Appendix 14.2 Air Quality Modelling Study

Transcription

1 Appendix 14.2 Air Quality Modelling Study Volume 3: Environmental Statement Further Information Report Appendices Brent Cross Cricklewood: Phase 1B (North) FIR N:\Projects\WIE11453\100\8_Reports\2. ES\Volume 3 - Appendices\Volume 3 ES Further Information Report Appendices - Front Cover_2.docx

2 Appendix Air Quality Modelling Study Introduction This Appendix presents the technical information and data upon which the air quality assessment for Phase 1B (North) RMA, as presented in Chapter 14: Air Quality, is based As detailed in Chapter 14: Air Quality, the air quality assessment does not remodel the 2012 baseline or Scenario 1 (2031 End State Do Nothing scenario) as no changes have been made to the traffic flows in these scenarios and the data remains as that considered in the s.73 ES and other EIA Documentation. Scenario 2 (2031 End State Do Something scenario) has been remodelled to take account of the locations of future air quality sensitive exposure within Phase 1B (North) RMA and to include a transport sensitivity analysis associated with an increase in the amount of retail floorspace associated with the Brent Cross Shopping Centre as detailed in Phase 1B (North). The methodology for road traffic emissions presented in this chapter is consistent with that detailed for the FIR Phase 1A North RMA and approved for the s.73 ES and other EIA Documentation In order to determine the overall impacts of the Development the individual contribution from the emissions generated by the replacement bus station, bus station ventilation ducts and the energy centre have been added to the modelled traffic results for Scenario 2 (including the increase in the amount of retail floorspace). This appendix therefore builds upon Appendix 14.2 of the FIR for Phase 1A (North) RMA, and now includes the details of the assessment methodology for the replacement bus station; the bus ventilation ducts and the energy centre. For consistency the details of the traffic emissions are represented The ICP and CIA have been updated to reflect changes to the Phase 1 North construction programme, details of this are provided within Chapter 2: Description of Phase 1B North RMA and Appendix 2.1: Construction Impact Assessment (CIA) Addendum Technical Note. These changes to the programme have been considered qualitatively in Chapter 14: Air Quality in order to determine if there are any change to the potential air quality impact from those detailed in the s.73 ES and other EIA Documentation. As such no further details are presented in this appendix The results of the air quality modelling assessment, as detailed in Chapter 14: Air Quality, are presented in Appendix 14.3: Modelled Results. Air Pollutant Dispersion Model In urban areas, pollutant concentrations are primarily determined by the balance between pollutant emissions that increase concentrations, and the ability of the atmosphere to reduce and remove pollutants by dispersion, advection, reaction and deposition. An atmospheric dispersion model is used as a practical way to simulate these complex processes; which requires a range of input data, such as pollutant emissions rates and meteorological data An assessment has been undertaken using the ADMS-Roads (for the road elements and bus station) and ADMS TM (for the bus station ventilation ducts and energy centre) dispersion models. Further details on these models are discussed below. ADMS-Roads The ADMS-Roads model is a comprehensive tool for investigating air pollution due to road traffic. On review of the Site and its surroundings ADMS-Roads was considered appropriate for the assessment of the long and short-term effects of the Development on air quality. The model uses advanced algorithms for the height-dependence of wind speed, turbulence and stability to produce improved predictions of Page 1

3 air pollutant concentrations. It can predict long-term and short-term concentrations, including percentile concentrations ADMS-Roads is a formally validated model, developed in the United Kingdom (UK) by CERC (Cambridge Environmental Research Consultants). This includes comparisons with data from the UK's air quality Automatic Urban and Rural Network (AURN) and specific verification exercises using standard field, laboratory and numerical data sets. CERC is also involved in European programmes on model harmonisation, and their models were compared favourably against other EU and U.S. EPA systems. Further information in relation to this is available from the CERC website at ADMS-Roads was used to model the emissions from road traffic and also the replacement bus station; further details are provided below. This approach was agreed with the Air Quality Officer at LB Barnet (see correspondence at the end of this appendix). ADMS ADMS 5 is a Gaussian atmospheric dispersion model widely used for investigating air pollution from controlled or fugitive emissions. The model is used for a wide range of air quality assessments, from small energy centres in urban areas to large industrial facilities. It is also used to model the dispersion of odours to determine the potential for nuisance at sensitive receptors around installations. The model uses advanced algorithms for the height-dependence of wind speed, turbulence and atmospheric stability which improve calculations of air pollutant concentrations. It can predict long-term and shortterm concentrations, as well as concentration percentiles ADMS 5 was used to model the emission from the proposed bus station ventilation ducts and energy centre once Phase 1B (North) is operational and was agreed with the Air Quality Officer at LB Barnet (see correspondence at the end of this Appendix). Further details on the bus station ventilation duct and the heating plant is provided below ADMS 5 is developed in the UK by CERC and has been extensively validated against field data sets in order to assess various configurations of the model, such as flat or complex terrain, line/area/volume sources, buildings, dry deposition, fluctuations and visible plumes. Further information in relation to the model validation is available from the CERC website. Modelled Scenarios As detailed in Chapter 14: Air Quality, the transport model (BXC DDM) includes the most recent baseline traffic survey counts and represents the detailed design highways network as per the s.73 ES and other EIA Documentation. The air quality assessment does not remodel the 2012 baseline or Scenario 1 (2031 End State Do Nothing scenario) as no changes have been made to the traffic flows in these scenarios and the data remains as that considered in the s.73 ES and other EIA Documentation. Scenario 2 (2031 End State Do Something scenario) has been remodelled to take account of the locations of future air quality sensitive exposure within Phase 1B (North) RMA and to include a transport sensitivity analysis associated with an increase in the amount of retail floorspace associated with the Brent Cross Shopping Centre as detailed in Phase 1B (North) In order to show the impacts of Phase 1B (North) the individual contribution from the emissions generated by the proposed bus station, bus station ventilation ducts and energy centre have been added to the traffic model results in order to determine the overall impacts and effects of the Development. The traffic emissions have been presented separately in order to demonstrate that there are no significant changes to the results with the increase in the retail floorspace for the Brent Cross Shopping Centre from those identified in the FIR Phase 1A North RMA In order to assess the effect of the Development, with Phase 1B (North) RMA in place, on local air quality, the following scenarios, as per the s.73 ES and other EIA Documentation were assessed: Page 2

