ANSWERS TO FAQ

General

Air Quality Management Areas

Exposure

Industry & Point Sources  

Modelling & Monitoring

Domestic Sources

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GENERAL

*only applicable in England

The Government is committed to giving local authorities freedom and flexibility as to how they plan to improve their services. As part of this process, an order under section 6 of the Local Government Act 2000 will remove certain statutory plan requirements for authorities rated as excellent in the Comprehensive Performance Assessment.. The order amends the Environment Act 1995 to the effect that excellent authorities will no longer be required to produce an air quality action plan, where they have AQMAs. Those excellent authorities with AQMAs will still, however, have to take action towards meeting their air quality objectives.

 With regard to “non-excellent” local authorities, The Local Government White Paper “Strong Local Leadership – Quality Public Services, issued in December 2001, stated in paragraph 4.30 – “We (Her Majesty’s Government) will no longer require the production of a separate air quality management action plan where an air quality problem arises because of transport pollution. Instead, councils will be free to address this through their local transport plan (LTP).

Non-excellent authorities with AQMAs that primarily relate to local transport issues are recommended to integrate their action plan into the LTP at the earliest opportunity in the LTP cycle. Further information is available in the Policy Guidance PG(09).

In the majority of cases, the appraiser will try to contact the local authority prior to the appraisal being completed in order to discuss any points of concern, or to seek clarification..  In cases where the concerns are significant, it may prove necessary to include commentary within the appraisal report setting out what additional work the authority needs to undertake in order to satisfactorily complete the Review and Assessment report.

Where such concerns arise, the local authority may be required to provide further information or evidence of what was done. .

Where an authority wishes to seek clarification on the findings of the appraisal, it should in the first instance contact the Review and Assessment Helpdesk to discuss the matter with the person who carried out the Appraisal. It could also submit its concerns to Defra, the Welsh Assembly Government, The Department of the Environment NI, the Scottish Government, or the GLA in writing. This should be done as soon as possible after the comments are received.

In Scotland the Scottish Government and SEPA have been liaising closely with each Scottish local authority as the review and assessment process has progressed. This process will continue. (23 November 2004)

Section 84 of the Environment Act 1995 and article 13 (b) of the Environment (Northern Ireland ) Order 2002  provides that, once it has designated an air quality management area (AQMA): "a local authority … shall be under a duty …to prepare a written plan…for the exercise by the authority, in pursuit of the achievement of air quality…objectives in the designated area, of any powers exercisable by the authority."

The explanatory note to the Air Quality Regulations 2000, Air Quality (Amendment) Regulations 2002 and the Air Quality (Northern Ireland) Regulations 2003 state that: "an action plan…will have to be prepared setting out how the authority (district councils (and prescribed relevant authorities in NI) intends to exercise its powers in relation to the designated area in pursuit of the achievement of the prescribed objectives".

i. carried out appropriate reviews and assessments of air quality as required by section 82 of the Act and in Northern Ireland article 11 of the Environment (Northern Ireland) Order 2002;

ii. designated any necessary air quality management areas as required by section 83 of the Act and in Northern Ireland article 12 of the Environment (Northern Ireland) Order 2002; and

iii. drawn up appropriate action plans as required by section 84 of the Act and in Northern Ireland article 13 of the Environment (Northern Ireland) Order 2002.

Where the Secretary of State (in Scotland, the Scottish Ministers and the Department of the Environment in Northern Ireland) is satisfied that an authority has adequately discharged its duties, but, despite this, the objectives are not likely to be achieved:

i. the Secretary of State, the Scottish Ministers or the Department of the Environment in Northern Ireland  may consider what further measures are needed at a national level to ensure compliance with the objectives;

ii. the Secretary of State, the Scottish Ministers or the Department of the Environment in Northern Ireland  may consider the possible role of other agencies or government departments in Northern Ireland (including the Highways Agency and environment agencies) in delivering the objectives.

Box 2.2 of LAQM.TG(09) states (Step 1) that: “if the background concentration is more than that measured then project forward using the approach in paragraphs 2.02 to 2.08”  The reference to these paragraphs is a typographical error.  The reference should be to paragraph 2.12. 

The approach you should take is as follows:

1) identify the mapped background value for the year in which the measurement was taken.  This is value A.

2) identify the mapped background for the year to which you are projecting.  This is value B.

3) divide value A by value B.  This gives the adjustment factor (factor C).

4) multiply your measurement by value C to give the predicted concentration in the future year.

(20 July 2009)

There is no strict definition and the term has different meanings when used in different contexts.  For example, Box 7.1 discusses the different source components of the total nitrogen oxides concentrations.  It differentiates between those components of the background which come from regional sources, and those components which come from local sources.  Thus, in this context, “local background” is a sub-component of the total background concentration.  Conversely, Box 7.2 gives an example of calculating the required reduction in road nitrogen oxides emissions.  Here the term “local background” refers to the entire mapped background concentration at the receptor; with the word “local” used to clarify that the background must be local to the receptor.

Box 7.1 also refers to the “regional background”.  This is the component of the total background that does not come from local sources.  It is represented by the “rural” column in national background maps.   (20 July 2009)

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Air Quality Management Areas (AQMAs)

Pollutant concentrations may vary significantly from one year to the next, due to the influence of meteorological conditions, and it is important that authorities avoid cycling between declaring, revoking and declaring again, due simply to these variations.  Before revoking an AQMA on the basis of measured pollutant concentrations, the authority therefore needs to be reasonably certain that any future exceedences (that might occur in more adverse meteorological conditions) are unlikely.  For this reason, it is expected that authorities will need to consider measurements carried out over several years or more of the national trends in emissions, as well as local factors that may affect the AQMA, including measures introduced as part of the Action Plan, together with information from national monitoring on high and low pollution years.

As a hypothetical example, an AQMA was declared in 2005 on the basis of modelling predictions, which indicated a maximum annual mean nitrogen dioxide concentration in 2005 of 43 µg/m³ .  Monitoring commenced at a worst-case relevant exposure location in 2006, for which an annual mean of 41µg/m³ was measured.  Concentrations declined in 2007 to 38 µg/m³, but no decision was taken at this stage to revoke the AQMA due to the uncertainty in future year concentrations.  Further monitoring in 2008 and 2009 confirms annual mean concentrations below the objective.  The AQMA would then be formally revoked in 2009 following a Detailed Assessment that confirmed a significant downward trend in concentrations. (5 April 2004)

·         it has identified the need for new or additional AQMAs in its area which have to be designated under section 83(1) ( in NI article 12 of the order) ; and

·         it has identified the need to extend an existing AQMA boundary and has to vary the original order under section 83(2)(a) ( in NI article 12 (4) (a) of the order).

