Executive Summary
The intention of this report is to carry out a Fourth Stage review and assessment on those pollutants identified in the Third Stage report as likely to exceed the relevant air quality objective. In the case of this authority, this consists of the annual average objective for nitrogen dioxide, which was predicted to be exceeded in 3 areas around the town of Doncaster.
This predicted exceedence resulted in the declaration of 3 Air Quality Management Areas (AQMAs).
Because of the size of the Borough, (the largest geographical metropolitan area in the UK), and the varied nature of the land use within the authority, together with the industrialised nature of the neighbouring local authorities from the south west to the north east of the Borough’s boundaries, compilation of the 3 reports has proved to be a complex task.
The conclusion of the First Stage Review and Assessment report was that a further review and assessment was required for all of the pollutants for which objectives have been set in the Air Quality Regulations (with the exception of ozone, which is not required to be assessed by local authorities).
The Second Stage Review and Assessment concluded that a Third Stage Review and Assessment was required for nitrogen dioxide and particulate matter only.
The Third Stage Review and Assessment concluded that the annual average objective for nitrogen dioxide was unlikely to be met by the relevant date (2005) and that it would be necessary to declare 3 AQMAs. The AQMAs were declared to become operational on the 1st August 2001.
The intention of this Stage 4 Review and Assessment is to reassess the conclusions of the Stage 3 report by taking into account any new national or local policies and developments, information on emission factors etc., and the results of further monitoring.
The prediction of the relevant pollution concentrations, in the years to which the air quality objectives apply, has been achieved by the use of an advanced air pollution dispersion model (Airviro). The accuracy of the model's predictions has been validated by comparing modelled pollution concentrations with monitored concentrations at the point of monitoring.
The possible effects of the Government’s 10 year Transport plan and the opening, ahead of schedule, of the North Bridge relief road (now known as St George’s Bridge) have been taken into account when carrying out the reassessment process.
The Stage 4 review and assessment process has confirmed the findings of the Stage 3 report in respect of Air Quality Management Areas 1 to 3. It has been found necessary to declare a further AQMA around the area of Hatchell Wood, Cantley, around the point where the A638 crosses the M18, due to fact that the annual mean air quality objective for nitrogen dioxide(NO2) was likely to be exceeded.
This has occurred due to the use of the revised vehicle emission factors in the air pollution dispersion model, which have resulted in the 40mg/m3 NO2 contour covering a slightly wider area than previously.
The principal pollution reduction measures that are proposed to be incorporated into the Air Quality Action Plan are listed in this report. No cost benefit analysis has been carried out however. This will be done as part of the Action Plan once consultation on the various proposed pollution reduction measures has been completed.
Results Of Consultation
The draft version of this report was submitted to a number of Government bodies, neighbouring local authorities, local organisations representing industry and commerce, other interested groups and members of the public. In addition, copies of the report were made available at public libraries, the reception areas of council buildings, and a downloadable copy was placed on the Council’s web site.
As a result of the comments received, especially those by the Department of the Environment, Food and Rural Affairs’ (DEFRA) consultants a number of changes have been made to the content of the final report, particularly in the validation method of the dispersion model. The principal changes in methodology are listed below:
- The ratified data from the automatic monitoring stations located within AQMAs 1 and 3 has been used for dispersion modelling purposes, with the caveat that 2 of the 3 stations have not achieved the required 90% data capture rate.
- The results from the diffusion tube site at Church Way have been confirmed as overestimating concentrations by 4.2%. The corrected results, with the bias removed, have been used in the validation process and in the production of the “uncertainty” zones.
- The approach detailed in Appendix B of the NSCA publication “Air Quality Action Plans: Interim Guidance for Local Authorities”, has been used to calculate the required percentage improvement from traffic emissions needed to meet the objective level, rather than the dispersion modelling technique used in the draft report. Close examination of the results produced by the dispersion model, showed that it was not capable of sufficiently allowing for the varying contributions to the overall NOx concentration of the different classes of vehicle when calculating the percentage reduction required, leading to an overestimate in the percentage improvement required.
- In order to illustrate the varying contributions each class of vehicle makes to the Nitrogen Oxide(NOx) emissions from road traffic, tables 20 to 24 have been included. These tables detail the ratio of vehicle type to contribution within each AQMA.
- Re-validation of the model showed that it was over predicting by a factor of 4.8%. Re-plotting the pollution contours for 2005 has shown that although the Carbon Dioxide(CO2)SDM contour did still bisect a greater number of relevant locations, but these were still within the boundaries of the existing AQMAs. There is therefore no need to extend the boundary of AQMA No 2, as was proposed in the draft version of this report.