4 Scenario 1: 2031 End State Do Minimum scenario (i.e. Without Development); and Scenario 2: 2031 End State Do Something (i.e. With Development) scenario For the traffic related emissions, a baseline scenario was also modelled to establish the existing air quality conditions around the Site, and allow a comparison and verification of the model with available air pollution monitoring data. The baseline scenario is based on year 2012, using road traffic, air pollution monitoring, and meteorological data for that year (discussed further below) In accordance with LAQM.TG(09) 1 and the LBB consultee response on the scoping document, a separate model verification of the bus station has been undertaken. This has used an assessment year of 2016 to be consistent with the latest year of monitoring data available from the Waterman study at the bus station (see Appendix 14.1: Air Quality Monitoring Survey for further details on the monitoring completed and the subheading Model Verification below). The process of the model verification for the bus station has been undertaken based on the steps detailed in LAQM.TG(09) 2 to be consistent with the approach used for the model verification of the road traffic emissions in the s73 ES and EIA Documentation and to reduce any disparities in the conclusions associated with differing verification methodologies Moreover, to take into account the recent Defra analysis 3 that historical monitoring data has not been declining in line with emission forecasts, a sensitivity analysis was undertaken for the road traffic emissions on the basis of no future reductions in pollutant concentrations (i.e. considering the potential effects of the Development against the current baseline conditions, by combining the 2031 traffic data with the 2012 background concentrations and vehicle pollutant emission rates) However, the Defra analysis also acknowledges that NOx and NO2 concentrations are likely to reduce post 2015, when the Euro 6 emission standards begin to take effect. Given that the Development is to be completed in 2031, it is very likely that concentrations will be significantly lower than those presented in the sensitivity analysis, as the Euro 6 emissions standards will have fully been implemented by then. In particular, the Mayor of London is committed to reducing emissions from buses in London. Although this scenario is very conservative, as NOx emissions and NOx / NO2 background concentrations are unlikely to remain constant over such a long period of time (nearly 20 years), it can help understand the potential effect on air quality of changes in road traffic flows only. The results for this sensitivity analysis are presented in Appendix 14.3: Modelled Results and discussed in Chapter 14: Air Quality. Road Emissions Assessment Traffic flow data for the baseline 2012, and future 2031 (Do Minimum and Do Something) scenarios were provided by AECOM. Traffic data included annual average daily traffic (AADT) flows, traffic composition (percentage of HDVs Heavy-Duty Vehicles) and vehicle speeds for the surrounding road network, derived from the SATURN transport model. Modelled speeds took into account of slow moving traffic near busy junctions and roundabouts (as provided by AECOM derived from the traffic model) Traffic flows follow a diurnal variation throughout the day and week. Therefore, a diurnal profile was used in the model to replicate how the average hourly traffic flow would vary throughout the day and the week. This was based on the average traffic distribution data from the Transport Model, provided by AECOM. Figure 14.2 of the FIR for Phase 1A (North) RMA presents the diurnal variation in traffic flows that was used in the dispersion model. Modelled Area The traffic data provided was analysed to determine the extent of the road network that needed to be considered for the air quality assessment. The road network was selected based on the definition of the affected road network, as per the Highways Agency s DMRB guidance 4, using the following criteria: Road alignment will change by 5 m or more; or Page 3

