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4. environmental assessment (continued)
4. Environmental Assessment (continued)
4.3 Air Quality and Greenhouse Gases
4.3.1 Introduction
This section details the Stage 2 air quality assessment for the Alternative Proposal for the proposed A14 improvements between Ellington and Fen Ditton, Cambridgeshire.
Vehicle exhausts contain a number of pollutants including carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons, oxides of nitrogen (NOx) and particles. The quantity of each pollutant emitted depends upon the type and quantity of fuel used, engine size, speed of the vehicle and abatement equipment fitted. Once emitted, the pollutants disperse in the air. Pollutant concentrations in the air can be measured or modelled and then compared with ambient air quality criteria.
4.3.2 Air Quality Criteria and Pollutants
Air quality criteria can be readily divided into two groups; those that are mandatory and those that are designed for guidance. Mandatory criteria that apply to the UK are the objectives from the Air Quality Strategy (AQS) for the UK and the European Community Directive limit values, which are incorporated into Regulations. The air quality criteria used in this assessment are given in the following table.
| Pollutant | Criteria | Date to be Achieved by | Objective |
|---|---|---|---|
| NO2 | Annual Mean | 2005 | 40 |
| NO2 | Hourly mean | 2005 | 18 exceedances |
| PM10 | Annual Mean | 2004 | 40 |
| PM10 | 24-Hour Mean | 2004 | 35 exceedances |
| PM10 | Annual Mean (provisional) | 2010 | 20 |
| PM10 | 24-Hour Mean (provisional) | 2010 | 7 exceedances |
| CO | Maximum daily 8-hour running mean | 2003 | 10 |
| Benzene | Running Annual Mean | 2003 | 16.25 |
| Benzene | Running Annual Mean | 2010 | 5 |
| 1,3 butadiene | Running Annual Mean | 2001 | 2.25 |
It should be noted that whilst the current annual mean AQS objective for PM10 is 40µg/m3, with 35 exceedances of the 24-hour mean AQS objective, a more stringent objective of 20µg/m3, with 7 exceedances of the 24-hour mean is to be applied in 2010, although currently these objectives are provisional and not included in Regulations.
AIR POLLUTANTS
POLLUTANTS Nitrogen Dioxide (NO2)
Nitrogen dioxide is a secondary pollutant produced by the oxidation of nitric oxide (NO). Nitric oxide and nitrogen dioxide are collectively termed nitrogen oxides (NOx). Approximately half of the UK NOx emissions are from road transport. The majority of NOx emitted from vehicles is in the form of nitric oxide, which oxidises rapidly in the presence of ozone to form nitrogen dioxide. In high concentrations, nitrogen dioxide can affect the respiratory system.
Particulate Matter
Particulate matter in vehicle exhaust gases consists of carbon nuclei onto which a wide range of compounds are absorbed. These particles are less than 10 µm in diameter. Particles with a median diameter of less than 10 µm are referred to as PM10. Diesel engines produce the majority of particulate emissions from the vehicle fleet. About a quarter of primary PM10 emissions in the UK are derived from road transport. Particulate matter appears to be associated with a range of symptoms of ill health including effects on the respiratory and cardiovascular systems, on asthma and on mortality.
Carbon Monoxide (CO)
The majority of carbon monoxide emitted in the UK is from motor vehicles. It is readily absorbed through the lungs and reduces the oxygen carrying capability of the blood.
Hydrocarbons
The term 'hydrocarbons' is used to include all organic compounds emitted from vehicles both in the exhaust and by evaporation from the fuel system, and covers many hundreds of different compounds. About one third of the UK hydrocarbon emissions are produced by road transport. Hydrocarbons are important precursors of photochemical smog and oxidising compounds. The DMRB requires an assessment for benzene and 1, 3-butadiene as these are included in the Air Quality Strategy. They are both genotoxic carcinogens and exposure to them is associated with certain types of leukaemia.
Carbon Dioxide
Carbon dioxide is a major product of the combustion of carbon containing materials. Carbon dioxide does not affect human health at ambient levels and so is not significant as a local pollutant but is important for its national and international role in climate change. About 20% of the UK carbon dioxide emissions are produced by road transport.
4.3.3 Existing Conditions
LOCAL AIR QUALITY REVIEW AND ASSESSMENT
All local authorities are required by Part IV of the Environment Act 1995 to review air quality in their area and to assess present and likely future air quality against set objectives.
If an area is identified as being unlikely to achieve the Air Quality Strategy (AQS) objectives, the local authority is required to designate an Air Quality Management Area (AQMA) and develop an action plan to improve air quality.
