- tion given explains the situation.

Resistance to Air Flow: For calculation purposes one uses the standard resistance charts for steel, but actually, due to the extremely smooth in- terior finish, the resistance is lower whilst the ductwork is clean. Obviously when the ductwork or chimney becomes fouled then the resistance is the same as any other material. The build- up takes a longer time to form and

can often be knocked off by hammer- ing the unit.

Standards: Manufacture of industrial units such as chimneys, ducting, pipework and tanks is covered by the United States National Bureau of Standards, Voluntary Product Stand- ard PS-15-69 for Custom Contract- Moulded Reinforced Polyester Chem- ical Resistant Process Equipment.

Other guide lines such as chimney heights, gas velocities, wind loadings, etc., are covered by various Local and State Government Authorities.

Future Developments

With the evolution of improved resins and alternative forms of reinforcement (such as carbon fibre) the horiz- on of reinforced plastics is limited only by the mind of the fabricator and design engineer.

It is imperative that both design engineer and fabricator build within the known and proven properties of the material and relate their activity to the relevant codes, such as PS 15-69 mentioned previously. At the moment FRP is capable of building 300 ft.

0 in. long ships, 1,000 ft. 0 in. high chimneys and 100 ft. 0 in. clear span structures, such as bridges or build- ings. Although the cost of FRP products sometimes prohibits their use, as a general rule the larger the unit the cheaper it becomes when compared with traditional materials, thus the above examples are technically and commercially viable.

In short, any application which requires fine chemical resistance coupled with light/weight/high strength then reinforced plastics should be investig- ated as an alternative to traditional materials.

(19)

B. R. Thiele AUTOMATED INSTRUMENTS IN

AIR POLLUTION MONITORING SYSTEMS

This paper is based on one which was delivered at the Technicon International Symposium in Sydney on February 7th, 1971.

Mr. Thiele is Senior Chemist in the Queensland Division of Air Pollution Control.

Introduction: In planning a monitoring programme, two questions must first be considered. What pollutants should be monitored, and how can this monitoring best be done? A most re- warding study can be made of the ex- perience gained in those major over- seas cities which have suffered air pollution incidents. It becomes apparent that there are several unique patterns of pollution, depending on the geography, meteorology and industry of the area. In those European cities in which these incidents have occurred, the major pollutants have been shown to be particulate material and sulphur dioxide, with metal fume and fluorides sometimes present in quantity. Atmospheric oxides were usually not present at all. In Los Angeles an entirely different pattern has been found. Here, the pollution was almost entirely photochemical in origin, with motor vehicle hydrocarbons providing raw materials, rather than industrial or domestic fuel burning equipment.

Sulphur dioxide has not been a problem. Other cities have provided a picture somewhere between these two.

The United States Continuous Air Monitoring Programme (CAMP) lays down the following pollutants as fundamental to a monitoring programme :

Total Fallout.

Suspended Particulate Material.

Sulphur Dioxide.

Carbon Monoxide.

Oxidants (ozone and peroxy nitro compounds).

Nitrogen Oxides.

Hydrocarbons.

To this list may be added Aldehydes, Hydrogen Sulphide or other compounds whose presence is regarded as locally significant.

The suspended particulates may be analysed for fluoride, nitrate, sulphate and ammonium ions, arsenic, beryl- lium, bismuth, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel, selenium, tin, vanadium and zinc. Asbestos, boron and silicates may also be collected for analysis.

Meteorological parameters such as wet and dry bulb temperature, wind direction and velocity, barometric pressure, sunlight and precipitation

must be considered. Whenever possible information concerning temperature inversions should be collected, since these have almost invariably been associated with air pollution incidents.

In the United Kingdom, a National Survey of Air Pollution is conducted, under the control of the Warren Spring Laboratory, one of the research stations of the Ministry of Technology.

Daily measurements are made at over 1,000 sites, covering fallout, suspended particulates, 24-hour sulphur dioxide levels, as well as long-term sulphur dioxide averages by the lead peroxide candle method.

Analysis of Air Pollutants

"Fallout", as its name suggests, covers those particles which are coarse enough to settle out of the atmosphere under their own weight. It is measured, following collection in deposit gauges. These may be quite sophistic- ated, as the British Standard pattern(¹) — or quite simple, as what is frivolously referred to as the Aust- ralian Standard pattern; a six inch glass funnel mounted in a one gallon bottle. For all its simplicity, this is quite effective, and far cheaper to produce than the British Standard pattern.

"Suspended Particulate Material"

may be defined as solid material of low particle size (say, less than 10 mic- rons) which tends to hang in the atmosphere, and not fall to the ground until the particles agglomerate. It is monitored by drawing air at a known rate through a paper filter and measuring the dark spot produced by transmission or reflectance densitometry.

Results have been expressed in terms of an arbitrary unit known as the COH (Co-efficient of Haze) unit, which has been defined as "that quantity of particulate matter which produces an optical density of 0.01 on a filter paper". Smoke concentrations are re- ported as "COH units per 1,000 linear feet of air drawn through the filter paper". Gruber and Alpaugh defined

"dirt shade" by calculation of "Re- flectance Units of Dirt Shade" or

"RUDS", and used this as a measure