The 1995 Act and the Environment (Northern Ireland ) Order 2002 defines the Further Assessment as "supplementing such information as [the authority] has in relation to the designated area in question". The degree of thoroughness of the further assessment will therefore depend upon the information the authority has already accrued about the area to be designated.

If there is only to be a minor extension to an existing AQMA order, such as the encompassing of a few additional buildings or the inclusion of a road junction, as long as the authority has access to substantial information about the area of the extension or can reliably extrapolate from information it has about the area originally designated, Defra and the Devolved Administrations would not expect that authority to have to undertake an extensive Further Assessment. (In some circumstance this may be a simple reference back to the previous further assessment report).

In the case of an extension to an existing AQMA, where an order is varied by a more substantial change, such as going from a few streets to a whole borough designation, the authority would be expected to undertake a more comprehensive Further Assessment.

In either case, the local authority will have to inform the statutory consultees of the findings of this additional Further Assessment.

Where necessary, local authorities should consult the Review and Assessment Helpdesk for specific advice on how extensive their further assessment should be in each case. (4 September 2002)

It is not the case that AQMA designation means that there should be no new development inside the area. Such an approach could sterilise development, particularly where, for example, authorities have designated (or intend to designate) their entire areas as air quality management areas.

When a local authority, however, is considering an application for a development inside, or near to, an actual or proposed AQMA, air quality must be taken into account. In reaching its decision, the weight an authority attaches to air quality relative to other factors will, of course, vary from case to case, depending on local circumstances. More weight, for example, may need to be given to air quality considerations where a development would have a significant, adverse impact on air quality inside, or adjacent to, an air quality management area than where the air quality effects of the development itself are likely to be minimal. Local authorities will be best placed to take these decisions in the light of local circumstances.

All applications for development inside AQMAs should be supported by sufficient information to allow a full consideration of their likely impact on local air quality. It is therefore important that developers are aware of the existence of any AQMAs. It may be appropriate in some circumstances for the developer to fund mitigating measures elsewhere inside the AQMA to offset any increase in local pollutant emissions as a consequence of the proposed development, or to pay for the purchase of monitoring equipment. These measures could be introduced through planning obligations.

In considering whether a site inside an AQMA is an appropriate location for new housing, local authorities may also wish to consider by how great a margin the air quality objectives are currently exceeded, and when they are forecast to be achieved.

PPS23, (CLG's Planning Policy Statement on planning and pollution control) has been published and is available online. In Scotland, Planning Advice Note (PAN) 51, Planning and Environmental Protection is due to be revised. In Wales, planning policy for improving air quality is contained in Planning Policy Wales (PPW) issued in April 2002.(23 November 2004).

Section 83 of the Environment Act 1995 and in Northern Ireland article 12 of the Environment (Northern Ireland ) Order 2002 requires an authority to "by order designate as an AQMA…any part of its area in which it appears that those…objectives are not…likely to be achieved within the relevant period". It does not, however, explicitly state what should be contained in an order.

LAQM.PG(09) recommends that the order should include a map and a description of the AQMA. The EPUK’s guidance note ("Air Quality Management Areas: Turning Reviews into Action") sets out examples of descriptions as follows:-   An example for a larger AQMA might be "an area bordered on the north and east by the council’s own boundary, on the south by a line 50 metres to the south of the A45, and on the east by a line 50 metres to the east of the B1108". For a smaller AQMA, a more detailed description listing individual streets or other physical features might be appropriate. In some cases, it may be appropriate to list the individual properties affected, although there is no legal requirement to do this. Alternatively, it might be useful to include in the order an approximate summary of the number and type of properties affected. This information should be readily available from the review and assessment reports.

Authorities are therefore under a clear duty to review and assess air quality, and, where appropriate, designate AQMAs, wherever people are likely to be regularly exposed. It is not possible to exclude locations from the review and assessment process on the grounds that only a few people are likely to be exposed there. Nor is it possible to prescribe a minimum size for an AQMA, as the policy guidance (LAQM.PG(09), LAQM.PG(S)(09), LAQM.PG(W)(09) and LAQM PG NI (09) ) makes clear. This means that for the purposes of all stages of LAQM, including AQMA designation, isolated cottages are relevant locations.

Once an AQMA has been designated, however, the following approach is recommended in circumstances where the costs of remedial action are likely to outweigh any potential benefits:

1. Further Assessment of air quality inside the AQMA - if it is clear that the road is the primary cause of the problem (as seems likely in these cases), little further monitoring should be necessary. A rough assessment of the costs and benefits of various possible solutions should be summarised in the report of the further assessment.

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EXPOSURE

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INDUSTRY & POINT SOURCES

Where industrial sources are likely to make a significant contribution to the breach of an AQS objective, Local Authorities should contact the Environment Agency, SEPA or NIEA to determine whether there are any planned reductions in emissions which will enable the objectives to be achieved. If this is not the case then these sources should be considered as potentially significant sources for review and assessment.  (Updated 22 June 2009)

Box 5.6 of LAQM.TG(09): Calculation of effective stack height, states: “The stack height should be assumed to be equal to the actual (physical) stack height unless: The height of release is greater than 3 m above the building on which it sits but less than 2.5 times the height of the tallest adjacent building”. This isn’t very clear. For example, what should I do if my stack is less than 3m above the building on which it sits, and does the tallest adjacent building include this building?

The reference to “3 m” in Box 5.6 is unnecessary. The important criterion is whether the stack is less than 2.5 times the building height. The tallest adjacent building should include the building on which the stack sits. To clarify, the following wording should be read as a replacement to the first three lines of Box 5.6 of LAQM.TG(09):

If the actual stack above ground height is less than 2.5 times the height of the building to which it is attached or any other building within a distance of 5 times the stack height above the ground then it will be necessary to calculate an effective stack height following the calculation given in box 5.6 of LAQM.TG(09). If the stack height is more than 2.5 times the building height then the effective stack height is equal to the actual height of the stack above the ground.