The following local authorities contain roads with a significant change in traffic (±10%) with the proposed improvements and/or a section of the existing or new alignment of the A14:
- Cambridge City Council
- Huntingdonshire District Council
- South Cambridge District Council
Air quality review and assessment is a rolling process which requires periodic updating due to the changing nature of the air quality with time. A partnership of five local authorities in and around Cambridgeshire, including those listed above, was set up to carry out the review and assessment of air quality in Cambridgeshire. Following the completion of the first round of the review and assessment process none of the local authorities above have declared any AQMAs.
As part of the second round of the review and assessment process local authorities must complete an updating and screening assessment (USA) to identify matters that have changed since the first round of review and assessment and identify sources that may lead to an air quality objective being exceeded. A detailed assessment is required where there is a possibility of AQS objectives being exceeded.
As part of the second round of the review and assessment process local authorities must complete an updating and screening assessment (USA) to identify matters that have changed since the first round of review and assessment and identify sources that may lead to an air quality objective being exceeded. A detailed assessment is required where there is a possibility of AQS objectives being exceeded.
Monitoring
Measurements of pollutant concentrations may be made by deploying analytical instruments that measure continuously and record the average concentrations over specified time intervals. Simpler sampling devices, such as diffusion tubes, adsorb pollutants over a longer time period and are subsequently analysed at a laboratory to give an average concentration for the sampling period. National survey results from both types of monitoring are published in the UK National Air Quality Information Archive1, and the closest relevant data are summarised below.
Continuous Monitoring
Defra operates a network of automated continuous monitoring sites throughout the UK. The closest sites in the network to the study area are Cambridge Roadside, Norwich Centre and Wicken Fen. Descriptions of these sites are given below, together with their location in relation to the study area.
- Cambridge Roadside is a roadside site in the centre of Cambridge, located approximately 4 km south of the A14. The monitor is located at first floor level at a height of approximately 4 metres and a distance of 2.5 metres from the kerbside of a busy urban road leading traffic directly to the city centre shopping area. Nitrogen oxides have been monitored since 1999. This site is located at grid reference 545300 258300.
- Norwich Centre is an urban centre site located approximately 90km north east of the A14. The nearest road to the site is located approximately 12 metres away, although traffic flow is free flowing and very light (1 or 2 vehicles per minute observed off peak). O3, PM10, NOx and SO2 have been monitored since 1997 and benzene since 2002. This site is located at grid reference 623000 308900. Although located at some distance from the A14 this site was selected as it is the closest Defra site where PM10 and CO are monitored.
- Wicken Fen is a rural site located approximately 12km north east of the A14. The area surrounding the monitoring station is open field with isolated trees. O3, NO2 and SO2 have been monitored between 1997 and 2002. This site is located at grid reference 556400 269200
Continuous monitoring is also undertaken by local authorities at locations given in the following table.
| Site | Local Authority | Grid Reference | Site Type | Pollutants | Proximity to A14 | Available Results |
|---|---|---|---|---|---|---|
| Parker Street | Cambridge City Council | 545366 258391 | Roadside | NO2, PM10 | 4km South of Girton Junction | 2000-2004 |
| Silver Street | Cambridge City Council | 544758 258118 | Roadside | NO2, PM10 | 4km South of Girton Junction | 2000-2004 |
| Gonville Place | Cambridge City Council | 545508 257828 | Roadside | NO2, PM10 | 4km South of Girton Junction | 2000-2004 |
| Regent Street | Cambridge City Council | 545287 258124 | Roadside | NO2, CO | 4km South of Girton Junction | 2000-2004 |
| Newmarket Road | Cambridge City Council | 546312 258896 | Roadside | NO2, PM10 | 4km South of Girton Junction | 2002 |
| Huntingdon Ring Road | Huntingdon-shire DC | 524056 271533 | Roadside | NO2, PM10 | 120m North of A14 at Huntingdon | 2000-2004 |
| Godmanchester | Huntingdon-shire DC | 524419 271312 | Roadside | NO2, PM10 | 25m North of A14 at Godmanchester | 2002-2004 |
| Bar Hill | South Cambridge-shire DC | 538650 263750 | Roadside | NO2, PM10 | On eastbound A14 Carriageway at Bar Hill | 2001-2003 |
| Impington | South Cambridge-shire DC | 543850 261750 | Roadside | NO2, PM10 | On westbound Carriageway of A14 at Impington | 2002-2003 |
Non-continuous Monitoring
Nitrogen dioxide can also be monitored passively using diffusion tubes. Local authorities across the UK take part in Defra's nitrogen dioxide survey and also carry out their own monitoring surveys.
