A Brief History of AQ Monitoring in the UK

Air pollution has been a problem in the UK for centuries, with doctors and scientists recognising links between air pollution and population health as far back as the 16^th century. Pollution became an increasingly serious problem during the industrial revolution, as coal became increasingly widely used within industry and for domestic space heating. Inner cities, including London, were particularly badly affected.

During this period, it was not uncommon for the combination of pollution and unfavourable weather conditions to cause serious urban smogs. Historic sources suggest that each smog episode could cause thousands of premature deaths in susceptible people. These lethal 'pea-soupers' finally culminated in the infamous smogs of the 1950s and 60s, which finally precipitated both vociferous public concern and decisive Government action.

In response to this situation, the UK Government introduced its first Clean Air Act ^C3 in 1956; this targeted both domestic and industrial coal burning with a range of different emission control and regulatory measures. A few years later, in 1961, the UK established the world's first co-ordinated national air pollution monitoring network, called the National Survey, monitoring black smoke and sulphur dioxide at around 1200 sites in the UK. Following the Clean Air Acts, several further pieces of legislation and additional monitoring networks were introduced to combat and measure air quality in the UK.

As discussed at length in the Air Pollution in the UK 2007 report, the National Survey and its early predecessors was able to monitor over 60 years the dramatic decline in both black smoke and sulphur dioxide concentrations (Figure 1). This historic decline has been due to a number of factors, including fuel switching, the introduction of cleaner fuels and technologies, and successful legislation.

Over recent decades, black smoke levels have remained low; as a result, monitoring of this species has declined, with black smoke now measured in the UK through a monitoring network of just 21 sites. As coal burning has decreased, however, the importance of other pollutants - and primarily those from traffic - has increased. Road transport is currently the dominant source of pollution across the UK - both in cities and sometimes in more rural areas. For this reason, the UK's focus has shifted progressively to the monitoring of pollutants created (directly or indirectly) through vehicular emissions; these include, in particular, ozone, nitrogen dioxide and fine particulate matter.

The earliest air quality measurements used relatively simple, manual techniques. Often a sample would be collected at a site and then returned to a laboratory for analysis. This is, in fact, still a common practice today, due to the relative low cost and high reliability of these types of measurements. However, in the 1970s the UK also introduced automatic analysers to the monitoring networks. These had the benefit of low labour costs and could provide highly resolved, continuous measurements. These continuous measurements became a requirement for regulatory purposes and so, in 1987, an automatic UK urban monitoring network was established to monitor compliance with the emerging EC Directive limit values on air quality. This network subsequently expanded, following commitments by Government to expand urban monitoring in the UK and improve public availability of air quality information.

In 1992, the then Department of Environment established an Enhanced Urban Network (EUN). In 1996, this network expanded following an initiative designed to promote the integration of local authority sites into the national network 1) where this met national monitoring objectives and 2) when appropriate quality and consistency standards could be maintained. At the same time, increased decentralisation in the management and quality assurance of the networks was actively promoted. The net effect of these measures was to substantially increase the number and diversity of stakeholders and participants in the national monitoring effort, thus increasing competition and improving standards.

In 1995, all statutory and other urban monitoring was consolidated into one comprehensive programme. Throughout the next five years, over 50 local authority sites were integrated into the resulting network, including 14 of the London Air Quality Monitoring Network sites. In 1998, the previously separate UK urban and rural automatic networks were then combined to form the current Automatic Urban and Rural Network (AURN), which is the most important and comprehensive automatic national monitoring network; in 2007, this comprised 133 sites, operational for all or part of the year.

The expansion in automatic monitoring is clearly illustrated in Figures 2 and 3, where we show the increase in the number of sites and the total hourly measurements made since the commencement of automatic air quality monitoring in the UK.