To give an example, a stack rises 2 m above the roof line of the building it stands on. This building is 12 m high, so the stack height is 14 m above the ground. This is clearly less than 2.5 times the height of the building (2.5 times the height of the building would be 12 m x 2.5 = 30 m) so the effective stack height is calculated. This is 1.66 x (14 m - 12 m) = 3.3 m.

When you use the nomograms for biomass combustion that are provided in LAQM.TG(09), you must first calculate a “background-adjusted emission rate”.  This takes account of the headroom between the local background concentration and the relevant objective.  For PM₁₀ this is relatively straightforward following the guidance given in paragraph 5.78.  For nitrogen dioxide, the calculation is complicated by the fact that emissions will be expressed as NOx, but the objectives are for NO₂.  Paragraph 5.81 of LAQM.TG(09) gives the following equation dealing with annual mean NO₂ concentrations:

             E_A = E / (40-G)

where E_A is the background-adjusted emission rate, E is the emission rate of NOx in g/s, and G is the annual average background NO₂ concentration in mg/m³.

Similarly, paragraph 5.84 deals with the 1-hour NO₂ objective with the following equation:

             E_A = 40 x E / (200 - 2G)

again, where E_A is the background-adjusted emission rate, E is the emission rate of NOx in g/s, and G is the annual average background NO₂ concentration in mg/m³.

An alternative approach to using the published nomograms is to use the spreadsheet tool provided on the air quality archive website: (http://www.airquality.co.uk/laqm/tools/biomass_calculator_tool6.xls).

This tool performs all of the necessary calculations for the user and gives a “target emission rate” which is the actual emission from the stack.  It does not require any further adjustment.   (Updated 20 July 2009)

When considering nitrogen dioxide, should I assess biomass combustion emissions against the annual mean objective or the 1-hour objective?

You should assess against both objectives.  Box 5.8 of LAQM.TG(09) refers you (at Step 3) to paragraphs 5.81 and 5.84 which explain how to calculate a background-adjusted emission rate for comparison with each objective.  These paragraphs then refer you to the annual mean nomogram in Figure 5.20 and the 1-hour nomogram in Figure 5.21. 

Some authorities have experienced some confusion since Box 5.8 itself (at Step 5) refers them to Figure 5.20 but not to Figure 5.21.  This is an omission in Box 5.8.  The correct approach is to refer both to Figure 5.20 and to Figure 5.21, as set out in paragraphs 5.81 and 5.84.  (Updated 20 July 2009)

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MODELLING & MONITORING

The main purpose of LAQM reviews and assessments is to trigger the designation of AQMAs where necessary. It is essential that, before designating an AQMA, an authority should be reasonably confident about the quality of its monitoring data. But it is also important that authorities make reasonably rapid progress towards the completion of a Detailed Assessment where necessary. This is a difficult balance to strike, since even with twelve months or more of monitoring data, it is not always possible to be absolutely certain whether or not an objective is likely to be achieved and thus whether or not AQMA designation is required. The key test is one of reasonable confidence in the data. The informal guidance published by Environmental Protection UK (formerly the National Society for Clean Air and Environmental Protection (NSCA)) contains some useful advice on dealing with uncertainties when defining the boundaries of AQMAs (copies are available from EPUK, http://www.environmental-protection.org.uk/assets/library/documents/AQMAGuidance.pdf).

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PLANNING & AIR QUALITY

It may also be appropriate in some circumstances for the developer to fund mitigating measures elsewhere inside the AQMA to offset any increase in local pollutant emissions as a consequence of the proposed development, or to pay for the purchase and running of monitoring equipment. These measures could be introduced through planning obligations. Examples might include the funding of better public transport links or other transport infrastructure improvements in the vicinity of the development where a need for such improvements has arisen as a consequence of that development.  In Northern Ireland similar arrangements may be provided under article 40 of the Planning (Northern Ireland ) Order 1991.

In considering whether a site inside an AQMA is an appropriate location for new housing, authorities should consider where, within the AQMA, likely exceedences have been identified and by how great a margin the air quality objectives are currently exceeded, as well as when they are forecast to be achieved. It may be that in some cases, housing developments might best be delayed until the relevant air quality objectives have been achieved or the layout modified to avoid the area of the exceedence. (7 Feb 02)

Local Development Frameworks (LDFs) comprising the development plan documents  set the strategic framework for development in an area over the medium to long term. They can therefore play a key role in minimising the environmental impact of potentially polluting developments, and in ensuring that residential or other sensitive developments are not sited close to existing, or likely future, sources of pollution.

Environmental considerations should play a key role in the drawing up of development plan documents. LDFs/Development plan documents should take account of the findings of air quality reviews and assessments, and in particular of the location and extent of any AQMAs or other areas where air quality is likely to be relatively poor, in determining suitable locations for residential and commercial development. They should include policies on air quality, and ensure that land use allocations have regard to their potential air quality impacts.

Regional Spatial Strategies can also provide a basis for addressing the cross-boundary nature of air pollution. In England, PPG11: Regional Spatial Strategies (2004) advises that RSS/LDFs should take account of the AQS and national air quality objectives and air quality strategies , as well as other factors, in advising on the location of regionally significant development. In Scotland, PAN 51, Planning and Environmental Protection, provides similar advice. RPG can also help improve air quality by, for example, promoting policies which will reduce the need to travel and which will promote the use of public transport. (23 November 2004)

Local authorities, and in Northern Ireland the DOE Planning Service, will be best placed to decide on the appropriate balance between different policy objectives in each case, taking all other factors into consideration. In the longer term, of course, local authorities can help facilitate the redevelopment of urban centres by improving air quality there and thus helping to make them a more attractive place to live or work. (7 February 2002)

Planning obligations are agreements between developers and local planning authorities or are unilateral undertakings by developers. They are used where a proposed development would, if implemented, create a need for particular facilities or would have a damaging impact on the environment or local amenity or would adversely affect national or local policies. When such concerns cannot be resolved through the use of planning conditions it will usually be reasonable for planning obligations to be sought through agreement or offered through a unilateral undertaking, to overcome these difficulties. Planning obligations should only be sought where they are necessary, relevant to planning, directly related to the proposed development, fairly and reasonably related in scale and kind to the proposed development, and be reasonable in all other respects. A planning obligation may, for example, fund better public transport links or other transport infrastructure improvements in the vicinity of the development because a need for such improvements has arisen as a consequence of that development. (7 February 2002) .