5 Daily traffic flows will change by 1,000 AADT or more; or HDV flows will change by 200 AADT or more; or Daily average speed will change by 10 km/hr or more; or Peak hour speed will change by 20 km/hr or more Based on these criteria, the roads illustrated in Figure 14.3 of the FIR for Phase 1A (North) RMA have been included in the air pollutant dispersion model. These included the main roads surrounding the Site, as well as a number of minor roads. The key roads assessed included: the A406 North Circular Road; the M1 (up to the M25 Junction); the A41 (Hendon Way/Brent Cross Flyover/Watford Way); The A5 Edgware Road/Cricklewood Broadway; and The A1 Great North Way (from the M1 to the A406) Most of these roads needed to be considered due to changes over ±1,000 AADT, whilst a smaller number of roads were selected due to a change of ±200 HDVs. The M1/A5/A406 and A41/A406 junctions also needed to be considered owing to the proposed significant changes in the road layout, as part of the Development. Emission Factors The ADMS-Roads model (version 3.2.4) was used for the assessment as detailed in the FIR Phase 1A North RMA. The model includes the latest vehicle emission factors at the time of assessment as published by Defra in the Emission Factors Toolkit (EfT) (version 6.1, published in July 2014, and based on the latest COPERT database published by the European Environment Agency) The model uses several parameters (traffic flow, percentage of HDV, speed and road type) to calculate road traffic emissions for the selected pollutants. Bus Station Emissions Overview of Modelling of Bus Station The effects of the existing bus station and the replacement bus station on local air quality has been determined by modelling the dispersion of idling bus emissions in accordance with the methodology as detailed in LAQM.TG(16) and following a guidance note from CERC 5. Idling Bus Emissions Emissions at the bus station have been determined using emission factors for a typical bus (in g/s) derived from the latest EfT (version 7), combined with the typical distance a bus would travel. As the EfT requires a vehicle speed to calculate emissions, the minimum speed of 5km/hr allowed in the EfT has been assumed. Moreover, the EfT uses the latest projections of national Euro Emissions Standard bus fleet composition for the year of assessment to calculate a weighted emission rate. The years 2016 (for the model verification) and Scenario 2 ( 2031 End State Do Something ) have been considered and the emission rates for each pollutant is provided in Table A Page 4

6 Table A Bus Station - Emission Rates (g/s) Pollutant 2016 Baseline 2031 Do Minimum 2031 Do Something NOx 3.960E E E-04 PM E E E-06 PM E E E-06 Note: (1) Derived from the latest EfT (version 7) for 77 (existing) or 81 (Scenario 2) buses entering and leaving the existing and replacement bus station per hour respectively, over a distance of 133m (representative of the distance a bus would travel in the existing bus station) and 271.9m (representative of the distance a bus would travel in the replacement bus station) The above emission rates have been entered into ADMS-Roads as an area source encompassing the area of the existing and relocated bus station The actual emissions for each hour of the day have been determined by combining the forecast number of buses per hour (during weekday and weekends) and average forecast idling times, as provided by AECOM for the existing bus station and replacement bus station (see Table A14.2.2). The idling times have been added into the ADMS-Roads as a separate diurnal profile. Table A Existing and Replacement Bus Station Hourly Bus Frequencies and Idling Times Scenario Number of Buses / Hour (Monday to Saturday) Day (6:00 to 20:00) Evening (20:00 to 00:00) Night (00:00 to 6:00) Average Idling Time (secs) Monday to Friday Saturday 2016 Existing Do Minimum and Do Something Details on the 2016 bus station model verification is provided later in this appendix (see subheading Model Verification). Bus Station Ventilation Ducts Emissions The design of the replacement bus station includes mechanical ventilation with ventilation ducts. Colt impulse fans are to be mounted to the soffit of the replacement bus station to move air from the front of the bus station to the rear. The fans and mechanical extractions include a normal operation of 6 Air Changes per Hour (AC/hr). Once the air is moved to the back of the bus station, air is extracted via two risers and released at roof level The emissions from the bus station ventilation ducts have been modelled in ADMS as an area source. Details on the ventilation duct parameters have been provided by Hilson Moran as detailed in Table A Page 5

