Appendix 1 Calculation of Results and Statistics        
        
CONTENTS
Period Covered By Observations
Derivation of Results
Significance of Results
Formulae used in Calculating Concentrations
Formulae used in Calculating Annual Statistics
Units


Period Covered by Observations

The UK Smoke and Sulphur Dioxide Network is operated on the basis of the "Pollution Calendar". The pollution year always begins on the Tuesday nearest to 1 April, and contains twelve months, each of exactly 4 or 5 weeks, all beginning on Tuesdays. Pollution months April to September make up the summer period, and October to March constitute the winter period. The twelve 'months' of observations covered by this report are:

APRIL 97 1 April - 28 April (4 weeks)
MAY 97 29 April - 2 June (5 weeks)
JUNE 97 3 June - 30 June (4 weeks)
JULY 97 1 July - 28 July (4 weeks)
AUGUST 97 29 July - 1 September (5 weeks)
SEPTEMBER 97 2 September - 29 September (4 weeks)
OCTOBER 97 30 Septemer - 3 November (5 weeks)
NOVEMBER 97 4 November - 1 December (4 weeks)
DECEMBER 97 2 December - 29 December (4 weeks)
JANUARY 98 30 December - 2 February (5 weeks)
FEBRUARY 98 3 February - 2 March (4 weeks)
MARCH 98 3 March - 30 March (4 weeks)


Derivation Of Results
 The data have been obtained by computer from daily observations made for the United Kingdom Smoke and Sulphur Dioxide Monitoring Network. The formulae used for calculation of smoke concentrations, ie for relating blackness of the filter to the weight of smoke per unit volume of air samples, are those which have been used for the National Survey Smoke and Sulphur Dioxide tables published since Winter 1961-62. The formula used for calculating SO2 concentrations has never been changed.

As in previous years, the validity of the original readings has been checked by means of an editing program.

Significance Of Results
 It is important to note that in making comparisons of pollution in different towns, careful account must be taken of the details of the sites for which measurements are available in relation to the geographical structure of the town, that is, to the situation, extent and types of industrial, residential and commercial areas. Local variations in fuel type and quality can also have a significant effect on the measurements.

Formulae used in Calculating Concentrations

(a)        Smoke
Smoke concentrations have been calculated by the use of the British Standard Smoke Calibration Curve (BS 1747: Part 2: 1991).
For reflectometer readings of 40 to 99 the following formula is used:

C = F (91,679.22 - 3,332.0460 R + 49.618884 R2 - 0.35329778 R3 + 0.0009863435 R4)
V

where
C = concentration in micrograms per cubic metre
V = volume of air sampled, in cubic feet
F = a factor relating to the sampler clamp size, as follows:
  • 0.288 for 1/2 inch clamp,
  • 1.00 for 1 inch clamp,
  • 3.68 for 2 inch clamp, or
  • 12.80 for 4 inch clamp
R = reflectometer reading
This formula represents the calibration curve to within ± 1.3% over the range of reflectometer readings between 40 and 90. When used to calculate concentrations from reflectometer readings between 91 and 98 the results may be underestimated by as much as 6%.

For darker stains with reflectometer readings between 40 and 20 the formula used is:

C = F (214,245.1 - 15,130.512 R + 508.181 R2 - 8.831144 R3 + 0.0628057 R4)
V

For stains with reflectometer readings of less than 20 this formula gives only an approximation to the concentration, the result being well below the true value. Reflectometer readings of less than 10 are impossible to assess accurately and hence the results are calculated as if the reading had been 10, which at least gives a minimum value. However, such low reflectometer readings, corresponding to very high smoke concentrations, are now rare in the UK.

(b)        Sulphur Dioxide
Sulphur dioxide concentrations have been calculated by the method described in BS 1747: Part 3: 1991. The formula used to calculate sulphur dioxide concentrations is:

C = 4520 m
V

 where
C = concentration in micrograms per cubic metre
m = volume of 0.002M (N/250) di-sodium tetraborate used, in millilitres,
V = volume of air sampled, in cubic feet

Formulae Used In Calculating Annual Statistics

(a)        Arithmetic Mean (AM)
where
AM        is annual arithmetic mean
Ci        is daily concentration for day i
N        is number of results available for the year

(b)        Winter Median (WMD)
Daily concentrations from the winter period (October - March) are sorted into ascending order of concentration value, C1, C2, C3, ...., Ci, ...., CN
If N is even,

or if N is odd,

where
WMD        is winter median
Ci        is ith daily concentration in the ascending set
N        is number of results available for the winter period

(c)        Percentiles (50%, 99%, etc)
Daily concentrations are sorted into ascending order of concentration value, C1, C2, C3, ...., Ci, ...., CN and the associated percentile value for each concentration value is found from
where
Ci is the percentile for the ith concentration in the sorted set, that is, Pi% of the concentrations will be equal to or less than Ci
N is the number of results available for the year

The concentration values for the fixed percentile values quoted are obtained by linear interpolation between the concentration values for the nearest percentile values on either side.
For example, in the sets
P1, P2, ...., Pi, ...., 98.8, 99.3, ...., PN
C1, C2, ...., Ci, ...., 150, 160, ...., CN
the 99th percentile would be 154 µg m-3

Units
 The unit employed for expressing both smoke and sulphur dioxide concentrations from this Network, both in this report and on the disk, is the microgram per cubic metre (µg m-3). However, concentrations of gaseous pollutants such as SO2 are sometimes expressed as parts per billion by volume (abbreviated to "ppb").

