All local authorities including Hillingdon have had to review their local air quality to assess if the air quality objectives set by the Government will be met. The review and assessment process has been carried out in stages since 1999 as follows:

Stage 1 Review and Assessment

This was an initial simple screening process to identify all the potential sources of the seven key pollutants within the borough. Hillingdon completed its Stage 1 review in March 1999 and published its findings, after consultation, in a report. This concluded that we would meet the objectives for 1-3 butadiene, benzene and lead in all areas of the borough but that we would need to proceed to the next more detailed stage for the other pollutants, namely carbon monoxide, sulphur dioxide, particulates (PM₁₀) and nitrogen dioxide.

Stage 2 Review and Assessment

This was a more detailed study of the remaining four pollutants of concern and required the use of simple air pollution modelling techniques. Hillingdon completed this Stage 2 review in September 1999 and again published its findings, after consultation, in a report. This concluded that we would not meet the objectives for nitrogen dioxide, PM₁₀ and sulphur dioxide and so we would need to proceed to the final detailed modelling stage for these pollutants. During consultation carbon monoxide was raised as a matter of concern and it was therefore decided to also include this pollutant in the detailed Stage 3 Assessment.

Stage 3 Review and Assessment

Hillingdon commissioned Cambridge Environmental Research Consultants Ltd (CERC) to undertake the detailed modelling and assessment of the four pollutants identified as of concern in the borough. The model used was a "new generation" advanced computer dispersion model. This model took into account emissions from traffic, aircraft, industry and all domestic and heating sources. Air quality monitoring from sites around the borough was used to validate the modelling. The results of the work showed that the government objectives for nitrogen dioxide and PM₁₀ would not be met in some parts of the borough. An Air Quality Management Area would therefore need to be designated to tackle the problem.

The Stage 1 - 3 Review and Assessment reports are available for inspection at the Environmental Services Reception, Civic Centre. Alternatively, copies can be ordered via the Environmental Protection Unit.

Stage 4 Review and Assessment

Following the designation of an Air Quality Management Area each local authority is then required to carry out a Stage 4 or Further Review and Assessment of existing and likely future air quality in the area(s) of concern. The intention is that this further assessment is used to define the relative contribution of different pollutant sources within the areas exceeding the objective, so as to allow a focussed Action Plan to be prepared.

Hillingdon's Stage 4 report has been prepared by Ricardo-AEA and concludes the following:

• The 2005 NO₂ objectives are not going to be achieved in some areas of the borough, and are going to be exceeded by a greater amount and over larger areas of the borough than previously expected. However, these changes do not affect more of the population than is already present within the designated Air Quality Management Area.
• The 2004 PM₁₀ objectives are likely to be achieved at all relevant locations within the borough.
• An amended AQMA ordercould be issued, for nitrogen dioxide only.

The full text of the Stage 4 report, and associated documents can be downloaded from here:

• Hillingdon Stage 4 Review and Assessment Report
• Appendix 3 - Air Quality Modelling for West London
• Appendix 4 - Source Apportionment for Hillingdon
• Appendix 5 - Scenario Modelling for Hillingdon

Second Round of Review and Assessment.

In 2003 the second round of local authority review and assessment commenced. The latest round is split into two phases as follows:

1. Updating and Screening Assessment (USA). The objective of this is to identify what may have changed since the last review and assessment, thereby highlighting areas where objectives may be at risk of being exceeded when they weren't previously.

The USA has now been published and concludes that Detailed Assessment (DA) is required for the pollutants nitrogen dioxide and PM₁₀. The full text of the report can be downloaded from here:

• Hillingdon Updating and Screening Assessment, February 2004
• Hillingdon Updating and Screening Assessment, October 2006
• Hillingdon Updating and Screening Assessment, May 2009

2. Detailed Assessment. This will provide an accurate assessment of the likelihood of an air quality objective being exceeded at relevant locations. It should be sufficiently detailed to allow local authorities to designate or amend Air Quality Management Areas.

If an Air Quality Management Area is declared or maintained following the detailed assessment, then, as previously, the local authority will carry out further detailed assessment to confirm the designation.

In addition to these phases of review and assessment, the local authority are also expected to provide fairly simple annual air quality progress reports so that the LAQM process is continuously moving forwards.

It is envisaged that in the future the whole review and assessment process will start with an updating and screening assessment at the beginning of each three-year cycle.