7 Table A Bus Station Ventilation Duct Parameters Unit Grid Reference Area Duct (m 2 ) Release Rate (m/s) (a) Release Height (m) Release Temperature (deg ºC) NOx Emissions (g/s) (b) PM10 Emissions (g/s) (b) PM2.5 Emissions (g/s) (b) Duct , E E E-10 Duct , E E E-10 Note: (a) the release rate calculated based on the volume of the bus station (as 44,628m 3 ), the area of the duct (3.5m 2 ) and the number of air changes per hour (as 6 air changes per hour). (b) the emissions shown in Table A have been calculated using the latest EfT (version 7) for 81 buses entering and leaving the replacement bus station per hour, over a distance of 271.9m (representative of the distance a bus would travel in the replacement bus station). Energy Centre Emissions Stack Parameters One gas-fired Low NOx Combined Heat and Power (CHP) plant and four Low NOx gas-fired boilers is to be introduced as part of Phase 1b (North) RMA, to be located within a bespoke side-wide energy centre on Plot In order to inform the design of the energy centre and to reduce the potential impact associated with emissions released from the flue on future and proposed sensitive receptors, an initial interim air quality modelling assessment was undertaken by Waterman. Details of the stack parameters considered for the interim assessment were provided by the project M&E consultants (Hilson Moran). The details and results of this study are presented in Annex A of this Appendix Based on the interim assessment a stack height of 21.7m above ground was considered appropriate for the design of the energy centre proposed within Phase 1B (North) RMA. Data for the stack parameters used within the ADMS model assessment for the gas-fired CHP and boilers were provided by the project M&E consultants (Hilson Moran). The operating hours of the CHP and boilers are assumed to be 24 hours a day which represents a worst case assessment. Table A presents the data used in the ADMS model. Table A Stack Parameters for the Energy Centre Unit No. Grid Reference Flue Diameter (m) Release Rate (m/s) Release Height (m) Release Temperature (deg ºC) NOx Emissions (g/s) per unit ENER-G E770 (Low NOx) CHP , MHS-Ultramax (Low NOx) Boiler , Note: For gas-fired plants emission factors are not provided for PM 10 because gas-fired plants do not emit any significant level of particulates The boiler stack parameters presented in Table A have been combined using the combine multiple point source input file option within ADMS 5. Page 6

8 Building Parameters Buildings can have an effect on the dispersion of pollutants from sources and can increase the maximum predicted ground level concentrations. ADMS 5 allows buildings to be included in to the model domain as a rectangle or as a circle The buildings module is based on experiments by CERC in which there was one dominant site building and several smaller surrounding buildings less important for dispersion. Given that the Energy Centre is located in an area surrounded by roads and is not immediately surrounded by any other buildings, only the energy centre building itself has been inputted into the model as a rectangle. The parameters of the energy centre building is presented in Table A Table A Building Parameters for the Energy Centre Building X Y Height (m) Length (m) Width (m) Angle (deg) Energy Centre Sensitive Receptors The approach adopted by the UK Air Quality Strategy (AQS) is to focus on areas / locations at, and close to, ground level where members of the public (in a non-workplace area) are likely to be exposed over the averaging time of the objective in question (i.e. over 1-hour, 24-hour or annual periods). Exceedences of the AQS objectives principally relate to annual mean NO2 and PM10, and 24-hour mean PM10 concentrations, so that associated potentially sensitive locations relate mainly to residential properties and other sensitive locations (such as schools) where the public may be exposed for prolonged periods. In addition, the Scheme would introduce a hotel and areas of public space where the short-term AQS objective would apply. These areas have also been considered within the air quality assessment In total, 171 sensitive receptors have been selected along the affected road network shown in Figure The receptors are representative of the façade of existing properties closest to the main roads, the bus station and the energy centre flue that would be affected by the Development. In addition, proposed residential properties as detailed in the RMAs (as Plots 53, 54 and 113), the proposed hotel and areas of public open space have been considered. Background Pollutant Concentrations As detailed in Chapter 14: Air Quality, the air quality assessment does not remodel the traffic emissions for the 2012 baseline or Scenario 1 (2031 End State Do Nothing scenario). As such the methodology, including the background concentrations, presented in this appendix is therefore consistent with that detailed in Appendix 14.2 of the FIR Phase 1A North RMA and approved for the s.73 ES and other EIA Documentation Background pollutant concentration data (i.e. concentrations due to sources not directly taken into account in the dispersion model) have been added to the modelled concentrations, which only account for contributions from the local road traffic Background pollution data can generally be extracted from suitable air quality monitoring sites, or from the UK background pollution maps, published by Defra at a 1km 2 resolution Chalgrove Primary School urban background site, part of LB Barnet Council s air quality network, has first been identified as a suitable site. However, given the extent of the modelled area, encompassing sensitive receptors several km across LB Barnet and LB Brent, it has been deemed more suitable to Page 7