Data from the following Defra sites are considered here:
- Cambridge - 5 sites located approximately 3-4 km south of the A14 at Histon Junction;
- Histon - 5 sites located approximately 2 km north of the A14 at Histon Junction;
- Sawston - 2 sites located approximately 3 km east of the M11 between junctions 10 and 11/ 12km south of the A14 at Fen Ditton;
- St Neots - 5 sites located approximately 12 km south southeast of the A14 at Huntingdon.
Local authorities monitor NO2 with diffusion tubes at the following number of locations:
- Cambridge City Council - 42 locations;
- Huntingdonshire District Council - 22 locations;
- South Cambridgeshire District Council - 19 locations.
Full results from the monitoring locations described above are presented in the Environmental Assessment Report Addendum, but summarised below.
Monitoring Survey near A14
Atkins commenced in a year long nitrogen dioxide monitoring programme using diffusion tubes in June 2004. Nineteen sites were selected, based on the expected changes in traffic flows on the road network in the study area. The Environmental Assessment Report and Addendum give details of the location of sites.
As recommended by Defra's Technical Guidance3 three diffusion tubes were co-located with a continuous monitor (Cambridge Roadside site) to enable the accuracy and precision of the tubes to be determined. Comparison of the mean concentrations in each monitoring period gives a correction factor which can then be applied to the diffusion tubes at the other sites. The corrected results for the first seven months of monitoring are shown in the following table.
Concentrations are shown to exceed the annual mean AQS objective at sites 12, 13 and 14, the Trinity Foot Public House and 5m and 10m from the edge of the A14 in transect respectively. Concentrations at all other sites were below the AQS objective, although marginally so at the Bar Hill monitor and Cambridge Roadside monitor. A report will be issued following completion of the monitoring survey.
SUMMARY
Concentrations of 1,3-butadiene, benzene and carbon monoxide are expected to achieve their respective AQS objectives throughout the study area. There are numerous exceedences of the annual mean NO2 objective, especially at roadside sites, indicating that concentrations are likely to be sensitive to any changes in traffic flows. The hourly NO2 objective was exceeded at one site close to the A14 in 2003. The annual mean PM10 AQS objective was achieved, but the 24-hour objective was exceeded at two sites close to the A14 in 2003.
2 (Ref: Local Air Quality Management: Technical Guidance LAQM.TG(03), Defra, 2003)
Table 4.8 - Bias Adjusted Nitrogen Dioxide Monitoring Results (µg/m3)
4.3.4 Methodology
APPROACH TO ASSESSMENT
The assessment was carried out in accordance with the Design Manual for Roads and Bridges (DMRB) Volume 11 section 3, part 1, air quality, revision February 2003 and Transport Analysis Guidance (TAG) The Local Air Quality Sub-objective Unit 3.3.3, February 2004. The scheme has been assessed in terms of
- A constraints map showing areas within 200m of roads affected by the scheme, which may experience changes in air quality;
- A Local Impact Assessment comprising estimated pollutant concentrations at selected properties in relation to the relevant criteria;
- An assessment of the overall change in exposure to concentrations of NO2 and PM10 following guidance in the DfT's TAG, the TAG Assessment
CONSTRAINTS MAP
A constraints map was drawn to show areas within 200m of the roads affected by the proposed improvements that are likely to have a change in air quality. This allows identification of the number of properties where people are likely to be subjected to a change in air quality, the identification of sensitive properties and properties likely to experience higher than average pollutant concentrations at locations such as road junctions. Sensitive properties include those where there may be vulnerable occupants, such as schools, hospitals or homes for the elderly. The following table displays the type and number of sensitive properties identified within 200m of the A14 and affected roads.
| Type of Sensitive Receptor | Number within 200m of A14 and Affected Roads |
|---|---|
| Care Home | 1 |
| Clinic | 7 |
| Hospice | 2 |
| Hospital | 5 |
| School | 60 |
| Surgery | 29 |
LOCAL AIR QUALITY IMPACT ASSESSMENT
The DMRB states that the screening method should be used to estimate concentrations of carbon monoxide, nitrogen dioxide, benzene, 1,3-butadiene and particulate matter (PM10) to compare with AQS objectives. However, the assessment focuses in particular on the pollutants NO2 and PM10 as the air quality criteria for these two pollutants are likely to be most difficult to achieve in the vicinity of roads. Predictions were made both with and without the proposed A14 improvements, termed the scheme and do-minimum respectively. The years selected for assessment were the existing case (2003), and the opening year (2010).