For SO2, the conversion factor is as follows:

1 ppb = 2.62 micrograms per cubic metre (for SO2 only) - at a temperature of 25oC and 1013 mb pressure.
1 ppb = 2.66 micrograms per cubic metre (for SO2 only) - at a temperature of 20oC and 1013 mb pressure.

The conversion factor is different for other gaseous pollutants.

Appendix 2 Data on Disk
These data are available from the online Air Quality Archive

Appendix 3 Sites Comprising 'Core' Subset

10003 ABERDEEN 3 1220008 FALKIRK 8 2370002 NEWBURN 2
20005 ACCRINGTON 5 1230008 FARNWORTH 8 2390024 NEWCASTLE UPON TYNE 24
26001 ADDLESTONE 1 1290010 GATESHEAD 10 2390027 NEWCASTLE UPON TYNE 27
69701 ARMAGH 1 1300020 GLASGOW 20 2400026 NEWPORT (MON) 26
85005 ASHINGTON 5 1300051 GLASGOW 51 2414001 NEYLAND 1
90008 ASHTON-UNDER-LYNE 8 1300069 GLASGOW 69 2430007 NORWICH 7
150005 BACUP 5 1300073 GLASGOW 73 2440020 NOTTINGHAM 20
160003 BALLYMENA 3 1300095 GLASGOW 95 2460005 OLDBURY 5
160004 BALLYMENA 4 1300098 GLASGOW 98 2470013 OLDHAM 13
190012 BARNSLEY 12 1305004 GLOUCESTER 4 2533509 PONTEFRACT 9
200004 BARROW-IN-FURNESS 4 1343709 GREENWICH 9 2540007 PONTYPOOL 7
205006 BATH 6 1360016 HALIFAX 16 2551014 PORT TALBOT 14
240010 BEDFORD 10 1370005 HAMILTON 5 2551504 PORTADOWN 4
270013 BELFAST 13 1385009 HARROW 9 2560010 PORTSMOUTH 10
270042 BELFAST 42 1450003 HEMSWORTH 3 2650007 RAWTENSTALL 7
380006 BLACKPOOL 6 1482503 HETTON-LE-HOLE 3 2677503 RETFORD 3
390302 BLETCHLEY 2 1515005 HOLMFIRTH 5 2781510 RUNCORN 10
395005 BOLSOVER 5 1550001 HORWICH 1 2795004 ST ALBANS 4
400024 BOLTON 24 1570019 HUDDERSFIELD 19 2800036 ST HELENS 36
410002 BO'NESS 2 1590006 ILFORD 6 2800043 ST HELENS 43
430006 BRADFORD 6 1633509 ISLINGTON 9 2839001 SCARBOROUGH 1
453003 BRIDGWATER 3 1650011 KEIGHLEY 11 2840015 SCUNTHORPE 15
470026 BRISTOL 26 1685002 KILMARNOCK 2 2870005 SEDGLEY 5
500012 BURNLEY 12 1690019 KINGSTON-UPON-HULL 19 2872505 SELBY 5
507513 BURTON-UPON-TRENT 13 1721006 KIRKCALDY 6 2892502 SHOREDITCH 2
510009 BURY 9 1735007 LAMBETH 7 2940016 SLOUGH 16
530018 CANNOCK 18 1757703 LARNE 3 3027003 STALLINGBOROUGH 3
540012 CARDIFF 12 1790019 LEICESTER 19 3056805 STEPNEY 5
555013 CARLISLE 13 1800004 LEIGH 4 3070005 STIRLING (BURGH) 5
580010 CASTLEFORD 10 1840005 LINCOLN 5 3090020 STOKE-ON-TRENT 20
625006 CHEADLE & GATLEY 6 1845003 LISBURN 3 3170012 SUNDERLAND 12
675018 CHESTERFIELD 18 1850016 LIVERPOOL 16 3220002 SWINDON 2
715006 CHORLEY 6 1950016 LONDON CITY 16 3230007 SWINTON & PENDLEBURY 7
750005 COALVILLE 5 2190011 LONDONDERRY 11 3265013 THURROCK 13
760011 COATBRIDGE 11 2190012 LONDONDERRY 12 3314601 TRAFFORD 1
829004 CRAWLEY 4 2232506 MACCLESFIELD 6 3350026 WAKEFIELD 26
840009 CREWE 9 2233501 MAGHERAFELT 1 3360009 WALLASEY 9
855003 CROSBY 3 2250008 MAIDSTONE 8 3380018 WALSALL 18
915013 DARLINGTON 13 2270002 MALTBY 2 3430017 WARRINGTON 17
930009 DARTFORD 9 2280011 MANCHESTER 11 3470002 WEDNESFIELD 2
960024 DERBY 24 2280015 MANCHESTER 15 3541517 WESTMINSTER 17
1025001 DUNGANNON 1 2280021 MANCHESTER 21 3610008 WIGAN 8
1060007 EALING 7 2281010 MANSFIELD 10 3670002 WOMBWELL 2
1080005 EASTBOURNE 5 2305019 MEXBOROUGH 19 3696009 WOOLWICH 9
1100024 EDINBURGH 24 2310034 MIDDLESBROUGH 34 3700003 WORKINGTON 3
1130012 ELLESMERE PORT 12 2320003 MIDDLETON 3 3732510 WREXHAM 10
1140014 ENFIELD 14 2333501 MOORENDS 1 3750009 YORK 9
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