9 use the background maps, rather than a single local monitoring. Moreover, background maps include PM2.5, which is not monitored by the Chalgrove School site A comparison between the air pollutant concentrations recorded in 2012 at the monitoring site, and those from the Defra maps at the same location (the 1km 2 area encompassing the monitoring site) showed similar results, although slightly higher for the background maps (32µg/m 3 NO2 and 19µg/m 3 PM10 at the monitoring site, against 33.5µg/m 3 and 23.9µg/m 3 respectively in the maps). Therefore, the background maps have been deemed appropriate, as they correlate well with local background monitoring Background map concentrations from the relevant 1km 2 have been assigned to each sensitive receptor, based on their location. The background maps include a detailed breakdown of source contribution, and allow the user to remove the contribution of specific pollution sources already included in a dispersion model. As most of the modelled area includes a number of A-roads or motorway road links, their contribution has been removed from the maps, to avoid double counting The range (minimum and maximum) of background pollutant concentrations used at any sensitive receptor is summarised in Table A Full details of the background concentrations assigned to sensitive receptors is provided in Annex B of this document. Table A Air Pollution Background Concentrations Used in the Assessment Pollutant Background Annual Mean Concentrations (µg/m 3 ) Min Max Min Max NO PM PM As discussed above and detailed below, a separate model verification has been undertaken for the existing bus stops. This include the comparison of modelled concentrations against three diffusion tubes located at the existing bus station, monitored as part of Waterman s site specific monitoring study (see Appendix 14.1: Air Quality Monitoring Survey for further details). Background NOx and NO2 concentration have been obtained for the year 2016 from the background maps for the grid square (523500, ) the bus station diffusion tubes are located in and are presented in Table A The Defra baseline map for 2011 have been used to be consistent with the traffic emissions assessment as detailed and approved for Phase 1A North (RMA). Table A Air Pollution Background Concentrations Used in the Assessment Pollutant Background Annual Mean Concentrations (µg/m 3 ) 2016 NOx 57.6 NO Meteorological Data Meteorological data provides hourly sequential data including wind direction, wind speed, temperature, precipitation and the extent of cloud cover for each hour of a given year. As a minimum ADMS-Roads requires wind speed, wind direction, and cloud cover to compute the dispersion of pollutants Meteorological data for 2012 (for the road traffic emissions) and 2016 (for the bus station emissions) were obtained from the Heathrow Airport weather station, which is 20km southwest of the Site, and Page 8

10 considered representative of local weather conditions. Figure 14.6 of the FIR for Phase 1A (North) RMA presents the wind-rose for the meteorological data Most dispersion models do not use meteorological data if they relate to calm winds conditions, as dispersion of air pollutants is more difficult to calculate in these circumstances. ADMS-Roads treats calm wind conditions by setting the minimum wind speed to 0.75 m/s. It is recommended in Technical Guidance LAQM.TG(16) that the meteorological data file be tested within a dispersion model and the relevant output log file checked, to confirm the number of missing hours and calm hours that cannot be used by the dispersion model. This is important when considering predictions of high percentiles and the number of exceedences. Technical Guidance LAQM.TG(16) recommends that meteorological data should only be used if the percentage of usable hours is greater than 85%. The meteorological data used in the assessment for 2012 includes 8,769 lines of usable hourly data out of the total 8,784 for the year, i.e. more than 99% of usable data and for 2016 includes 8,573 lines of usable hourly data out of the total 8,784 for the year, i.e. 97.6% of useable data. Both the 2012 and 2016 data is above the 85% threshold, and is therefore adequate for the dispersion modelling. Model Data Processing The modelling results were processed to calculate the averaging periods required for comparison with air quality objectives NOx emissions from combustion sources (including vehicle exhausts) comprise principally nitric oxide (NO) and nitrogen dioxide (NO2). The emitted NO reacts with oxidants in the air (mainly ozone - O3) to form more NO2. Since it is NO2 that is associated with adverse effects on human health, the air quality standards for the protection of human health is set out for NO2 and not total NOx or NO The dispersion model was run without the chemistry reaction option (used to estimate NO2 concentrations from NOx emissions), to allow verification (see below). Instead, a suitable NOx to NO2 conversion has been used to determine NO2 concentrations from NOx concentrations. There are a variety of different approaches to convert NOx to NO2; a number of which are acceptable. For this assessment, the conversion recommended by Technical Guidance LAQM.TG(16) has been used. This is based on a conversion tool developed by Defra 7, which accounts for the difference between primary emissions of NOx, background NOx and O3 concentrations, and the different proportions of primary NO2 emissions. This approach is only applicable to annual mean concentrations Research 8 undertaken in support of Technical Guidance LAQM.TG(16) has indicated that the 1-hour mean objective for NO2 is unlikely to be exceeded at a roadside location where the annual-mean NO2 concentration is less than 60µg/m 3. The 1-hour mean objective is, therefore, not considered further within this assessment where the annual mean NO2 concentration is predicted to be less than 60µg/m For PM10, the 24-hour mean air quality objective is 50µg/m 3, not to be exceeded more than 35 times a year. In order to calculate the number of exceedances of 50μg/m 3, the relationship provided in Technical Guidance LAQM.TG(16) between the number of 24-hour mean exceedances of 50μg/m 3 and the annual mean was applied, as follows: Number of Exceedances = x (annual mean 3 ) annual mean Other Model Parameters Other parameters used in the dispersion model are described here for completeness and transparency: Page 9