4.3.5 Alternative Proposal
The assessment was carried out for the Alternative Proposal (a limited junction option) and a Do Minimum.
The study area for the air quality assessment has been defined based on the change in traffic on the road network. Additional traffic is expected to be induced on the off-line section of the A14 and the pattern of traffic flow on the road network will be affected by the increased capacity of this road.
A large number of road links are within the study area. DfT's TAG states "options which change traffic flows by less than 10% can usually be scoped out, unless the road is a motorway or there are particular sensitivities". On this basis the network for the air quality assessment included all existing and new alignments of the A14, and all other roads with flows of greater than 5,000 vehicles per day which experience an increase or decrease in traffic of greater than 10% with any of the traffic options.
The road network assessed for the study area is illustrated in the air quality constraints map.
Receptor Selection
Usually, a number of specific properties or receptors are chosen for assessment. However, for this assessment, as the study area under consideration was so large, Ordnance Survey Address-Point® data was used to pinpoint the location of residential properties. For each property, the Address-Point® dataset contains a unique identifier, national grid reference and postal address. When identifying properties from maps without address point data, accidental consideration of structures not used for occupancy by people can occur. Using Address-Point® data ensures only buildings with a postal address are included in the count. The data also contains a field for business name which is used to screen the data to remove business addresses.
The use of an access database enabled the pollutant concentrations at all properties within 200m of the scheme and affected roads to be calculated. In addition to residential properties, the effect on air quality at schools and other sensitive properties within 200m of affected roads can be assessed. Concentrations at properties near the junctions on the A14 were calculated using the DMRB spreadsheet rather than the database, due to the complexity of the junctions.
Comparison of Modelled and Monitored Concentrations
To provide some validation of the concentrations predicted using the DMRB, a comparison of estimated and measured concentrations was undertaken for NO2 and PM10 at the location of continuous monitoring stations close to the A14.
The DMRB screening method was used to calculate concentrations at the local authority continuous monitoring sites at Bar Hill, Godmanchester and Impington.
In addition, the DMRB screening method was used to calculate concentrations at the locations of the nitrogen dioxide diffusion tube survey being carried out by Atkins. Data from the first seven months of the survey, adjusted for bias, was used to compare with the estimated results.
TAG Assessment
This assessment gives a quantitative indication of whether the scheme would lead to an overall improvement or deterioration in air quality at properties and is based on the DfT's Transport Analysis Guidance (TAG) The Local Air Quality Sub-Objective Unit 3.3.1, February 2004.
This assessment gives a quantitative indication of whether the scheme would lead to an overall improvement or deterioration in air quality at properties and is based on the DfT's Transport Analysis Guidance (TAG) The Local Air Quality Sub-Objective Unit 3.3.1, February 2004.
Pollutant concentrations decrease with increasing distance from the traffic, therefore concentrations are calculated at 20 m, 70 m, 115 m and 175 m from the road centre, with and without the proposed scheme, for each route option.
The number of properties in 50 m bands from the centre of each road link was counted out to a distance of 200 m for the do minimum and scheme scenarios. The Address-Point® dataset, described above, and a geographic information system was used to facilitate this. The number of properties in each band is multiplied by the concentration calculated for that band for the do minimum and scheme scenarios. This is carried out for each of the four bands and the results added together to give a total for each scenario. The do-minimum value is deducted from the scheme value for each affected route. The overall assessment score is calculated by summing values over all routes, with an improvement (decrease in concentrations) having a negative value and a deterioration (increase in concentrations) having a positive value.
RESULTS
Local Air Quality Impact Assessment
Pollutant concentrations at properties within 200m of the existing and new alignments of A14 and other roads affected by a significant change in traffic due to the scheme have been calculated. This area includes some 65,000 properties.
Due to the large number of properties assessed, it has not been possible to report the predicted concentrations at each. Instead, the concentrations have been compared with the AQS objectives to determine whether any exceedances have been predicted and the magnitude of any changes in concentrations analysed.
Exceedances of AQS Objectives
In 2010 the AQS objectives for all pollutants are expected to be achieved at all receptors with the Alternative Proposal. Some exceedances of the provisional 2010 annual mean PM10 objective were predicted in Cambridge. Approximately 28 properties are expected to exceed this provisional objective with the Do-Minimum, and 21 properties with the Alternative Proposal.