The Environment Agency strongly favours environmental permit applications being considered in parallel with local planning applications. The Environment Agency and the Local Government Association have already signed up to the general principle of parallel tracking, as set out in their Planning Protocol.

The authority should declare an AQMA at this location, as Section 4(2)(a) of Air Quality Regulations 2000 and the LAQM Technical Guidance clearly state that consideration must be given to pollutant concentrations at locations outside a building.  If the geographical extent of the exceedence area has previously been set out within a Detailed Assessment or a Further Assessment, then no further work would be required.  If the authority had not previously included this area within a Detailed Assessment (as there was judged to be no relevant exposure) then a Detailed Assessment/Further Assessment would be required.

A local authority could also use a Section 106 agreement under the Town and Country Planning Act 1990 to improve air quality or offset the subsequent environmental impact of the proposed development in the AQMAs (see 1.50 of PPS 23).

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PM₁₀

Yes – it is possible to compare the concentrations measured by the FDMS analyser and the TEOM

In simple terms, the FDMS analyser is based on a TEOM, but incorporates additional components that measure the semi-volatile fraction.  The FDMS analyser reports these two fractions separately.  The non-volatile PM₁₀ mass fraction reported by the FDMS (known as the PM₁₀ FDMS_Base) provides a comparable, although not identical (the TEOM operates with a manifold temperature of 50°C whilst the FDMS operates at 30°C), parameter to the TEOM. 

A comparison of the PM₁₀ FDMS_Base with the TEOM during these equivalence tests yields the following relationship: 

TEOM*1.3 = PM₁₀ FDMS_Base + 5.826 

e.g. if the PM₁₀ FDMS_Base concentration were 20 µg/m³, the equivalent concentration reported by the TEOM (corrected using the 1.3 factor) would be 25.8 µg/m³ 

(2 November 2006)

A small error in the VCM model equation has been identified by King’s ERG, and was corrected on 28 April 2009. This error concerned the temperature and pressure correction applied to the reported TEOM concentrations. This resulted in an underestimation of the TEOM_VCM concentration of approximately 4% at background locations in 2007. At the worst-case locations (kerbside and roadside sites) the VCM model underestimated annual mean concentrations by about 2.5 µg/m³.

Ideally, all concentrations calculated by local authorities using the VCM model before the 28 April 2009 should be recalculated. However, this error is unlikely to be critical unless the calculated annual mean PM₁₀ concentration was above 28 µg/m³ (14 µg/m³ in Scotland).

To help local authorities with this process, the most recent correction Excel spreadsheets that have been generated using the VCM Web Portal have been regenerated and can be downloaded from the VCM web portal.

Further information can be found at http://www.londonair.org.uk/london/asp/news.asp?NewsId=VCMwebportal

(6 May 2009)

A number of local authorities have now completed their Updating and Screening Assessments and have identified poultry farms that meet the criteria (as set out in the Technical Guidance (LAQM.TG(09)) that would require proceeding to a Detailed Assessment.

It is recognised that the screening criteria in TG(09) have been based on limited data, and it was stated that further information would be provided as and when new information became available. To assist this process, three local authorities in England have been awarded Air Quality Grant funding in order to carry out studies at the poultry farms they have identified, in order to assess both the local risk of exceedences of the air quality objectives, and to provide additional information to verify, or amend if necessary, the current screening criteria.

Until this assessment work is completed, there is no requirement for local authorities to move forward to a Detailed Assessment at this time. Where local circumstances (such as a history of nuisance complaints related to the farm in question) suggest that it would be preferable to proceed to a Detailed Assessment as soon as possible, authorities are advised to contact the Review and Assessment Helpdesk in order to ensure that any work carried out is in line with best practice.

Where the outcome of the Updating and Screening Assessment has identified a need for a Detailed Assessment for one or more poultry farms, then the Review and Assessment Helpdesk will have been in contact to obtain further information on their location(s). If authorities in this situation have not been contacted they should get in touch with the Helpdesk at the earliest opportunity.

As these processes are likely to be permitted by the Environment Agency, local authorities should always ensure that their local EA officer is aware that the farm has been identified in their USA as a potential issue.
 

(1 February 2010)

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NITROGEN DIOXIDE

Guidance for England and Wales

             English & Welsh Regional Traffic Growth and Speed Forecasts

English and Welsh Regional Traffic Growth and Speed Forecasts (RTFs) provide the basis for scaling forward traffic flow data within England and Wales.  These forecasts provide both national and regional growth estimates for the country.  Air Quality Consultants Ltd has published an ‘Automated Traffic Growth Calculator for England and Wales’ which provides growth factors derived from the RTFs.  This calculator can be obtained from:

http://www.uwe.ac.uk/aqm/review/mfaqfiles/RTF-Automated-Traffic-Growth-Calculator-v3-1.xls

The original RTFs, published by the Department for Transport, can be obtained from: http://www.dft.gov.uk/pgr/economics/ntm/AF07_Annex_Baseline_summary.xls

The RTFs are divided by vehicle class and are provided for a range of area types (large urban, other urban, inter urban, rural and all areas) and road types (motorway, trunk, principal, minor and all roads).  If it is unclear which of these area or road types is most appropriate to the area of interest, and there is no local advice available from colleagues, it is suggested that all areas or all roads is used as default.

RTFs provide national and regional data, which do not focus upon local levels.  Since traffic volumes are likely to grow at different rates in different localities, it is necessary to refine the RTF factors.  TEMPRO provides the data required for this local adjustment.

            TEMPRO

TEMPRO takes account of local planning data to provide factors which, when used in conjunction with national or regional traffic growth forecasts (e.g. the RTFs), can provide very local traffic projection factors.  It is important to note that TEMPRO should not be used on its own to provide growth projections.  It should always be combined with national or regional forecasts.

The TEMPRO programme and guidance for its use are available at www.tempro.org.uk.  For instructions on how to download and install the programme see the bottom of this note.

NB. TEMPRO data do not apply in Northern Ireland.

            How to Perform the Calculations

This section describes how to perform the calculations.  A worked example is given at the end.

Step 1

Download the ‘Automated Traffic Growth Calculator for England’ and appropriate datasets for TEMPRO from the links given above.

Step 2

Follow the instructions provided with the ‘Automated Traffic Growth Calculator for England’ in order to obtain traffic growth factors for the desired future year.  Factors are provided for a range of vehicle classes and for ‘All Traffic’ (for use when traffic splits are not available in the original data). 