11 The model requires a surface roughness value. A value of 1.5 was used, which is representative of the Site (large urban area); and The model requires the Monin-Obukhov length (a measure of the stability of the atmosphere). A value of 100m (representative of large conurbations) was used for the modelling. Model Verification Model verification is the process of comparing monitored and modelled pollutant concentrations, and, if necessary, adjusting modelled results in line with monitoring results. Discrepancies between modelled and measured concentrations can arise for a number of reasons, for example: Traffic data uncertainties; Background concentration estimates; Meteorological data uncertainties; Sources not explicitly included within the model (e.g. car parks and bus stops); Overall model limitations (e.g. treatment of roughness and meteorological data, treatment of speeds); and Uncertainty in monitoring data, particularly diffusion tubes Disparities between modelling and monitoring results generally arise as result of a combination of all of these aspects. Model verification ensures these uncertainties are investigated and minimised as far as practicable. Road Emissions As discussed in Chapter 14: Air Quality and the introduction of this appendix, this air quality assessment considers the emissions generated by the replacement bus station, the bus ventilation ducts, the energy centre and the increase in retail floorspace included with Phase 1B (North) RMA. The traffic data and assessment years remains as assessed for the FIR for Phase 1A (North) RMA. As such the calculated model verification for the baseline year of 2012 of the road emissions have not been updated and remain the same as those presented in the s.73 ES and other EIA Documentation. The methodology used remains as that detailed in LAQM.TG(09). Verification of Nitrogen Dioxide (NO2) The dispersion model was used to predict annual mean NO2 concentrations at 17 roadside monitoring sites. The location of these monitoring sites is illustrated in Figure 14.7 of the FIR for Phase 1A (North) RMA. These included NO2 diffusion tube sites operated by LB Barnet and LB Brent Councils, and roadside sites from the Waterman NO2 monitoring survey. A real-time monitoring analyser operated by LB Brent Council along the A406 North Circular Road (site BT4) was also used Table A compares the unadjusted modelled results with the monitored data. These indicate that the model under predicts NO2 concentrations at all locations; and in particular does not predict exceedences at a number of monitoring sites where exceedences have been measured. Therefore, modelled results need to be adjusted to be in line with monitored data. Table A Comparison of NO2 Modelled (Unadjusted) and Monitored Concentrations (µg/m 3 ) Site Monitored NO2 Modelled NO2 Difference (Modelled - Monitored) % Difference Page 10

12 BRT % BRT % BRT % BRT % BRT % BT % PBN % PBN % PBN % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % In bold, exceedence of the NO 2 annual mean objective of 40µg/m Technical Guidance LAQM.TG(09) suggests that where there is disparity between modelled and monitored results, appropriate adjustment should be undertaken, particularly if this is by more than 25%. The guidance suggests a number of methods for approaching model verification and adjustment. A common method, which has been used in this assessment, requires adjusting the modelled road-nox contribution, based on a comparison with the equivalent monitored road-nox concentration Results of the model verification are provided in Table A Following sensitivity tests, it was found that applying a single adjustment factor to modelled results was not suitable, due to the disparity of ratios, particularly different for monitoring sites along the main busy roads compared with other sites along more minor roads. It was deemed more suitable to determine 2 separate adjustment factors, as follows: An average ratio of between monitored and modelled road-nox concentrations was used to adjust modelled results for all sites along the main A-roads; and An average ratio of was used to adjust all other model results at sites along all other roads. Table A Model Verification Adjustment of Road-NOx Concentrations Category Site ID Monitored NO2 Monitored Road NOx Modelled Road NOx Ratio Monitored / Modelled Road NOx BRT BRT Main Roads BRT BT PBN Page 11

13 PBN Waterman_DT Waterman_DT Linear Ratio for Main Roads * BRT BRT PBN Waterman_DT Other Roads Waterman_DT Waterman_DT * Based on linear regression Waterman_DT Waterman_DT Waterman_DT Linear Ratio for Other Roads * Table A shows the comparison of adjusted modelled results with monitored NO2 concentrations. The results show a better agreement between modelled and monitored concentrations. In particular, all monitored exceedence of the NO2 annual mean objective are now predicted correctly by the model. The adjustment factors in Table A were therefore used to correct modelled results at all sensitive receptors considered in this assessment. Sensitive receptors were assigned one of these two adjustment factors, depending on their location. Table A Comparison of NO2 Adjusted Modelled and Monitored Concentrations (µg/m 3 ) Category Main Roads Other Roads Site ID Adjusted Modelled Modelled Annual Mean Monitored Annual Mean % Difference Road-NOx NO2 NO2 BRT % BRT % BRT % BT % PBN % PBN % Waterman_DT % Waterman_DT % BRT % BRT % PBN % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % Waterman_DT % In bold, exceedence of the NO 2 annual mean objective of 40µg/m 3 Page 12