Changes in Concentrations at Receptors
The following tables give details of the maximum concentrations and greatest changes predicted at receptors for NO2 and PM10 respectively.
| Traffic Option | Maximum Conc. | Greatest Increase | NO2 (µg/m3) Traffic Option Maximum Conc. Greatest Increase No Properties with Change >4 | Greatest Decrease | No Properties with Change <-4 |
|---|---|---|---|---|---|
| BASE | 42 | ||||
| Do Minimum | 33 | ||||
| Alternative Proposal | 31 | 7.84 | 4 | -8.72 | 27 |
| Traffic Option | Maximum Conc. | Greatest Increase | NO2 (µg/m3) Traffic Option Maximum Conc. Greatest Increase No Properties with Change >2 | Greatest Decrease | No Properties with Change <-2 |
|---|---|---|---|---|---|
| BASE | 30 | ||||
| Do Minimum | 22 | ||||
| Alternative Proposal | 21 | 2.28 | 1 | -3.15 | 2 |
There are expected to be both increases and decreases in concentrations at receptors with the scheme.
With the Alternative Proposal there are 4 properties with an increase in annual mean NO2 concentrations of greater than 4µg/m3, and 27 properties with a decrease in annual mean NO2 concentrations of greater than 4µg/m3. The greatest increase for NO2 with the scheme is 8µg/m3, and the greatest decrease is 9µg/m3.
For PM10 there is 1 property with an increase in annual mean concentrations greater than 2µg/m3 and 2 properties expected to have a decrease in annual mean PM10 concentrations of greater than 2µg/m3 . The greatest increase for PM10 is 2µg/m3, and the greatest decrease with the scheme is 3µg/m3.
Junction Options
Annual mean concentrations of NO2 and PM10 at 14 receptors near junctions on the proposed and existing alignments of the A14 for the alternative proposal are shown in the Environmental Assessment Report Addendum.
None of the concentrations predicted at the receptors are expected to exceed any of the AQS objectives in 2010 with or without the scheme. The majority of receptors are expected to have similar concentrations with both scheme options, the one exception being Hackers Fruit Farm, where concentrations differ due to the traffic flows associated with the proposed local access road.
For NO2 the greatest increase at any receptor is 6.3 µg/m3 at Little Cottage, as the proposed route passes close to this receptor.
Concentrations at Grafham Road Cottages, Depden Farm, Rectory Farm, Tree Avenue and Impington Farm are expected to have increases of 4.8, 4.1, 4.0, 4.0 and 3.4 µg/m3 respectively. Increases at all other receptors are expected to be less than 3 µg/m3.
The greatest decreases with the scheme proposal are expected to occur at the 8 additional receptors affected by the Alternative Proposal between Ellington and Fenstanton. These include a decrease of 13.1 µg/m3 for 28 Greendale, 10.4 µg/m3 for Rectory Farm near Godmanchester Junction, 10.3 µg/m3 for 52 Cambridge Villas and 9.2 µg/m3 for the Motel at Fenstanton. At the other receptors (Meadow View Farm, 17 Lodge Close, 9 Laurel Court and 51 Pitfield Close) concentrations are expected to decrease by 3-4 µg/m3.
The changes in concentrations for PM10 follow the same pattern as for NO2. The greatest increases for PM10 are at Little Cottage, Depden Farm, and Tree Avenue with increases of 2.1, 1.3, and 1.1 µg/m3 respectively. The greatest decreases are expected to occur at the receptors affected by the Alternative Proposal between Ellington and Fenstanton. Decreases range between 1.1 and 7.4 µg/m3. All other receptors are expected to have a negligible change.
Generally the concentrations predicted for the Alternative Proposal options are slightly higher than those for the CHUMMS Strategy orange route options at all receptors; with concentrations up to 5 µg/m3 higher for nitrogen dioxide, and 2 µg/m3 higher for PM10.
4.3.6 Comparison of Modelled and Monitored Concentrations
CONTINUOUS MONITORING SITES
The results of the comparison of modelled and monitored concentrations for 2003 are shown in the following table.
| Site | Source Roads | Pollutant | Predicted Annual Mean | Measured Annual Mean | Difference (%) | Difference (µg/m3) |
|---|---|---|---|---|---|---|
| Bar Hill | A14 | NO2 | 37 | 50 | 26 | 13 |
| PM10 | 23 | 33 | 30 | 10 | ||
| God-manchester | A14, B1044 | NO2 | 38 | 40 | 5 | 2 |
| PM10 | 24 | 29 | 17 | 5 | ||
| Impington | A14 | NO2 | 35 | 52 | 33 | 17 |
| PM10 | 22 | 39 | 44 | 17 |
The results indicated that at Bar Hill and Impington there was an under prediction in modelled concentrations of NO2 and PM10 compared to the measured concentrations of around 30%. Average factors of 1.3 and 1.5 for NO2 and PM10 respectively, were derived. Meteorological conditions in 2003 were largely responsible for poorer air quality in this year than in previous years, hence concentrations were also estimated for 2002 using the 2003 traffic data, and compared with the monitoring data for 2002, shown in the following table.