Step 3

Open the TEMPRO Programme.  The front page of TEMPRO has two windows; ‘Datasets Available’ and ‘Chosen Datasets’.  The ‘Datasets Available’ window should contain a number of regional datasets downloaded from the TEMPRO website (see end of this note for instructions on downloading these datasets).  Click on the desired regional dataset and drag it to the ‘Chosen Datasets’ window, and click ‘Proceed to Selection Screen’ under the ‘Actions’ tab.  On the ‘Selections Screen’ ensure ‘Trip Ends by Time Period’ is selected in the ‘Trip Purpose’ box.  Under ‘Area Definition’ select ‘Geographical Area’ and click ‘Edit’, which will take you to a new screen.  Place a tick in the box next to your region, then expand the ‘+’ symbol next to this box.  Find the precise area (or areas) that is/are most appropriate for your data and place a tick in the accompanying boxes.  Exit this screen by selecting ‘Return to Selection Screen’ in the ‘Actions’ tab.  Ensure that ‘All purposes’ is selected under the ‘Trip Purpose Definition’ box, and under ‘Time Period’ highlight ‘Average Day’.  In the ‘Base Year’ box, select the year during which the traffic was counted, and in the ‘Future Year’ box, select the desired future year.  In the ‘Transport Mode’ box, ensure that only ‘Car Driver’ is ticked, and in the ‘Trip End Types’ box select the ‘Origin/Destination’ button.  Click on ‘Proceed to Results Screen’ under the ‘Actions’ tab, which will generate an ‘Origin’ and ‘Destination’ growth factor for the selected region and area(s).  Average the ‘Origin’ and ‘Destination’ factors for each to calculate a ‘Regional TEMPRO factor’ and a ‘Local TEMPRO factor’.

Step 4

Adjust the RTF factor obtained from Step 2 for local growth derived from TEMPRO, as follows:

RTF factor x (Local TEMPRO factor / Regional TEMPRO factor) = Final Growth Factor

Step 5

Multiply your original traffic flow data by this final growth factor to calculate future traffic flow data.

            Worked Example

For a location in Nottingham, you have total vehicle flow in 2005 of 10,000 v/d (AADT) and wish to predict the flow in 2008.

1.  Nottingham is located in the East Midlands region and is best described as a ‘Large Urban’ area.  Using the ‘Automated Traffic Growth Calculator for England’, select 2005 from the ‘Base year’ drop down menu, and tick the ‘Area’ box.  From the drop down menus select ‘East Midlands’ under ‘Region’, and ‘Large Urban’ under ‘Area’, then click ‘GO’.  This gives an RTF factor for ‘All Traffic’ in 2008 of 1.0577.

2.  Using TEMPRO, ensure that the correct selections are made on the ‘Selection Screen’ and calculate a Regional TEMPRO factor, using East Midlands (‘EM’) as the region and a Local TEMPRO factor, using ‘Nottingham(main)’, which is the most appropriate area in this case.  This gives a growth factor between 2005 and 2008 for East Midlands of 1.044 (average of ‘Origin’ and ‘Destination’ factors) and similarly for Nottingham(main) of 1.045.

3.  Finally, the RTF factor from Step 1 can be adjusted for local growth derived from TEMPRO to give a final local growth factor, as follows:

RTF factor x (Local TEMPRO factor / Regional TEMPRO factor)

            1.0577 x (1.045 / 1.044) = 1.0587

The final local growth factor is thus 1.0587

4. Multiply your flow in 2005 by this final local growth factor:

            10,000 x 1.0587 = 10587 v/d

Guidance for Scotland, Wales and Northern Ireland

RTF data are only provided for England, and thus for traffic flows in Scotland, Wales and Northern Ireland, the previous method for scaling traffic data with National Road Traffic Forecast (NRTF) factors should still be applied.  Air Quality Consultants Ltd has published an ‘Automated Traffic Growth Calculator for Scotland, Wales and Northern Ireland’ which provides growth factors derived from the NRTF factors.  This calculator can be obtained from:

www.uwe.ac.uk\aqm\review\mfaqfiles\NRTF-Automated-Traffic-Growth-Calculator.xls

The original NRTF factors, published by the Department for Transport, can be obtained from:

http://www.dft.gov.uk/pgr/economics/ntm/ntmdatasources/nrtf1997/onalroadtrafficforecasts3014.pdf (Table 2A)

The NRTF factors are divided by vehicle class and are provided for a range of growth levels (low, central and high).  If it is unclear which of these growth levels is most appropriate to the area of interest, and there is no advice available from colleagues, it is considered that central growth is likely to be the most appropriate selection.

NRTF factors provide national forecasts, which do not focus upon local levels.  Since traffic volumes are likely to grow at different rates in different localities, it is necessary to refine NRTF factors in Scotland and Wales.  TEMPRO provides the data required for this local adjustment in Scotland and Wales.  TEMPRO does not however apply to Northern Ireland.

In order to perform the calculations using NRTF factors, the instructions provided in the ‘Guidance for England’ section under ‘How to perform the Calculations’ can be followed using the ‘Automated Traffic Growth Calculator for Scotland, Wales and Northern Ireland’ and NRTF factors in place of the ‘Automated Traffic Growth Calculator for England’ and RTF factors.

It should also be noted that should your area of interest be in Northern Ireland, ‘Step 3’ and ‘Step 4’ (relating to TEMPRO growth factors) are not required.  The final growth factor used in ‘Step 5’ to adjust your original traffic flow data, would therefore be the NRTF factor alone.

Guidance for Downloading and Installing TEMPRO

These instructions refer to TEMPRO Version 5 (V5.0 and V5.1), and to most recent versions of MS Windows.

N.B.      Using TEMPRO involves installing new software onto your computer.  You may require authorisation for this (e.g. if you have an IT manager).

1   Go to the TEMPRO website (www.tempro.org.uk) and register your email address.

2   Click the ‘Download Data’ link on left-hand menu bar, which brings up the ‘Download Tempro Data’ page.

3   Click the ‘Download’ button for the TEMPRO system file appropriate for your computer system, and save it in an appropriate folder.

4   Once downloaded, open the containing folder and double click the application file to launch the TEMPRO installation programme. Theses are currently called:

·    “TemproSystem_021107_51.exe” for Windows XP and Vista; or

·    “TemproSystem_060420_50.exe” for previous versions of Windows.