14 Verification of Particulate Matter (PM10 and PM2.5) There is only one monitoring site measuring PM10 and PM2.5 within the modelled area: site BT4, operated by LB Brent Council, along the A406 North Circular Road Results of the model verification for PM10 are provided in Table A For PM2.5, it was not possible to determine a similar ratio, due to inconsistencies between the measured data and background PM2.5 data. Modelled PM2.5 concentrations have therefore been adjusted using the same adjustment factor than for PM10 (3.357). Table A Model Verification Adjustment of Road-PM10 Concentrations Site PM10 Monitored Annual Mean Background PM10 Monitored Road-PM10 Modelled Road- PM10 Ratio Monitored / Modelled Road PM10 BT Bus Station Emissions Verification of Nitrogen Dioxide (NO2) The dispersion model was used to predict annual mean NO2 concentrations at the three NO2 diffusion tube located at the existing bus station as part of the Waterman NO2 monitoring survey. The process of the model verification has been undertaken based on the steps detailed in LAQM.TG(09) to be consistent with the approach used for the road traffic emissions (as discussed above) Table A compares the unadjusted modelled results with the monitored data. These indicate that the model over predicts NO2 concentrations at all of the monitoring locations. Table A Comparison of NO2 Modelled (Unadjusted) and Monitored Concentrations (µg/m 3 ) Site Monitored NO2 Modelled NO2 Difference (Modelled - Monitored) % Difference Waterman_DT Waterman_DT Waterman_DT As above, Technical Guidance LAQM.TG(09) suggests that where there is disparity between modelled and monitored results, appropriate adjustment should be undertaken, particularly if this is by more than 25%. The guidance suggests a number of methods for approaching model verification and adjustment. A common method, which has been used in this assessment, requires adjusting the modelled road-nox contribution, based on a comparison with the equivalent monitored road-nox concentration Results of the model verification are provided in Table A Table A Model Verification Adjustment of Road (Bus) -NOx Concentrations Site ID Monitored NO2 Monitored Road NOx Modelled Road NOx Ratio Monitored / Modelled Road NOx Waterman_DT Page 13

15 Waterman_DT Waterman_DT Linear Ratio * * Based on linear regression Table A shows the comparison of adjusted modelled results with monitored NO2 concentrations. The results show a better agreement between modelled and monitored concentrations. The adjustment factor in Table A were therefore used to correct the modelled bus station NOx contribution at the modelled sensitive receptors considered in this assessment prior to converting to NO2. Table A Comparison of NO2 Adjusted Modelled and Monitored Concentrations (µg/m 3 ) Site ID Adjusted Modelled Modelled Annual Mean Monitored Annual Mean % Difference Road-NOx NO2 NO2 Waterman_DT Waterman_DT Waterman_DT In bold, exceedence of the NO 2 annual mean objective of 40µg/m 3 Page 14

16 Annexes Page 15

17 Annex A Energy Centre Stack Height Assessment November 2016 Introduction This briefing note presents the Process Contributions of nitrogen oxide (NOx) from the initial / interim air quality modelling of the proposed energy centre within the Brent Cross Phase 1B North development area. The purpose of the modelling is to identify potential air quality implications to sensitive receptors within the Brent Cross Masterplan area, and to inform the developing energy centre building design and layout. The potential air quality implications have been assessed through dispersion modelling using ADMS 5. The heating plant flue characteristics and emissions data used within ADMS 5 have been based on indicative plant supplied by Hilson Moran. The proposed energy centre would be located within plot 101 within the Phase 1B North (RMA) development area. The location of the energy centre is shown in Figure 1. Based on information provided by Hilson Moran, it would be fuelled by gas and therefore only emissions of NOx, which form nitrogen dioxide (NO2) have been considered, as other pollutants are likely to be insignificant. The AQS Objectives for NO2 relevant to this assessment are summarised in Table 1. Table 1: Summary of Relevant UK AQS Objectives Pollutant Nitrogen Dioxide (NO2) Legislation Concentration 200µg/m 3 Objective / Limit Value Measured as 1 hour mean not to be exceeded more than 18 times per year Date by which Objective to be Met 31/12/ µg/m 3 Annual Mean 31/12/2005 The EU Framework Directive 2008/50/EC 1 on ambient air quality assessment and management came into force in May 2008 and was implemented by Member States, including the UK, by June The Directive aims to protect human health and the environment by avoiding, reducing or preventing harmful concentrations of air pollutants. The Air Quality Standards Regulations 2 implement Limit Values prescribed by the EU Framework Directive 2008/50/EC. The limit values are legally binding and the Secretary of State, on behalf of the UK Government, is responsible for their implementation. The current UK Air Quality Strategy (AQS) was published in July It updates any previous strategy and sets out new objectives for Local Planning Authorities (LPAs) in undertaking their LAQM duties. The 2007 UK AQS introduces a national level policy framework for exposure reduction for fine particulate matter. Objectives in the current UK AQS are in some cases more onerous than the Limit Values set out within the relevant EU Directives and the Air Quality Standards Regulations. In addition, objectives have been established for a wider range of pollutants. 1 Council Directive 2008/50/EC of 21 May 2008 on ambient air quality and cleaner air for Europe. 2 Defra, 2010, The Air Quality Standards (England) Regulations. 3 Defra, The Air Quality Strategy for England, Scotland, Wales & Northern Ireland. Page 16

