~tmospherir Enuironmenr Vol. 23, No. 2, pp. 509-512, 1989. Printed in Great Britain.

tnxM4981/89 S3.00t0.00 Pergamon Press plc

SHORT COMMUNICATION

A SHORT TERM SURVEY OF DAILY RAINFALL ACIDITY IN THE U.K.

A. PORTEOUS and R. S. BARRATT*

The Open University, Walton Hall, Milton Keynes, MK76AA, U.K.

(First received 1 March 1988 and received for publication 29 June 1988)

Abstract-Short term surveys of rainfall acidity in the U.K. are carried out annually at a very large number of sites throughout the country. The widely distributed and large number of continuing observations provide a unique set of data on spatial variability of rainfall pH. While simple techniques are employed, the data confirm the observations made in other surveys that there is a gradient of increasing acidity from west to east.

Key word index: pH, rainfall, acidity.

The purpose of the present communication is to summarise the preliminary results obtained to date in a national survey of rainfall acidity carried out by over 250 students ammaRy on the Open University course “Environmental Control and Public Health”. The large number of people involved in making the large number of observations provide probably unique information in spatial variability.

RAINFALL MEASUREMENTS

As part of the Home Experiment Kit for the Environ- mental Control and Public Health course, students were provided with three components of a rain gauge. These components were a plastic funnel to collect the rain, a plastic cylinder in which to store it and a m~su~ng cylinder graduated in millimetres of rain collected by the funnel. A pH meter with a combination glass/reference electrode and standard buffer solutions (pH 4 and pH 7) were also pro- vided.

Guidelines on siting the rain gauge inctuded ensuring that it was placed on an open level area, spaced wet1 away from all obstructions by a distance equivalent to at least twice the height of the obstruction above the rim of the gauge. Paved areas, terraces or slopes, walls and roofs were to be avoided, with the preference being an open level area of short grass or gravel. The aim was also to have the rim about 30 cm above the ground.

Before use the apparatus was wiped with a tissue paper moistened with distilled water, and then rinsed with distilled water. This procedure was repeated each day when the gauge was emptied, if it was not actually raining at the time. The gauge was emptied and the catch measured by each student at regular daily intervals, preferably at the same time each day.

The precipitation was decanted into a plastic beaker and the pH value measured with the meter, which was standard- ized each day.

Students measured the rainfall daily as it occurred thereby approximating to event sampling in a similar manner to the U.K. Primary Network. These measurements were made over 30-day periods at an average of 260 sites in the spring seasons of 1986 and 1987. In a recent review of acid deposi- tion, Irwin and Williams (1988) pointed out that annual

*To whom correspondence should be sent.

mean values conceal wide temporal variations. In particular H+ and other ions from non-marine sources exhibit maxima in spring and summer. Fortunately, this period of the year coincides with the programming of this exercise within the student calendar. The surveys are nevertheless short term ones, and this must be remembered when comparing the results with annual mean values published elsewhere. Figure 1 represents the spatial distribution of sites operating in 1987. Different sites are used each year.

RESULTS AND DISCUSSION

Rain is naturally acidic through the solution of CO, in water. This produces the weak acid, carbonic acid, with a natural pH of between 5.6 and 5.8. This is sufficiently acidic to dissolve mineral elements and to make them available in trace amounts for the nutrition of living organisms. However, it is now widely accepted that natural processes produce substances such as SOi- from sea or volcanic sources and which may lower the pH nearer to 5.0 even in rural areas. In many areas closer to human activities, rainfall may have even lower pH values, especially as a result of strong acids produced from fuel use. In the discussion of the present results obtained throughout the whole of the U.K., the pH scale is used.