5   Follow onscreen instructions to install the TEMPRO software to the correct location (C:/TEMPRO).

6   Once the programme is installed return to the ‘Download Tempro Data’ page and download the most recent version of the datasets (currently Version 5.4) for the region(s) that you require.  Save these in an appropriate folder.

7   Run the application file (file ending “.exe”) for each region. Unzip your data, saving the values to the “C:/TEMPRO/Data” folder.  This folder will be created automatically during step 5. Once the data are extracted from the file, close the application, and repeat this step for each regional dataset downloaded.

N.B The Tempro Help Documents that are also available to download on the ‘Download Tempro Data’ page (e.g. “TEMPRO Guidance Note”) will provide useful background information should you require it.

8   Open the TEMPRO programme.

9   The front page of TEMPRO has two windows; ‘Datasets Available’ and ‘Chosen Datasets’.  The ‘Datasets Available’ window should contain the downloaded regional dataset(s).  Highlight the dataset required and under the ‘Actions’ tab select ‘Generate Orig/Dest Data’.

NB. You only need to do this once, when using data for a second time, the origin and destination data will still be available.

10 Once the data generation is complete for the desired region(s), TEMPRO is ready to use to derive future traffic growth factors as described above.

11 These results should ONLY be used to weight RTF and NRTF factors, NOT as traffic growth factors in their own right.

(19 February 2009)

The simple answer is that it depends.  Given our current understanding of diffusion tube performance, there are some factors that would encourage the use of local collocation results, and others that would indicate that an average of several studies would be more representative.

The most important factors to be considered when deciding which bias adjustment factor to use are the following:

•  Tube exposure time (1 week, 2 weeks, 1 month)
•  Length of the monitoring study
•  QA/QC of the chemiluminescence analyser
•  QA/QC of diffusion tubes
•  Siting of the co-location study
•  Siting of other tubes in the survey

Local Authorities using diffusion tubes as part of their Review and Assessment are advised to report both the adjustment factor from their local study, and the “national” bias adjustment factor.  However, the decision of which to use will depend upon a number of factors that will need to be considered.  At the end of the day it will be up to each Local Authority to take account of these factors and set out the reasons for the choice made.  Specific factors that should be addressed are:

Cases Where the Locally Obtained Bias Adjustment Factor May be More Representative:

·         Where the diffusion tube exposure periods are weekly or fortnightly (or anything other than monthly – the national database of collocation results only covers monthly exposure.)

·         If the co-location site is unusual in some way: for example, affected by specific large NO_x sources other than road traffic, such as local industrial processes. (This is a strong indication in favour of using a locally-derived factor).

·         For tubes exposed in a similar setting to the co-location site (open/shelter, height…)

·         Where the duration of the whole diffusion tube study is less than one year, especially if it is less than 9 months (when adjustment is best made for a matched time period, rather than using an annual factor).

·         Where the Review and Assessment Helpdesk spreadsheet contains data from few (i.e. less than five) other studies using the same laboratory and preparation technique – although the local result can be added to the national values to derive a new national value (see below).

·         Where the collocation study is spread across more than one calendar year, e.g. October 2003 to September 2004 – especially where there is evidence of different national adjustment factors for different calendar years.

·         For co-location sites with good precision for the diffusion tubes and with high quality chemiluminesence results, i.e. to national AURN standards..

Cases Where the Combined Bias Adjustment Factor May be More Representative:

·         Where the survey consists of tubes exposed over a range of settings, which differ from the co-location site, e.g. the collocation site is in a very exposed setting and the tubes being assessed are on a building façade in a canyon-like street.

·         Where the collocation study is for less than 9 months, although the diffusion tube monitoring is for a longer period.

·         Where the automatic analyser has been operated using local, rather than national, QA/QC procedures.

·         Where data capture from the automatic analyser is less than 90%, or there have been problems with data quality

·         For co-location sites with poor precision.

Bias adjustment factors determined from collocation studies throughout the UK have been collated by the Review & Assessment Helpdesk.  They are available as a spreadsheet and can be found here. If you wish to calculate a new combined adjustment factor by adding your own results to those from all other studies, then please click here.

Further information on the performance of diffusion tubes is available in these recent reports:

·         Air Quality Expert Group: Report on Nitrogen Dioxide in the United Kingdom, April 2004, Appendix 1, available at: http://www.defra.gov.uk/ENVIRONMENT/airquality/publications/nitrogen-dioxide/.

·         Compilation of Diffusion Tube Co-location Studies Carried out by Local Authorities, November 2002, Air Quality Consultants, (available HERE).

·         The Relationship Between Diffusion Tubes Bias and Distance From the Road, July 2006, Air Quality Consultants (available HERE).

These reviews show that the main factor affecting tube performance is the laboratory.  However, there is still residual uncertainty in the bias adjustment factor.  This can be explained to some extent by the influence of the different concentrations to which tubes are exposed and the subsequent chemistry taking place within the tubes, which affects the amount of nitrogen dioxide collected (click here for further information). There is also some evidence from the co-location database that there can be changes in the bias adjustment factors for a particular laboratory over time. This is likely to be due to some unknown change within the laboratory procedures or conditions (including a change of operative or a new source of tubes), as some laboratories have a very consistent bias adjustment factor from one year to another. This means that diffusion tubes should be bias adjusted using the results from collocation studies carried out in the same year.  

Although in many cases, using an overall correction factor derived from as many co-location studies as possible will provide the ‘best estimate’ of the ‘true’ annual mean concentration, it is important to recognise that there will still be uncertainty associated with this bias adjusted annual mean.  One analysis has shown that the uncertainty for tubes bias adjusted in this way is ± 20% (at 95% confidence level). This compares with a typical value of ± 10% for chemiluminesence monitors subject to appropriate QA/QC procedures.

The data used to formulate this calculator are shown in the report NO₂ Concentrations and Distance from Roads, please click here for a full report.  

Wherever possible, authorities are strongly encouraged to use triplicate tube exposures when collocating sites with chemiluminescent analysers, for the determination of local bias adjustment factors.  Where the bias adjustment factor is then used to correct data at sites where only a single tube has been exposed, outliers should not be removed from the triplicate tube data (as this variance is also present in the single tube data).  Where the bias adjustment factor is used to correct data at sites where triplicate tubes have been exposed, then outliers may be removed (defined as being greater than 20% of the Coefficient of Variation)  Full instructions are provided in the ‘Spreadsheet for calculating precision, accuracy and bias adjustment factors of diffusion tubes’.(8 February 2006)

Careful analysis of the results suggests that it is not the distance from the road that matters, but the different concentrations of nitric oxide, nitrogen dioxide and ozone that this reflects. These different concentrations influence the chemistry taking place within the diffusion tube, in particular the formation of additional nitrogen dioxide from a reaction of ozone with nitric oxide.