18 Assessment Methodology Energy Plant Data Indicative energy plant data used within the initial / interim assessment have been supplied by Hilson Moran. Details of the plant are presented within Table 2. The plant data is likely to change as the Masterplan is developed in more detail, and thus the air quality results presented in this briefing note are indicative only, in order to aid the determination of the optimum height of the flue necessary in order to reduce significant impacts from the energy centre within the Masterplan. Parameter plans 007C and 008 show that the maximum and minimum parameters for the location of built development within the area within which plot 101 falls are 67m and 16m respectively. The stack height has therefore been modelled at these maximum and minimum heights in order to present the full range of eventualities. Table 2: Stack Parameters for the Energy Centre Plant Unit Grid Reference Flue Diameter (m) Release Rate (m/s) (b) Release Height (m) Release Temperature (deg C) Total NOx Emissions (g/s) Boiler (a) , / CHP , / (c) Note: in For gas-fired plant, emission factors are not provided for PM 10 because gas-fired plants do not emit any significant level of particulates (a) Four boilers are proposed and have been included within the model (b) In order to comply with the London Plan, the minimum release rate as detailed with the Sustainable Design and Construction Supplementary Planning Guidance 4 (of 15m/s) have been used (c) For conservatism, emissions without a catalytic convertor have been used The Release Height has assumed to be either the minimum or maximum height of the plot the energy centre is located For the purposes of this assessment the CHP and Boilers are assumed to operate continuously throughout a year Interim Air Quality Assessment Results Energy Centre Process Contribution The results of the dispersion modelling, assuming a flue height at the maximum and minimum parameters for the plot within which the energy centre is located (e.g. a flue of either 67m or 16m) are presented in Table 3 and Table 4 below. The tables show the annual mean modelled NOx process contribution emissions at the individual development plots across the masterplan area at a range of building heights, as shown on Figure 1, for the maximum and minimum modelled stack heights. For conservatism, all NOx (100%) is assumed to be converted to NO2, rather than using a conversion factor which would show lesser NO2 contributions. In addition, in order to assign a worst-case significance, the annual mean NO2 background is considered to be above 40µg/m 3. 4 Greater London Authority (2014), Sustainable Design and Construction - Supplementary Planning Guidance, Greater London Authority, London. Page 17

19 Table 3: Annual-mean (NOx) (µg/m 3 ) Process Contribution across the Masterplan with Energy Centre Flue at 16m (minimum height) Height Above Ground (m) Masterplan Development Plot Page 18

20 Height Above Ground (m) Masterplan Development Plot Key: Green Text indicates negligible impacts, Orange Text indicates moderate impacts, and Red Text indicates substantial impacts. Page 19

21 Table 4: Annual-mean (NOx) (µg/m 3 ) Process Contribution across the Masterplan with Energy Centre Flue at 67m (maximum height) Height Above Ground (m) Masterplan Development Plot Page 20

22 Height Above Ground (m) Masterplan Development Plot Key: Green Text indicates negligible impacts, Orange Text indicates moderate impacts, and Red Text indicates substantial impacts. The results in Table 3 and Table 4 show that, when the energy centre flue is located at the maximum height of the plot (67m above ground level) it has less of an impact than when it is located at the minimum height of the plot (16m). Total Annual Mean NO2 (Process Contribution, including background concentrations and traffic emissions) In order to determine the total impact of the Energy Centre on ambient air quality, the Process Contribution (as presented in Tables 3 and 4) has been added to the modelled traffic emissions and to the future predicted air quality background concentrations as presented in Chapter 14: Air Quality of the Phase 1A North Reserved Matters Revised ES Further Information Report (May 2015), which provided a full update of the air quality impacts associated with the Scheme. The Phase 1A North Reserved Matters Revised ES air quality assessment did not model predicted air quality concentrations within each plot of the masterplan. The nearest receptors modelled within the Revised ES air quality assessment are Receptors 35 and 53 (shown in Figure 1). In the Do Something modelling scenario the predicted annual mean NO2 concentrations are 31.0µg/m 3 at Receptor 35 and 27.7µg/m 3 at Receptor 53. Therefore, if, as a worst case assumption, the maximum Process Contribution of NOx (3.5µg/m 3 as shown in Table 3 at Plot 102) is added to the maximum predicted annual mean NO2 concentrations of 31.0m 3 (at Receptor 35) then the total annual mean NO2 concentration with the maximum Energy Centre process contribution (as 34.5µg/m 3 ) is below the annual mean NO2 Air Quality Strategy Objective of 40µg/m 3. Based on the above, it is considered the contribution from the energy plant is likely to be insignificant for all stack heights. Summary The interim testing of the energy centre has indicated that, to minimise the adverse impacts at the nearby sensitive receptor locations, the height of the flue should be located above the height of the surrounding development plots (65m), or if this is not possible then as high as possible within the development plot. The flue should be designed to meet the emissions standards and exit velocities set out in the Sustainable Design and Construction SPG. However, when considering the background Page 21