Summa~es of the pH of rainfall on a daily basis and expressed as an average for each county represented in 1986 and 1987 are given in Table 1. It must be recognized that the experimental approach adopted in this survey is of necessity very much simpler than that advocated in the U.K. Acid Rain Review Group’s Second Report (1987). Few of the criteria set out in that report in relation to both sampling sites and analytical techniques could be imposed on a survey carried out by many hundreds of Open University students. Nor would the stringent quality assurance scheme as described by Heyes et al. (1985) readily be applicable to this type ofsurvey. Nevertheless, it is clear from an inspection of the relative values presented in Table 1 that the data are broadly comparable for the two years. In particular, the parts of the country experiencing similar acidity in rainfall year by year are similar. Thus the least acidic rainfall consistently appears in the west country and in the south, whereas highest acidity is found in the east Midlands and also in the northeast. The U.K. Review Group(1987) reported that over 1981-1985 the areas with the greatest acidity were the East Midlands and East Anglia, and a west to east gradient of increasing acidity was apparent. The pattern is confirmed by the Open Univer- sity data for the spring seasons of 1986 and 1987. The Review

AE 23:2-o 509

510 Short Communication

7 . .

f’ v ‘- 3 ‘-\- - ‘- ’ .!-. , ,RAFFORD-.I .“:__.-’

Fig. 1. Representation of the spatial distribution of rainfall sampling sites in spring 1987.

Short Communication 511

Table 1. Summary of rainfall pH values

County

pH of rainfali samples No. of rainfall events No. of sites Mean SD

1986 1987 1986 1987 1986 1987 1986 1987

Aberdeenshire Angus Avon ~dfordshire Berkshire Buckinghamshire Cambridgeshire Cheshire Cleveland Cornwall Cumbria Derbyshire Devon Dorset Durham Dyfed Essex Gloucestershire Hampshire He~fo~shire Inverness Isle of Wight Kent Lancashire Leicestershire Lincolnshire Lothian Merseyside Mid-Glamorgan Norfolk Northamptonshire North Humberside Northumberland Nottin~amshire Oxfordshi~ Perthshire Shetland Isles Shropshire Somerset Staffordshire Strathclyde Suffolk surrey Sussex Tyne & Wear Warwickshire West Midlands Wiltshire Worcestershire Yorkshire

Other regional values

London Wales Scotland Northern Ireland Guernsey

4.8 0.85 -

6.16 4.87 5.16 5.30 4.82 4.77 6.7 6.14 4.87 7.21 6.08 6.44 5.06

5.02 6.69 5.62 5.47 5.38 5.88 5.32 5.86 5.96 5.55 5.01 5.63 6.12

- 1.12 1.15 0.94 1.07 0.97 0.93 0.66 0.88 0.78 0.46 0.95 0.93 0.95

5.05 5.18 5.61 5.21

_ 0.96 1.23 1.04 0.96

- 6.62 5.63 5.53 4.72 4.97 5.33 5.39 5.12 5.18 5.31 4.77 5.15 4.78 6.31 4.8

5.14 5.47 5.70 5.12 5.16 5.46

5.94 5.10 4.94 4.88

5.57 5.80

::: 5.59 4.59 5.07 5.63

4.84 5.59 5.26 5.00 5.74 5.15 5.59 4.41 4.83 5.15 5.87 5.03 4.94

5.06 5.72 6.08 5.28 5.27 5.38 5.20 5.88 4.76 5.41 5.38 5.62 5.41 5.02

0.74 1.18 0.91 0.65 1.00 0.94 0.99 0.71 0.93 0.91 0.64 0.89 0.77 1.1 0.73

1.09 1.08 1.14 0.80 0.67 1.06 1.13 0.60 0.53 0.87 1.08 0.76 0.95

5.05 5.49 5.05 5.56

5.49 0.90 0.89 213 56 5.42 1.11 0.94 224 250 5.15 0.87 0.89 380 325 5.50 0.88 0.98 269 59 5.87 - 0.98 - 27

0.82 0.81 1.25 1.01 1.23 1.03 0.91 0.89 1.19 1.02 0.86

:::

0.66 0.99 1.17 1.09 0.77 0.98

0.86 1.11 0.95 0.89

1.03 0.85 1.13 1.38 0.89 0.90 1.29 1.03

0.72 1.10 0.89 0.84 0.67 0.83 1.03 1.12 0.89 0.89 0.66 0.79 0.61 0.93

49 _

135 46 81

112 57

123 13 45 32 12

124 58 57

206 41

181 144

21 196 100 99 54 51 83 60 79 59 65 66 93 15 34

71 57 51 80 23

159 166 46 33

119 115 94

327

42 69 31 46 27 40

123 24 58 84 80 78 29

44 139 21

158 52 37

116 128 26 26 _ 77 59 71 12 56 57 41 72 _ 12 38 95 46 43 84 25

113 74 25 70 47 32

183

3

7 2 5 7

;: 1 3 2

: 4 3

12 2

12 8

1 11 7 5 3 3

: 5 3 4 4 6

:

4 3 3

4 11 11 3

3 7

:

13 14 24 15

3 7 3 4 2 3 9 2 4 8 5 6 2

2 10 3

10 5 4 _ 9

10 2 2 - 6

- 1 3 7 4 3 5 3 9 6 2 5 4 3

15

4 11 27 4 2

Group also reported that northwest Scotland had the smal- lest H+ concentrations. The sample populations in that

eastern England, but that the two sites were inadequate to

region from the present study are too small to clarify this define the area. No evidence to support this is found in the

point, but on the basis of the data available, it is the present data analysis.

southwest peninsula and adjacent areas that have highest pH Barrett and Irwin (1984) reported that while data for

values in the country. The Review Group report (1987) southern parts of the country were relativeiy sparse, there

further indicated that an area of higher acidity existed in was an indi~tion of relatively high acidity in the southeast of England. No data to clarify this point were presented from

512 Short Communication

1981-1985 statistics (Review Group Report, 1987), The pre- sent data for 1986 and 1987 do not indicate such an area of high acidity in that region, but do indicate high acidity in the northeast of England. The incidence of certain local vari- ations is apparent in the data. For example, the single site operating in Cleveland in 1986 shows unusually high pH values. This particular observer introduced some quality control by checking calibration against dilute acids and bases to confirm the high readings obtained. The unusual results were attributed to a nearby NH,-works. Similar local effects and variations between neighbouring sites, especially urban and rural, are clearly aspects for further investigation as the survey continues year by year. The data set for 1987 also suggest that the “acid rain” observed by Angus Smith (Benarde, 1987; Irwin and Williams, 1988) over 100 years ago in Manchester is still to be found.

It is encouraging that a mass survey of this type is able to produce data broadly in agreement with those produced according to rigid criteria. Certainly, individual data sets at a site may be subject to systematic error, but relative values are more important than absolute measurements, and the overall agreement between spatial observations in 1986 and 1987 gives confidence in the broad picture. The exercise is to continue in each succeeding year that the course is offered, and it is proposed to introduce precipitation weighting in future years. This will allow for acidity deposition to be surveyed in accordance with Review Group practice. This is an important concept because parts of the country, notably Cumbria and parts of Scotland, experience the greatest rainfall and hence potentially the largest inputs of acidity.

CONCLUSIONS

These initial results of a nation-wide survey of rainfall pH carried out by students on the Open University course “Environmental Control and Public Health” confirm the major patterns reported in the literature. This confirmation is

encouraging when it is considered that the techniques appli- ed in this survey are reIatively simple. However, the large data sets, the widespread national coverage and the agree- ment year by year allow confidence in the overall patterns reported. A decline in pH from west to east across the country is a general pattern, although there are certain exceptions. Greatest acidity of rainfall is found in the east Midlands and in the northeast of England. A great strength of this work is the national coverage which is perhaps one of the most comprehensive and includes many rural and urban areas not previously sampled to any great degree. Hence the data clarify the situation in those parts of the U.K.

More detailed analyses will be carried out on the data presently available and also to be produced by students taking the course in future years. Refinements will be intro- duced as are practicable and will include precipitation weigh- ting and a form of quality assurance

Acknowledgements- -The authors gratefully acknowledge the time and effort of the many hundreds of Open Iiniversity students contributing to this study.

REFERENCES

Barrett C. F. and Irwin J. G. (1984) Acid Deposition over Great Britain, IWPCjIWES Joint Meeting, March 1984, Birmingham, U.K.

Benarde M. A. (1987) Health effects of acid rain: are there any? J. R. Sot. Health 10, 139-145.

Heyes C. J., Irwin J. G. and Barrett C. F. (1985) Acid deposition monitoring networks in the U.K. Standing conference of cooperating bodies, Paper SCCB 105/6, Warren Spring Laboratory, Stevenage, U.K.

Irwin J. G. and Williams M. L. (1988) Acid rain: chemistry and transport. Environ. Pollut. SO, 29-59.

UK Review G~OUD on Acid Rain (1987) Acid deposition in the United Kin’gdom, 1981-85,‘Warren Spring Labora- tory, Stevenage. U.K.