Sheffield cares for air in its complex city

Sheffield City's urban environment presents a complex challenge when it comes to managing air quality. Richard Hill and Mark Daly outline how the council is rising to the task

Effective air quality management requires an ability to juggle a multitude of tasks, particularly in a complex urban environment such as the UK's fourth largest city, Sheffield in South Yorkshire.

Sheffield City Council's environmental strategy department has to balance the requirements for regular reviews of air quality within its region with its commitment to the difficult task of improving air quality. It hopes to achieve this by addressing the key cause - emissions from road traffic. Figure 1, which shows the photo-chemical smog formed over the city, illustrates the scale of the problem.

The management of air quality requires local authorities to assess both the concentrations and spatial distribution of air pollutants. The technologies available to achieve this present something of a dichotomy. Monitoring equipment, when used correctly, can measure concentrations of air pollutants accurately, though only at specific locations.

The mathematics of accuracy
Conversely, mathematical models provide the ability to map pollution concentrations across entire urban areas, although the multitude of assumptions they are based upon means they are seldom able to achieve the accuracy of monitoring devices.

Sheffield City Council combines air pollution monitoring and mathematical modelling using the iAirviro air quality management system developed by the Swedish Meteorological & Hydrological Institute (SMHI) which is supplied through Westlakes Scientific Consulting (WSC). An advantage of this system is that it is internet-based, allowing air quality officers access from any PC running Microsoft Internet Explorer. The server does not need to be located in Sheffield and is hosted at WSC's offices in West Cumbria.

Software and hardware support and maintenance is provided by WSC and SMHI. This is important as air quality data is collected continuously from seven multi-pollutant monitoring stations. Meteorological data required by the computer models is collected from an instrumented mast at the Sheffield Athletic Stadium. Data is automatically uploaded by iAirviro three times a day, with work in progress to allow the data to be accessed through the council's website.

Modelling of air pollutants is required to predict air concentrations at locations distant from monitoring equipment. And future predictions of changes in air pollution have to be taken into account. Further requirements include the assessment of impacts of new planning developments and ensuring the effectiveness of air quality action plans (AQAPs).

Predicting air concentrations
The iAirviro system includes models to predict air concentrations across a range of spatial scales, from street-canyons to the meso-scale transport of pollutants from surrounding regions. However, high quality information on the sources of air pollutants is paramount to the accuracy of modelling assessments.

Sheffield City Council has constructed a detailed emissions database containing approximately 900 road links and 340 point sources. In addition, numerous 'grid' and 'area' sources are used to model diffuse emissions - such as those from domestic fuel burning and waste management sites.

Figure 2 shows the modelled spatial pattern of nitrogen oxide emissions. Emissions of nitrogen oxides and their conversion to nitrogen dioxide in the atmosphere have been the cause for the council's declaration of air quality management areas in the centre of the city and along the M1 corridor. The diagram also provides a graphical illustration of the importance of road sources in the overall emissions of this pollutant, with the road transport network clearly identifiable.

Partnership working
Having determined the areas where air quality problems exist, along with the dominant pollution sources, leads to the question of how improvements may be made. Working in partnership with local stakeholders has enabled the development of AQAPs, which identified a number of initiatives.

These included improving public transport such as bus and rail services and increasing pedestrianisation and cycle lanes. The reduction of vehicle emissions could also be achieved through enforcing emissions testing, promoting cleaner vehicles and reducing motorway traffic speeds.

One of the most challenging areas to address is the provision of information to the public so that they can take action to help improve air quality. South Yorkshire's clean air campaign - www.Care4Air.org - was set up by Sheffield City Council in partnership with four South Yorkshire LAs and the South Yorkshire Travelwise campaign, which promotes more environmentally-aware transport.

Together they raised awareness of air quality, providing advice on how individuals and organisations can contribute. The website is in its second year of operation and is already showing benefits, with 21 companies having won awards for their commitment to clean air. Care4Air set out to provide information in a non-technical way for the public, and an evaluation of the campaign's effectiveness is underway.

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