A relationship has been identified between diffusion tube bias and the measured annual mean nitrogen dioxide concentration that can be used to adjust the diffusion tube result. The effect of this 'tube-chemistry' adjustment depends on the measured concentration: thus a laboratory bias adjusted result of 20mg/m³ would become 18.1mg/m³ after adjustment for bias due to tube chemistry. A value of 40mg/m³ would remain at 40mg/m³ and 60mg/m³ would become 65.1mg/m³. The effect of this adjustment is minimal at concentrations close to the objective of 40mg/m³, thus it will not have a material effect on exceedences of the objective identified using diffusion tubes.

Three broad conclusions arise from this work:

·        Adjusting for tube chemistry reduces the uncertainty of diffusion tube results.  It is not recommended, however, that this adjustment is applied routinely.  There may though be occasions when it is appropriate to apply the tube-chemistry bias adjustment.  For example, it would improve the reliability of the diffusion tube data for use in model verification at both roadside and background sites.

·        The value of a local collocation study (and the subsequent bias adjustment) will be improved if the concentrations being measured are similar to those in the wider survey.  Broadly, this equates to carrying out a collocation study at roadside locations in order to derive a bias adjustment factor to be applied to a survey of roadside concentrations. 

·         Care should be taken to avoid applying a bias adjustment factor derived from a local collocation study carried out for concentrations that are very different to those being measured in the wider survey.  In other words, collocation results from a low concentration site (typically a background site) should not be used to derive a bias adjustment factor for survey results from high concentration sites (typically roadside sites) and vice versa.  There may be circumstances where this is not possible, and this will increase the uncertainty of the results.

What should I do with information on diffusion tube precision?

The attached document shows how to use information from duplicate and triplicate exposure results that distinguishes between Poor and Good diffusion tube precision.  Poor precision can be due to poor handling of the tubes during exposure and/or poor laboratory performance.  The attached document shows precision results for different UK laboratories supplying and analysing diffusion tubes (click here). (29 November 2007)

How do I assess emissions from railway locomotives?

The attached document provides guidance on how to assess emissions from railway locomotives, including a list of rail lines with a heavy traffic of diesel passenger trains and a list of authorities affected (click here). (10 February 2009)

Is the example in Box 2.1 of TG(09) correct?

No.  The example in Box 2.1 has not been updated from the consultation version of the Guidance following a later update of the correction factors.  The addendum below provides the correct figures, though the principle is unchanged, i.e. measured concentration x (projected year factor/measured year factor) = projected concentration.

Addendum to Box 2.1 Example.

The measured NO₂ concentration at a roadside site in Outer London in 2008 is 45.2 µg/m³. The projected concentration for 2010 would be 45.2 x (0.854/0.937) = 41.2 µg/m³. (21 April 2009)

How can I calculate a local bias adjustment factor for nitrogen dioxide diffusion tubes?

A spreadsheet is available to allow calculation of the precision and accuracy (bias) from local collocation studies and can be downloaded here.  Alternatively, the following calculation may be used, particularly in situations where the diffusion tube exposure periods are not monthly or four-weekly (e.g. fortnightly), and do not fit into the spreadsheet provided.

Calculation of Bias Adjustment Factor for Diffusion Tubes

Example

A collocation study produces an annual mean diffusion tube concentration, Dm, of 35 μg/m³ and an annual mean chemiluminesence concentration, Cm, of 39.5 μg/m³.

Bias adjustment

A bias adjustment factor A is calculated as follows:

A = Cm/Dm

For this example A = 39.5/35 = 1.129

The diffusion tube survey annual mean values are then multiplied by this bias adjustment factor.

[A common mistake is to increase the diffusion tube values by the bias, in this example this would be equivalent to multiplying by 1.114 (see below), which is wrong]

Diffusion tube bias B

It is not essential to calculate the diffusion tube bias B, but if required it can be done as follows:

B = (Dm – Cm) / Cm

For this example B = (35–39.5)/39.5 = –4.5/39.5 = –0.114, which is equal to –11.4% – in other words the tubes under-read by 11.4%.

[Bias should always be expressed relative to the chemiluminesence analyser result]

NOTES

1. If there are fewer than 12 months of collocation results, then period means should be calculated for matched periods, i.e. Dm and Cm should cover exactly the same time periods. In addition, data capture for the chemiluminesence monitor should be >90% during each sample period to include this period in the calculation.

2. If a bias adjustment factor is based on a period of less than 9 months, then this factor should not be applied to the results of a 12-month survey.

3. A bias adjustment factor for a short period, e.g. three months can be applied to a survey over the same three months, but remember that an adjustment will also be required to estimate the annual mean (see TG(09) Box 3.2).

4. Bias adjustment factors should be applied to the diffusion tube measurement data to correct for any systematic bias.  Authorities should explicitly state how any bias factors were obtained, and report all original and corrected data.

5. Further guidance on the use of a locally-derived bias adjustment factors as against one from the national database is provided in Box 3.3 in LAQM.TG(09).  (21 April 2009).

The NOx to NO₂ calculator asks me (under “General Inputs” - step 4) to specify the traffic mix. Which option should I choose from the dropdown box?

The dropdown box contains 6 options: “All UK traffic”, “All London traffic”, “All other urban UK traffic”, “All non-urban UK traffic”, “Buses (outside London)”, and “London buses”. The descriptors “urban” and “non-urban” are based upon the DfT’s definition: an urban road is a road within an urban area with a population of 10,000 or more. However, traffic on motorways within urban areas, including London, should be considered separately. It is also recognized that study areas (and roads) which cross more than one area definition are difficult to include. The following is advised:

“All UK traffic” should only be used if none of the other options given below are suitable for your data.

“All London traffic” can be used anywhere in London except adjacent to motorways or where buses dominate the vehicle fleet.

“All other urban UK traffic” is an average of all urban roads outside of London, excluding motorways in urban areas. If your receptors or diffusion tubes are in an urban area and not near to motorways, you can use this option.

