This Instruction Manual has been written for the guidance of participants in the UK Smoke and Sulphur Dioxide Monitoring Network. It is intended as an update to "National Survey of Smoke and Sulphur Dioxide: Instruction Manual", issued in 1966. This updated version covers the operation and components of the 8-port sampler now used at most Network sites, with advice on its installation, operation, and maintenance. It also covers assessment of smoke and sulphur dioxide concentrations from the measurements obtained. However, the old Manual should be kept as it provides useful background information. In particular, the very small number of site operators still using the old single day sampler should continue to refer to the old Manual.

Please note that any references to product or manufacturer names do not imply recommendation or endorsement by AEA Technology or the Department of Environment, Transport and the Regions (DETR).

The UK Smoke and SO₂ Monitoring Network and its predecessor the National Survey date back to the early 1960s, and provide the longest running series of air quality measurements in the UK. The National Survey was set up to monitor the progress of the Clean Air Act; this Act was introduced, following the smogs of the 1950s, to control urban smoke and sulphur dioxide pollution resulting from domestic coal burning. The 8-port sampler was used, an instrument which provides daily mean concentrations of sulphur dioxide and fine suspended particulate (as black smoke). The National Survey was run by Warren Spring Laboratory (WSL), on behalf of the Department of the Environment (now the Department of Environment, Transport and the Regions). Monitoring was carried out by participating organisations, mostly Local Authorities, and data from the Network processed at WSL.

Over the first twenty years of the National Survey’s operation, smoke and sulphur dioxide emissions decreased substantially, reducing ambient concentrations of these pollutants. In 1981, the National Survey was reduced in size, and is now known as the UK Smoke and Sulphur Dioxide Network. The Network now serves two purposes. Firstly, to monitor compliance with the relevant EC Directives on sulphur dioxide and suspended particulate matter. Secondly, to provide a long-term database of smoke and SO₂ measurements to assess trends in concentration and spatial distribution. For this purpose, a "core" subset of sites is used to provide a representative sample of monitoring locations in major population centres throughout the UK, with a wide spatial coverage of the whole country.

Warren Spring Laboratory operated the UK Smoke and Sulphur Dioxide Monitoring Network until their merger with AEA Technology in 1994. Since then, AEA Technology Environment has operated the Network on behalf of DETR and data from the whole period of operation is archived at AEA Technology.

Monitoring is currently carried out at approximately 180 sites in the UK. The sampling equipment is operated by co-operating organisations. These are mostly Local Authority Environmental Health departments, although some other organisations such as colleges also participate. These participants maintain and operate the sampling equipment used, carry out analysis of samples, and send the raw data to AEA Technology Environment on a monthly basis, using a standard format (discussed in more detail in Sections 5 and 8).

The data are processed at AEA Technology Environment, again on a monthly batch basis. Specialised computer software is used to validate the data and calculate ambient concentrations of black smoke and SO₂. A printout of the month’s results is sent to the Local Authority. The daily mean concentrations of black smoke and SO₂, are retained on AEA Technology Environment’s own air quality database. From here, the data are available to the Department of Environment, Transport and the Regions, and on request to other Government Departments, the public, industry, research organisations, schools and colleges. The Annual Summary Report, published each year, has provided one of the main routes for public dissemination of data from the Network. Also, a comprehensive archive of air quality measurements, including those from the Network, is available via the World Wide Web, at web site /netcen/aqarchive/archome.html

Since the original instruction manual was produced in 1966, there have been substantial developments in legislation and standards covering ambient smoke and SO₂ concentrations.

The European Council Directive 80/779/EEC of 1980 set air quality limit values and guide values for sulphur dioxide and suspended particulates. The limit values were mandatory in most parts of the UK from 1 April 1993. The limits are presented in Table 1.1, along with the non-mandatory guide values for reference purposes.

The Network fulfils the statutory monitoring requirements of the EC Directive on Sulphur Dioxide and Suspended Particulates. Each year AEA Technology Environment performs an analysis of all the previous pollution year's data with respect to the requirements of the Directive. This is supplied to the Department of Environment, Transport and the Regions for formal submission to the European Commission.

In the UK, smoke concentrations are calculated according to the British Standard smoke stain calibration. However, the Directive quotes smoke concentrations in terms of the OECD (Organisation for Economic Cooperation and Development) Smoke Calibration Curve (OECD Publication no. 17913: 1964). The relationship between concentration determined using OECD and BS calibration is:

OECD concentration = BS concentration divided by 0.85

The above Directive, 80/779/EEC¹ is to be superceded in future years; the European Commission have issued a Directive on the Assessment and Management of Ambient Air Quality ² - the so-called "Framework Directive". "Daughter Directives" for pollutants including SO₂ and suspended particulate matter are being developed under the "Framework Directive". The first proposed Daughter Directive on SO₂, NO₂, PM₁₀ and lead³ reached Common Position in the summer of 1998. This Directive will contain limit values for these pollutants, aimed at protection of human health and, in some cases, of ecosystems.

The Daughter Directive limits relating to SO₂ are given in Table 1.2 below. These limits are still at the proposal stage, and there may be some change before they come into force.

There is also an "alert threshold" for SO₂ of 500 µg m^-3 (188 ppb), measured over three consecutive hours at representative sites over at least 100 km² or an entire zone or agglomeration, whichever is smaller. Public warnings and advice are to be issued if this threshold is exceeded.

It is clearly not possible to compare data from the Smoke and SO₂ Network with the proposed hourly limit. Nor is it relevant to compare data from this urban network with the annual and winter limits for protection of ecosystems, which are intended for protection of rural areas. However, it is possible to compare the daily data from the Network with the proposed 24 hour limit, for protection of human health.

The Daughter Directive standards for suspended particulate relate to PM₁₀, not black smoke. Therefore, data from the UK Smoke and SO₂ Network are not directly comparable with this Directive. However, the Daughter Directive states that the existing monitoring requirements and standards for black smoke will remain in force until 2005.

The UK National Air Quality Strategy⁴ was published in March 1997. It includes a standard for SO₂, of 266 µg m^-3 (100ppb) as a 15 minute average concentration, and an objective that the 99.9th percentile of 15 minute means is within this value by 2005. The UK National Air Quality Strategy standard applies only to 15 minute means, and does not provide any equivalents relating to daily data. There is also an objective for particulate; 50 µg m^-3 measured as the 99th percentile of running 24 hour means (this in effect means that no more than four days in a full year’s monitoring should exceed this concentration). The particulate objective specifically applies to PM₁₀, not black smoke, and the UK National Air Quality Strategy acknowledges that these two techniques are not the same. However, PM₁₀ is usually higher than black smoke except at very high "episode" concentrations, so if daily mean smoke exceeds 50 µg m^-3, it is likely that PM₁₀ has also done so.

1. Council of European Communities Directive on Air Quality Limit Values and Guide Values for Sulphur Dioxide and Suspended Particulates (80/779/EEC)
2. Council Directive 96/62/EC on Ambient Air Quality Assessment and Management.
3. Daughter Directive for SO₂, NO₂, PM₁₀ and Lead, Common Position Text, 24 Sep 1998
4. The United Kingdom National Air Quality Strategy. The Stationery Office, March 1997. ISBN 0 10 135872 5