| Site | Source Roads | Pollutant | Predicted Annual Mean | Measured Annual Mean | Difference (%) | Difference (µg/m3) |
|---|---|---|---|---|---|---|
| Bar Hill | A14 | NO2 | 38 | 42 | 9 | 4 |
| PM10 | 23 | 30 | 22 | 07 | ||
| God-manchester | A14, B1044 | NO2 | 39 | 39 | 0 | 0 |
| PM10 | 24 | 20 | -22 | -4 | ||
| Impington | A14 | NO2 | 36 | 53 | 32 | 17 |
| PM10 | 22 | 30 | 26 | 8 |
In 2002 there is still an under prediction in modelled concentrations of NO2 and PM10 compared to the measured concentrations. However, at Godmanchester the modelled concentrations are more comparable. At Impington there is still an under prediction of around 30%, and at Bar Hill the under prediction is around 15-20%. Average factors of 1.2 and 1.1 for NO2 and PM10 respectively, were derived.
When receptor concentrations in 2010 are multiplied by these factors there will still be no exceedances of annual mean AQS objective for either NO2 or PM10. However, with the 2003 adjustment factors, concentrations of NO2 may exceed the annual mean AQS objective at a small number of receptors with the Do Minimum. The majority of these receptors are located in Cambridge. However, there are some receptors located in the vanity of the A14 which are expected to exceed the objective with the Do Minimum. These receptors are given in the following table.
| Traffic Option | Properties |
|---|---|
| Do Minimum | Crouchfield Villa, Hackers Fruit Farm, Huntingdon Road & Cambridge Road, Orthwaite, Huntingdon. |
| Alternative Proposal |
Diffusion Tube Survey
Nitrogen dioxide results estimated using the DMRB have also been compared with the monitoring data from the diffusion tube survey carried out by Atkins. The results of the comparison are presented in the following table.
| Site No | Location | Modelled Concentration | Monitored Concentration | Difference µg/m3 | % Under/ Over Estimation |
|---|---|---|---|---|---|
| 1,2,3 | Cambridge Continuous monitor | 29.8 | 37.2 | -7.4 | -24.8% |
| 4 | Impington Continuous monitor | 38.6 | 25.5* | 13.2 | 34.1% |
| 5 | Brampton Lodge | 22.1 | 18.0 | 4.1 | 18.4% |
| 6 | Thrapston Road, Brampton | 33.9 | 27.1 | 6.8 | 20.1% |
| 7 | Depden Farm | 20.2 | 17.5 | 2.8 | 13.6% |
| 8 | Castle Hills, Huntingdon | 28.9 | 27.9 | 1.0 | 3.5% |
| 9 | Cambridge Villas, Godmanchester | 33.1 | 25.2 | 7.9 | 23.7% |
| 10 | Rectory Farm | 36.9 | 28.9 | 8.0 | 21.6% |
| 11 | Gore Tree Farm | 29.2 | 28.2 | 1.1 | 3.6% |
| 12 | Trinity Foot PH | 35.8 | 44.7 | -8.8 | -24.6% |
| 13 | Transect 5m | 35.9 | 55.8 | -19.9 | -55.4% |
| 14 | Transect 10m | 34.3 | 49.1 | 14.8 | -43.0% |
| 15 | Transect 50m | 26.4 | 35.0 | -8.7 | -32.9% |
| 16 | Transect 130m | 21.1 | 26.2 | -5.1 | -23.9% |
| 17 | Acorn Ave, Bar Hill | 22.0 | 27.4 | -5.4 | -24.3% |
| 18 | Bar Hill monitor | 34.6 | 39.3* | -4.7 | -13.6% |
| 19 | Cambridge Road, Girton | 31.8 | 20.8 | 11.0 | 34.7% |
The results show that there is an overall variation of +35% and -50% between the concentrations modelled and monitored. At two rural locations, where there are no road sources within 200m (Brampton Lodge and Depden Farm the background concentrations taken from the 1km grid squares which are provided in the Air Quality Archive were higher than those measured using diffusion tubes (22µg/m3 and 20µg/m3 compared to 18µg/m3 and 18µg/m3 respectively). This suggests that at rural locations, the DMRB method may be overestimating by up to 20% due to background concentrations used. However, as the concentrations at these sites are well below the AQS objective, this is unlikely to have any significant consequences.