“All non-urban UK traffic” gives a national average of traffic on non-urban roads and all motorways. If your receptors or diffusion tubes are outside of urban areas or near to any motorway, even in urban areas, you can use this option.

“Buses (outside London)” can be used outside London where buses dominate your local fleet.

“London buses” can be used inside London where buses dominate your local fleet.

In many situations you may have sufficiently detailed information to calculate your own fNO₂ value. You can do this using the “fNO₂” page of the calculator. As an example, if you are running a dispersion model using traffic data with a detailed fleet composition, you could use the following procedure to generate an emission-weighted fNO₂:

1) run the dispersion model (to predict road-NOx) for each vehicle class independently;

2) calculate the percentage contribution of each vehicle class to total road-NOx at each receptor;

3) note down the fNO₂ values for each vehicle class from the fNO₂ page of the calculator;

4) calculate a weighted average fNO₂ value using the results from steps 2 and 3;

5) enter this value directly into the “NOx to NO₂ sheet” or “Diffusion tubes” sheet.

When you enter your fNO₂ values directly into the calculator, you do not need to specify a traffic mix in under “General Inputs”.   (4 June 2009).

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Common omissions from reports include:

• Failing to consider sources in neighbouring authorities;
• Failing to clearly distinguish between the assessment of junctions, busy roads, new roads etc. (the appraisers cannot assume that junctions etc. have been considered if this is not stated);
• Failing to provide sufficient evidence on the use of the DMRB model (particularly regarding the location of relevant receptors in relation to the point modelled);
• Failing to state that bus stations, ports/shipping or railway locomotives have been considered.

·         The consideration of the appropriate objective(s);

·         The use of appropriate emissions data;

·         The use of a validated, and in most cases a verified model;

·         Predictions at locations relevant for the air quality objective(s) in question. (19 February 2003)

6

(A) LAQM Reports (Updating and Screening Assessments, Progress Reports, AQAP Progress Reports and associated correspondence) submitted via the Report Submission Website

Upon uploading a report on the Report Submission Website the local authority will receive confirmation stating that the report has been submitted and has been received by the relevant Appraisal Team.  Review and Assessment reports (these include Updating and Screening Assessments, Progress Reports and associated correspondence) are sent to UWE/AQC.  Action Plan Progress Reports and associated correspondence are sent to AEA.  If an appraisal response or contact from the relevant Appraisal Team has not been received within the specified time scale (or indeed at any stage within the appraisal period), the local authority may contact Defra and the Devolved Administrations (or the relevant Appraisal Team) for a progress update.

 Figure 1 outlines the steps and timescales involved in both the Review and Assessment and Air Quality Action Plan Progress Report appraisal processes for local authorities using the Report Submission Website.

(B) LAQM Reports (Review and Assessment Reports and AQAP Reports and associated correspondence) submitted as hardcopy or via email to Defra and the Devolved Administrations.

Upon the receipt of a report from a local authority, Defra and the Devolved Administrations[1] send the point of contact within the local authority (the local authority is responsible for ensuring that their contact details are up to date) an email stating that the report has been received and has been forwarded to the relevant Appraisal Team.  Review and Assessment reports (these include Updating and Screening Assessments, Detailed Assessments, Progress Reports, Further Assessments and associated correspondence) are sent to UWE/AQC.  Air Quality Action Plans, Action Plan Progress Reports and associated correspondence are sent to AEA.  If an appraisal response or contact from the relevant Appraisal Team has not been received within the specified time scale (or indeed at any stage within the appraisal period), the local authority may contact Defra and the Devolved Administrations (or the relevant Appraisal Team) for a progress update.

Figure 2 outlines the steps and timescales involved in both the Review and Assessment and Air Quality Action Plan appraisal processes for local authorities submitting reports as hard-copy or via email to Defra and the Devolved Administrations.

Table 1 outlines the timescales for Review and Assessment (taken from Policy Guidance LAQM.PG(09)).

Appraisal Contact Details

For Review and Assessment Reports contact the Review and Assessment Helpdesk:

Tel: 0117 32 83668

Email: aqm-review@uwe.ac.uk

For Air Quality Action Plan and Action Plan Progress Reports contact the Air Quality Action Plan Helpdesk

Tel: 0870 190 6050

Email: lasupport@aeat.co.uk.

[1] London authorities also need to send reports to the GLA Air Quality Team who will respond on behalf of the Mayor of London.  The GLA Air Quality Team review AQAPs and AQAP Progress Reports in house, including comments for other bodies in the GLA Group (e.g. TfL) where relevant.  Review and Assessment reports are appraised on behalf of the GLA by UWE/AQC.  The GLA will respond to all reports within 8 weeks of receipt.

The column in the Table is to cover the advice set out in LAQM.TG(09), Para 3.11 which states “if the conclusions of the Review and Assessment are to be based solely on the use of monitoring data, then it will be critical to ensure that these sampling locations take into account those places where concentrations are expected to be the highest, and where the public may be exposed over the relevant averaging period of the objectives.”  i.e. to ensure that if reliance is placed solely upon monitoring data to determine that there are no exceedences of the air quality objectives, then appropriate consideration is given to all relevant locations where pollution concentrations are reasonably expected to be the highest.

As an example, a nitrogen dioxide diffusion tube site recorded an annual mean concentration of 38.5 µg/m³ in 2008.  If this result were used to conclude that there are no exceedences of the objective within the study area, the local authority needs to be confident that concentrations are not likely to be higher at other locations where monitoring has not been carried out, e.g. at properties closer to a road or junction.  The ‘study area’ might be a whole town, a section of a town, or an individual road link, i.e. the area that would potentially be considered within a discrete Detailed Assessment.

Therefore, to complete the column, you should indicate which (if any) monitoring sites are at worst-case locations for a particular study area.  There is no need to complete this column for all monitoring sites, and it does not apply to background sites.  When considering whether monitoring represents ‘worst case’, issues such as proximity to junctions, proximity of exposure to the carriageway, levels of congestion, street canyons etc. should be taken into account.

If worst-case locations have not been included in the survey and concentrations are close to the objective, then it will be necessary to supplement the monitoring data with an appropriate modelling study, such as a verified DMRB assessment, to identify the concentration at the worst-case location.  The fall-off with distance calculator tool could also be used where appropriate (see Box 2.3 in TG(09)).  (21 April 2009).

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