At the other extreme, concentrations are being under estimated by the DMRB by up to 55% at the closest points to the A14, 5 and 10m from the edge of the carriageway. It is not certain why this underestimation is occurring; it may be as a result of the prevailing wind direction which the DMRB does not take into account. At other locations, estimated concentrations are within ±35% of the measured data (which can be considered a reasonable estimate). Overall, the model was found to be under estimating by around 5%.
4.3.7 TAG Assessment Results
The results of the TAG assessment are summarised in the following table.
The assessment of the Alternative Proposal shows that there is an overall increase in PM10 and NO2 concentrations at the properties near the off-line section of the A14. In the wider network, there is expected to be a large decrease overall in both PM10 and NO2 concentrations, which outweighs the increase near the off-line section.
The overall assessment shows that the scheme will lead to an improvement in both PM10 and NO2 concentrations at affected properties compared to the Do Minimum.
| Pollutant | PM10 Assessment | No. Properties with Improvement | No. Properties with No Change | No. Properties with Deterioration |
|---|---|---|---|---|
| PM10 | -950 | 18,982 | 0 | 2,122 |
| NO2 | -3,442 | 18,846 | 0 | 2,258 |
4.3.8 Comparison of the Alternative Proposals with the CHUMMS Strategy
CHANGES IN CONCENTRATIONS
The following two tables compare the maximum concentrations and greatest changes predicted at receptors for NO2 and PM10 respectively, for the CHUMMS Strategy and Alternative Proposal.
The maximum predicted concentrations of NO2 and PM10 are the same for both the Alternative Proposal and the CHUMMS Strategy. Fewer properties are expected to experience a change in NO2 concentrations of greater than ±4 µg/m3 for the Alternative Proposal. Similarly for PM10 there are expected to be fewer properties expected to experience a change in concentrations of greater than ±2 µg/m3 for the Alternative Proposal.
With the CHUMMS Strategy, the largest decrease in concentrations is significantly greater for both pollutants than with the Alternative Proposal. This is a result of the improvements along the Huntingdon Viaduct section.
| Traffic Option | Maximum Conc. | Greatest Increase | No Properties with Change >4 | Greatest Decrease | No Properties with Change <-4 |
|---|---|---|---|---|---|
| CHUMMS Strategy | 31 | 5.4 | 69 | -15.5 | 95 |
| Alternative Proposal | 31 | 7.84 | 4 | -8.72 | 27 |
| Traffic Option | Maximum Conc. | Greatest Increase | No Properties with Change >2 | Greatest Decrease | No Properties with Change <-2 |
|---|---|---|---|---|---|
| CHUMMS Strategy | 21 | <2 | 0 | -6.2 | 37 |
| Alternative Proposal | 21 | 2.28 | 1 | -3.15 | 2 |
The following two tables compare the changes in concentrations at 20m (taken from the TAG assessment) between the CHUMMS Strategy and Alternative Proposal through the Huntingdon Viaduct and along the New A14 alignment, south of Godmanchester, the key areas where there are differences between the options.
The following two tables compare the changes in concentrations at 20m (taken from the TAG assessment) between the CHUMMS Strategy and Alternative Proposal through the Huntingdon Viaduct and along the New A14 alignment, south of Godmanchester, the key areas where there are differences between the options.
| Pollutant | CHUMMS Strategy | Alternative Proposal | Difference |
|---|---|---|---|
| NO2 | -6.4 | -3.5 | 2.9 |
| PM10 | -2.7 | -0.8 | 1.9 |
| Pollutant | CHUMMS Strategy | Alternative Proposal | Difference |
|---|---|---|---|
| NO2 | 13.0 | 12.1 | -0.9 |
| PM10 | 4.8 | 4.0 | -0.8 |
TAG ASSESSMENT
A comparison of the results for the Alternative Proposal with the CHUMMS Strategy previously assessed was made. A comparison of the TAG assessment scores are given in the following two tables.
| Option | PM10 Assessment | No. Properties with Improvement | No. Properties with No Change | No. Properties with Deterioration |
|---|---|---|---|---|
| CHUMMS Strategy | -525 | 20,665 | 0 | 9,041 |
| Alternative Proposal | -950 | 18,982 | 0 | 2,122 |
| Option | PM10 Assessment | No. Properties with Improvement | No. Properties with No Change | No. Properties with Deterioration |
|---|---|---|---|---|
| CHUMMS Strategy | -1,731 | 19,528 | 0 | 10,178 |
| Alternative Proposal | -3,442 | 18,846 | 0 | 2,258 |
The CHUMMS Strategy is expected to result in a greater improvement on the existing road network than the Alternative Proposal. However the Alternative proposal will have a much smaller deterioration in air quality at properties in the vicinity of the new A14 route alignments than the CHUMMS Strategy. The overall assessment scores indicate that the Alternative Proposal is expected to result in a greater improvement in air quality than the CHUMMS Strategy.
The total number of properties affected is expected to be smaller for the Alternative Proposal. The Alternative proposal will result in a similar number of properties having an improvement in air quality, but there will a lot fewer properties with a deterioration in air quality than for the CHUMMS Strategy.
4.3.9 Conclusions
The Stage 2 air quality assessment has consisted of examining existing conditions, assessing the change in concentrations at properties likely to be affected by the proposed scheme options, and undertaking an overall assessment of exposure according to the TAG methodology.
Measured concentrations of annual mean nitrogen dioxide are expected to exceed the AQS objective near roadside sites in the study area, as well as near the A14. Concentrations of PM10 also exceeded the 24-hour mean objective at sites near the A14, although concentrations were below the annual mean objective.
Concentrations of carbon monoxide, benzene and 1,3-butadiene are all well below their respective AQS objectives. Although there are no air quality management areas in the study area at present, detailed assessments are currently in progress, and it is likely that an AQMA will be declared in Cambridge city centre and around the ring road and associated feeder roads in Huntingdon.
The results of the local air quality assessment show that there are a small number of exceedances of the provisional 2010 annual mean PM10 AQS objective, with and without the scheme. None of the other AQS objectives are expected to be exceeded in the opening year based on raw modelling results.
There are expected to be both increases and decreases in concentrations at receptors with all scheme options. There are 4 properties with an increase in annual mean nitrogen dioxide concentrations of greater than 4µg/m3 and 27 properties with a decrease in annual mean nitrogen dioxide concentrations of greater than 4µg/m3 . The greatest increases for nitrogen dioxide with the scheme options are 8µg/m3, and the greatest decreases between 8 and 9µg/m3. For PM10 there is 1 property expected to have an increase in annual mean concentrations greater than 2µg/m3. The greatest increase with the scheme is 2µg/m3. Two properties are expected to have a decrease in annual mean PM10 concentrations of greater than 2µg/m3. The greatest decrease with the scheme is 3µg/m3.
A comparison of modelled and measured data has been undertaken for the three continuous monitoring sites near the A14. Concentrations were compared to data in 2003, and due to the high concentrations experienced in this year, to data in 2002. Modelled concentrations in 2003 were shown to under estimate the measured concentrations at all three monitoring stations, by around 30%. Modelled concentrations in 2002 were still shown to underestimate those measured at the Bar Hill and Impington sites, although they were comparable at the Godmanchester site for nitrogen dioxide. By applying adjustment factors derived from the 2002 comparison, modelled concentrations are still expected to achieve the AQS objectives, although with the 2003 adjustment factors, annual mean concentrations of nitrogen dioxide may exceed the objective at a small number of receptors.
A comparison of the modelled results with the measured data from the Atkins diffusion tube survey suggests that concentrations are being over and underestimated by as much as 55%, although in general the range is largely within ± 35%. It is recommended that a detailed dispersion study is carried out, as with an underestimate of 30% this could lead to exceedances of the 2010 annual mean nitrogen dioxide objective.
The TAG overall assessment score shows that the scheme will lead to an improvement in both PM10 and NO2 concentrations at affected properties. There is an overall increase in PM10 and NO2 concentrations at the properties near the new alignment of the A14 with all of the options. In the wider network, there is expected to be a large decrease overall in both PM10 and NO2 concentrations, which outweighs the increase near the A14.
A comparison between the Alternative Proposal and the CHUMMS Strategy indicates that the Alternative Proposal is expected to result in a greater improvement in air quality than the CHUMMS Strategy as indicted by the TAG assessment. In addition there are expected to be fewer properties with large changes in concentrations of NO2 and PM10 (change of ±4µg/m3 for NO2, ±2µg/m3 for PM10.) as compared to the Do Minimum. However, the CHUMMS Strategy is expected to result in significantly greater improvements in air quality in the areas adjacent to the Huntingdon Viaduct due to significantly lower traffic flows through this section of the route with this option.
- www.airquality.co.uk back [1]
- (Ref: Local Air Quality Management: Technical Guidance LAQM.TG(03), Defra, 2003) back [2]
